AJ30 – Chamber of Understanding

RX8 Project – Part 22, Engine Rebuild

To preface this I am not an engine builder, this is just the approximate process I followed more to give you all some handy reference photos and some info that might be helpful to someone. Please don’t take any of this as gospel! I still don’t even know if the engine will actually work!

Anyone reading this blog may have noticed that the mechanical work on the car seemed to stop a very long time ago. While there has been a bit of a gap due to other aspects of life getting in the way there was more progress than it may have appeared. Back in 2018, some 3 years ago as I type this, I took my recently stripped engine parts (ostensibly the block and crank) along with the custom flywheel and spacer to be checked and relevant parts balanced with a view to rebuilding the engine.

With little surprise I got a call back shortly after to tell me the pistons were not serviceable and would need replacing. Following my earlier research (mentioned in a previous post) into the Noble M12 and later cars I decided that for the power point I was aiming for (300 bhp approximately) the stock cast type pistons should be up to the job with Noble moving over to forged parts with the M400 model and target power above 400 bhp. Online I’ve seen many people reporting the cast pistons hitting their limits up around 500bhp but what their life expectancy is at that point who knows. With some luck I manged to find a set of +0.5mm oversize stock replacement pistons online ( part H663CP ) so sent these up to be checked for balance with the engine. The thing Noble did upgrade was to upgrade the factory rods with forged ones so I had already sourced some suitable rods although even that was a bit of a challenge. The ones I bought were from XPOWER Engines in Essex and are still listed on Ebay as I type this as ST220 3.0 H-section EN24 steel rods and come with ARP 2000 bolts. I’d not come across this company until this point but some research showed they are quite well known so I felt pretty confident they’d be ok.

So now I’ve got these parts all shipped up to MJA Automotive in Bromsgrove who would rebore and hone the block to match the new oversize pistons as well as giving everything a proper clean, checked and completely balanced. They’re a small firm but attention to detail was great, they even sand blasted and repainted the original crank pully because it was a bit rusty.

So now I had a pile of goodies to put together :

This picture is another good indication of how small this engine block actually is for the potential power output. You can see all the goodies here and basically everything that should be replaced was so new pistons, rings, rods, clutch, upgraded engine bearings (more on this later) and then obviously the custom flywheel and cleaned crank. This means only one thing, I had to build up the engine. Now when most people rebuild their own engine for the first time they start with something like a lawnmower engine but not me…In retrospect I probably should’ve just paid MJA to build it but I like a challenge!

First things first I decided to assemble all the pistons on the rods to have a quick win. This is as simple as taking the ring clip and pin out of the piston, putting the rod in place, sliding the pin back through and putting the ring clip back in. Add a dab of lubricant inside the small bearing before you put it together. The pin should be a slip fit on this because its a fully floating arrangement and so the rod bushing may need reaming to fit correctly if this isn’t the case. It’s also with noting these rods are not handed because in this engine they all have individual locations on the crank and do not touch each other whereas some engines have paired locations leading to the rod big end bearing having a flat side and a curved/chamfered side on the outer faces. If you see this the flat faces of the rods should be oriented to touch each other in the pair.

Comparison of used stock piston and rod and new piston and forged rod

Here you can see the state of the old pistons and the massive difference in the size of the rods. The keen eyed amongst you may notice this piston has the rings installed, what I actually did was installed all the oil rings at the bottom of the pistons but left the compression rings of so they could be correctly trimmed and fitted to the engine later. The ones show I’d slotted on for my own curiosity about how it all went together and removed shortly afterwards.

Box of assembled pistons and forged rods for S-type v6

That all looks rather shiny, I’m not used to car parts being this clean!

This was around the time I tried to find a manual for how to actually rebuild this engine with all the tolerances allowed for all the various parts and after a brief search found the S-type workshop manual located on jagrepair.com . This manual is massive at some 3300 pages and covers basically every aspect of the car but obviously since I don’t have the rest of the car I concentrated on the engine section which for this engine starts on page 635. I can’t add much on the instruction in it – it really is step by step so that’s the place to go for the detail!

So back to the things I did differently and some gratuitous photos of shiny stuff. while We’re still on the subject of piston rods I actually found and ordered some Mahle motorsport “high performance” racing bearings but curiously I found out shortly afterwards that Mahle Motorsport don’t sell a kit for this engine. After a concerning period waiting to see what would turn up and if I’d just been conned what actually arrived was the following :

Checking the Mahle racing bearings catalogue I’d already found told me this was actually a bearing for a 2.3L Duratec which is a 4 cylinder engine and I’d been shipped one complete 4 cyl bearing kit ( kit number VC1013) and half a second one to make up a complete set for the V6. Checking it all out sure enough they do seem to be the correct dimensions for this engine.

Rod bearing installation detail for S-type V6

They fit well but the only bit of strangeness is racing bearings don’t have the location notch usually found on rod bearings so a lot of care must be taken to make sure they’re correctly centred in the rod when it’s assembled. Apparently this is because the notch reduces the bearing area adjacent to the notch. More info about this can be found from Mahle themselves here . Contrary to common belief the notch isn’t there to prevent the bearing from spinning and is purely to centre it on assembly. Once the rod is assembled the the hoop stress in the bearing produces so much friction it will stay in place with no issues. Spun bearings are caused when the bearing seizes onto the crank, this is usually caused by insufficient lubrication and if this happens the bearing will spin whether or not you have the notch.

So back to the block, once it’s mounted upside down on the stand go ahead and drop the block side halves of the crank bearings in place. The parts I used here are King bearings kit number MB4056SI :

Crank bearing installation photo for S-type V6

Crank bearing photo at an angle, S-type v6

Also don’t forget to add the thrust bearing on the flywheel end. It’s a bit hard to see in the photo because I haven’t got a photo without assembly lubricant but it’s there.

Apply assembly lubricant to all the bearing faces

Now drop in the crank, carefully! then go ahead and apply assembly lubricant to all the running surfaces. In the photo the middle two rod locations aren’t lubricated yet because they’re at the back and needs rotating for access.

Next take the lower block housing and install the other bearing halves into the appropriate locations. As above apply assembly lubricant on the bearing faces.

Check the bearings are holding on as the next step involves dropping this section downward onto the upper block so make sure they don’t fall out. If they wont stay put you can lift the crank back out, drop it on this section then use it to hold the bearing shells in place when you flip it over and put it on the upper block. Run a bead of RTV along the mating face of one the two block halves before you put it together. Read the instructions on the RTV – usually you need to let it partly cure before pushing the parts together. Remember the RTV goes to the inside of the bolt holes otherwise oil will weep past the bolts. This is also why the flange is wider on the inside.

Hopefully you should have something that looks like this. Note the locations of the bolts with the M6 thread on the reverse side – these are the ones the the windage tray bolts onto so they have to be in the right positions. Torque all the bolts down following the workshop manual.

Now for the top side. We need to set the piston ring gaps which will involve working out what your gap should be (there are various online calculators now which make this easy). We need to be looking at larger gaps due to running a turbo and I wanted to make sure I had some headroom to run higher boost later without issues so worked on the side of going a touch larger. I ended up with a number of 0.57mm on the top ring and 0.72mm on the second ring but I think this is probably overly cautious. Who knows, maybe one day I’ll run nitrous. The rings are measured by inserting them into the bore, making sure they’re totally parallel to the block deck using some sort of depth tool, this can be done with a vernier caliper or a variety of other methods. You then measure the gap with feeler gauges when in this position and file back the ends of the ring as necessary to get the required gap. The filed ends need to be totally flat and parallel to each other. I put a flat file in a vice and carefully filed it down. Be careful, you can’t put it back if you go too far. Also piston rings are very brittle. Don’t mix up your top and second rings of install them wrong. I suggest buying a cheap piston ring installer plier to get them on easily.

It’s quite common to lubricate the cylinder walls prior to installing the pistons but some ring manufacturers actually specify not to do this now. Check the instructions on your rings. I used a light coat of some slightly thicker engine oil I had lying about and wiped it off with a rag. The general guidance here is assembly lubricant shouldn’t be used on cylinder walls as it prevents the rings bedding in correctly.

Next up you need a piston ring compressor to tighten up the rings to fit into the cylinder bore. Make sure you get this tight enough because why you try to tap the piston into place if the ring is sticking out relative to the bore it’s possible to break the ring. Traditionally people drive the piston in with the wooden handle of a hammer to avoid damaging the piston face. I came up with a different solution tapping a section of silicone hose to avoid damage. Be careful to line the piston up with the bore. If you can rotate you engine stand such that the piston you are trying to put in is vertical then do so, this way you are less likely to scratch the bore with the rod as you lower it in.

Using a section of hose to install pistons

The pistons should have an indication mark on it which shows which side should point to the front of the engine. In this case this is the drilled mark but on other pistons it can be an arrow on the piston face or other mark, make sure you get this right!

Once the piston is fully in the bore go underneath and carefully guide the rod onto the crank then bolt the end of the rod back on (with its bearing inside) and do up the bolts. At this point they only need to be tight enough to stop it all falling apart so even finger tight is probably enough or a little over.

Now that’s quite shiny!

One question that comes up all the time is the correct socket for ARP rod bolts. after a lot of searching I’ve found according to their catalogue they do them with two common sizes of head, either a 3/8″ AF or a 7/16″ AF, both of which are of 12 point type so standard 6 point sockets will not fit. I’ve seen numerous reports online where people are saying it’s a 10mm metric. It isn’t, a 12 point 10mm will fit over the 3/8″ head but it’s a very sloppy fit you’d be only contacting the bolt on the very top of the points making the risk of stripping the head quite high. The correct socket should be a very nice slip fit.

I’m not sure exactly which kit the rod bolts are from (or even if they are from one) because they came assembled into the rods to keep them together. ARP themselves don’t seem to to a specific kit for this engine so I would assume much like the rod bearings (which I bought from the same company) they’re actually repurposed parts from the Duratec 2.3 kits or something similar. With the forged rods they could be almost be anything just selected to fit the rod so I suggest either buying them with the rods or you can buy ARP bolts by thread and length to suit whatever you have.

Once you’ve put all your pistons in and torqued all the bolts up we move on to new head gaskets. First of check where the location sleeves are – as you look at the mating faces of the block two of the holes are larger, these are intended to have steel sleeves in which locate the head relative to the block. I installed these in the block but if you do the next few steps the same as me you might find it easier to install these into the head to make the assembly easier. The head gaskets I used were genuine Ford originals parts (actually badged FoMoCo) but sold as Jaguar parts they are specific to this version of the engine because the Ford version of the engine has different water flow routes open/blocked to make the coolant flow differently. The parts I used are as follows :

RH Head Gasket 2.5 Jaguar – C2S44649
LH Head Gasket 2.5 Jaguar – XR857984
Head Bolts (Single) – XR85387

You might want to order an ARP head stud kit at this point rather than the standard head bolts. I didn’t as at the time it was an expensive add-on (around £300) for what was supposed to be a budget project but in retrospect it might have been a safer option. I don’t have the part number for the kit noted anywhere.

Bolt on the water pipe pipe on the top front of the block at this point. It’s much easier than doing it later! Don’t forget to install the O-ring on it and for belt and braces it might be best to add some RTV round it because fixing it if it leaks is a big job involving removing at least one head.

Now the next bit is something people will probably hate me for but whatever, as I’ve said before this was supposed to be a budget build with the potential for later upgrade if it ever worked. What I did was get a decompression plate cut to space out each cylinder head a little because these engines are 10.3:1 as standard and I wanted to run a not insignificant amount of boost through it. Because my plan was to have the best response I could from the engine I still wanted to keep the CR as high as I could while having a safe enough margin after a discussion with Mike at Ferriday Engineering. While I write this in 2021 his website is giving me a security warning so I don’t know what’s going on there but his email is mike@ferriday.co.uk, I can only assume (and hope) he’s still operating because he’s a very nice and knowledgeable guy. He told me that standard 1.5mm plate would give a compression ratio of 9.1:1 which should be fine. We started under the assumption the mating face would be the same as the Mondeo V6 he already had on file but that turned out to not be the case and he ended up taking my old gaskets as a template and then during a couple revisions by email I highlighted some holes that didn’t exist in the head so could safely be taken out of the decompression plate.

The decompression plate gets bonded to the face of the heads and effectively forms an extension of it, there are a few sealers used for this but the most widely regarded of them seems to be Stag Wellseal which is a form of high temperature non setting sealer resistant to fuels and oils. It is initially quite liquid but goes very sticky rather quickly and after that its quite challenging to remove. Get a suitable plastic spreader and move quickly! Despite various tales on the internet of people using the plate with two head gaskets (one each side) that’s not how these are supposed to be used generally. The idea is the face of the head is freshly refinished and so is totally smooth and flat and the decomp plate will be the same so the actual thickness of sealer will be negligible. Add to this the plate, head and block are all aluminium and so there shouldn’t be any differential thermal expansion issues. So yes it’s technically a bit of a bodge, but it’s done in the best way we can and by all accounts should hold up to my use without issue. Plus I always have the option to get custom forged pistons made later if I want to throw lots of money at it. At the end of the day this is still a cheap engine so if it does all go wrong I’ll do something else!

S-type v6 with decompression plate test fitted

Here you can see the decomp plate in position for a trial fit before being bonded onto the head. If you look carefully you’ll notice the cylinder bores in the plate aren’t round, this is because they’re not actually round in the head gasket to provide clearance for the valves.

Its probably worth highlighting here that on this engine the head bolts are under the cams so you have to assemble the head after bolting it in place. The head bolts are M10 with 6 point hex heads but with a reduced size hex. They are recessed in narrow deep bores, I used a standard 15mm deep impact socket but it was very close to not fitting so worth checking this though if yours doesn’t fit you probably found out when you took it apart!

The head bolt tightening sequence and procedure are detailed in the workshop manual but long story short I suggest getting an angle gauge for this as they’re specified as a torque + angle. These are torque to yield bolts and so you get one shot to get it right since they’re single use.

Once the head is bolted down install the cams. At this point is doesn’t matter where in their rotation they are as we will set that later but try to put all the cam retainer pack in the same positions they came out of. Make sure to coat all bearing/contact surfaces with assembly grease.

Next if you are re-using the S-Type water fitting on this engine (though I think this applies to others as well) you will want to install this now if you haven’t already, if you don’t you won’t be able to with both heads bolted on so this is your last chance!

Now just rinse and repeat for the other head…

Once you’ve done that slip the oil pump onto the crank and bolt it in place. Hopefully at this point you should have an engine that looks a bit like this:

S-type v6 front of engine (no cover) with both heads in place

If you’ve got to this point I suggest going and having a break. This assembly will be continued in my next post…

RX8 Project – Part 18, Resurfacing Cylinder Heads the Cheap Way!

As ever do this at your own risk. For most people you’re better off just getting heads machined by a specialist but if you’re reading this blog you’re probably already aware that’s not always the way I do it!

So this idea came from me wondering how I could easily clean up the cylinder heads on the V6 without additional machining. The heads were generally in good condition so I just wanted a fresh surface for the new head gaskets to seal well on rather than trying to remove any surface damage or warping. If you have this sort of damage this method is not for you.

When I came up against this problem I decided to do some research and found quite a few people online saying you could just do it with suitable abrasive paper and a sanding block. Now I get the idea but the engineer in me sees a good possibility of some part getting ground back more than another actually increasing the issues with the head that we’re trying to remove in the first place. Around this time I spoke with a few different people who have experience with engines and they all said much the same thing – machine skimming is safest and easiest but with enough care it should be possible to do a perfectly good job by hand, the problem is getting the whole thing completely flat which is very difficult by hand. Most people who had done this seemed to have done it on engines with small cylinder heads such as single cylinder machine engines which being small are easier to get flat by hand.

The problem was absolutely one of getting something suitably flat that would cover the whole head to get the whole thing even so I started looking into what might work. I was already aware of engineers surface tables which are used for checking flatness but these are large, heavy and very expensive as they’re often made of stone or tool steel. I then looked at getting some surface ground steel plate (where a thick steel place is ground to a precision flatness) but again this seemed to be expensive and awkward. After a bit of thought I had an idea…

Ok, so at first glance this seems like a daft idea but stick with me! The cheapest and most rigid precisely flat surface I could find was a piece of toughened float glass. Specifically toughened because it is created in such as way as to pre-stress the surface which makes it both stronger and stiffer but also much more brittle – this is the glass that breaks down into granules when broken rather than shards. Initially my plan was to just order a decent sized bit but that seemed rather wasteful so I thought about it and realised second hand furniture included quite sizeable bits of the glass. I began searching eBay and Facebook marketplace to see if I could find something suitable as cheaply as possible and after a week or so found this coffee table. It was nearby and listed as local collection only with some damage to the wood veneer and scratches on top surface of the glass (so the price was unlikely to go high) and 99p no reserve starting. Couple days later I was the proud owner of a £4 coffee table!

Now you may be wondering why we aren’t bothered about the surface scratches on the glass which is likely to be a problem with any similar furniture. The reason is twofold, firstly due to this being toughened glass any scratches are likely to only be very minor and secondly the glass has a whole other side which is unlikely to have any scratches anyway so we’re going to use the underside.

I took the table apart carefully removing the top and to give additional support I placed it flat on a 19mm (3/4″) thick bit of chip board carefully screwing an section of baton at each end to stop the glass sliding about while we’re working. This assembly when then placed on my carpet which is just very hard office carpet tiles on concrete so shouldn’t allow any appreciable movement so hopefully with that stack of support the glass should be perfectly flat even with a cylinder head on it! The abrasive I will be using is wet and dry paper in a range of coarseness, get a pack of each grade you plan to use, it will take a lot of it! I made sure the wet and dry would stay in place by spraying the back of it with spray mount adhesive and putting it in place. Spray mount should also peel off relatively easily when we need to change the paper. I used 3 sheets to create an area larger than the head face in both length and width.

So now we have our setup we need to prepare the cylinder head for this. When it came off the engine it was quite grimy as you might expect so this needed addressing.

So here you can see how it was when it was (almost) fresh off the engine but with the residual head gasket material scraped off. You can see the amount of grime isn’t too bad, I have already wiped some off the top half but the bottom is a bit more representative. You can also clearly see the outline marks from the head gasket that we’re looking to remove later. This step basically involved soaking the mating face in a de-greaser then wiping it all off carefully.

Head after degreasing but before refinishing

It’s not perfect but it’s a huge improvement on where we started. The combustion chambers are considerably better. There’s some residual on the face but its more staining than anything else and will be removed by the refacing. So now we’re ready to go.

First cover the wet and dry with your chosen lubricant – water should work but I found WD40 seemed to work better as it helped the head ‘glide’ more. A light oil like 3in1 would probably be even better as it’s a little thicker again and WD40 tends to dissolve the spray adhesive as you work making the wet&dry come loose. Take the head and place it on the wet and dry (I started at 120 grit) holding both sides lightly start to slide it across the surface. There are different approaches to this where you can angle the head first one way then the other to give a crosshatch pattern. In my case I generally moved it in a long oval and this seemed to give a nice even finish but as ever your mileage may vary!

Cylinder head sat on DIY refinishing setup

You will find that as you work the oil and metal shavings will spread so I suggest doing it somewhere you don’t mind the mess!

This will take some time and effort. If the wet and dry wears down replace it. when you’re happy with the initial surface being clean of all the minor marks and debris you can go up to increasingly fine levels of grit for a better finish.

On the subject of finishes when I was doing this work I found the following information which relates the abrasive rating with the achieved resulting surface roughness – if anyone knows where this is from please let me know as I can’t seem to find out.

US Grit	UK Grit	Ra µm	Ra µinch
	P120	3	125
	P180	2	85
80		1.65	70
	P240	1.5	50
	P320	0.75	30
180		0.62	25
240		0.45	18
	P500	0.4	15
320		0.25	10

Comparison of grits vs achieved surface finish

So in the context of this I’m working in UK grit. Unfortunately the only information I could find on the required surface finishes for head gaskets came from the US so is in Ra µinch (Ra being the roughness average of the surface) but luckily this table equates everything. Generally normal gaskets seem to need a surface finish of about 50-60 Ra µinch, modern multi layer steel head gaskets require 30 Ra µinch or smoother so we need to finish at a minimum of P320. I actually went up to P400 to be safe.

Comparison between not touched and work in progress cylinder head

This is the comparison of the untouched head and the one with the first couple of grits done and so not quite finished but you can see the massive improvement made here.

I know judging by eye isn’t accurate but it’s clearly doing something good!

Keep going until you do all the grits you need and when you’re done then you need to check the flatness. I did this with an engineers straight edge (as opposed to a builders straight edge which is a big ruler) which cost £25 off ebay. This is a bit of steel that has been precision ground to be completely straight in one plane so is often only a couple mm thick but 70mm wide or more. You check the flatness by putting the straight edge perpendicular to the head (so it sticks up) and trying to slide a feeler gauge under the mid point (or as close as possible) of the area you’re checking. You need to check the width, length and both diagonals but also check across all the bores. The head should have no more than 0.075 mm off flat over the longest span on an iron head, or 0.05 mm off flat on an aluminium head on a V6. In my case the smallest feeler I have is 0.04mm so that proved it was good enough but to check it further I got some thin foil, checked the thickness with a digital micrometer which came out as 0.01mm and placed the foil on one of the central bridges of the head and put the straight edge on and it rocked on the foil. I then redid the test with the foil at the ends and the same again in other directions. Each time the straight edge was clearly resting on the foil first so the head must be flat to <0.01mm across the whole head. Unfortunately I neglected to take any photos of this stage but there’s plenty of information online.

That’s about as good as it gets so our £4 coffee table looks like a success. Plus I still own a coffee table – albeit with a few new scratches!

RX8 Project – Part 17, Changing to a concentric clutch slave.

To preface this I’ve not actually run the car with this setup yet so please make your own decision if you give it a go. This was done on the gearbox from a 2006 year RX8 5 speed box so may not be applicable to others. It looks like it should work but that’s only my opinion – your mileage may vary!

So this is a bit of an odd problem which depending on the engine you’re swapping in may not be and issue but in my case I decided a V6 was a good idea and unfortunately the standard clutch slave on the RX8 gearbox is on the top offset to one side which lines up perfectly with one of the cylinder heads on my V6. Add to this if you made the better decision mentioned earlier and made the adapter thicker you may be able to avoid this as well. But since I’m largely making this up as I go along here we are!

Now I did look into whether anyone offered a concentric slave conversion for this car but it seems that was never a thing anyone did so I set to work building my own. Luckily there was one thing I knew which would help this process quite a bit – the input shaft on the gearbox is the same diameter/spline as most Ford patterns and so a Ford part should be exactly the right clearance. Add to that I’m actually using a Ford clutch if I get the depth right everything should just match up ok.

So that’s the good news, the bad news is the RX8 gearbox was never intended to be used in this way so mounting a cylinder could be an issue. Now on the RX8 there’s a flanged sleeve mounted which the original release bearing slides on the outside of. This is held on by four bolts into the back of the bellhousing and so this appeared to be essentially the only option. The tube itself can’t stay because the new concentric slave is the same ID and so clashes with it but I thought why don’t I just unbolt the tube at the flange and bolt a suitable adapter there and we’re good to go? Well it’s never that easy is it. Under that flange is a location lip which not only keeps it concentric to the gearbox input shaft but it turns out it also the height of the shoulder accurately holds the input bearing in place behind it so if I just remove that whole part the bearing will move out of position and that will very likely result in it not having enough support and rapidly removing itself from the gearbox in small pieces.

3D model of the RX8 gearbox input bearing retainer — Unfortunately I can’t find a photo of it but the part looked like this!

Ok so I can’t just remove the flanged tube and stick an adapter plate on but how about cutting the tube down to the flange to leave a flat face above the bearing retainer and just using some longer bolts to keep it all in place. After some very careful trimming I was left with this:

Next was picking a suitable concentric slave from the Ford range. After a bit of poking about and trying to find something I could make fit I found the Teckmarx TMCS00047 which is a 3rd party part number for a 2001-2007 Mk3 Mondeo/Cougar among others which as you might have read earlier was also available with this same V6 engine I am using and this model has a few advantages firstly that both in and out hydraulics are in one direction so if I make that line up with the original position of the clutch fork I should have easy access and also that they’re threaded the standard M10x1 brake fitting thread so I can direct connect hoses or hardline as I need to make it work. another major advantage is they’re used on loads of versions of the car so they’re widely available and very cheap at under £25 delivered. It also seems that the RX8 also has almost same clutch master cylinder bore as the Mondeo (18mm vs 19mm) which should mean pedal travel is still sensible.

Now with the clutch slave accurately 3D modelled I could measure the 4 bolt flange from the gearbox bearing retainer and by overlaying the two bolt patterns aligned on the centre of the input shaft I could design an adapter which I could index the relative rotational angle of the bolt patterns in the software until the fluid connections where in the right place for the hole in the bellhousing. The resulting first version was this :

Initially I transferred this to a bit of scrap plastic to make sure I hadn’t made any stupid mistakes before spending much more time cutting a proper steel adapter plate.

Plastic prototype RX8 clutch slave adapter

So with all that checked out and nothing apparently an issue I moved onto the steel one. I did make a mistake here if you can spot it…

To make the adapter I did the same as I had done with the plastic where I printed out the design at 100% scale, stuck it to the steel and then used a centre punch to mark the centre of all the drill positions. I admit this isn’t the most accurate method but it seems to work quite well!

This is the initial adapter, the four larger holes are M8 clearance holes. on the original RX8 flanged retainer they’re 9.4mm but I think I did them 8.5mm as that’s the drill I had available and tightening up the tolerance was probably a good thing. This actually turned out to be less of a problem in the end but that’s another story. The centre hole is larger than the original design to allow for the location feature I’d overlooked on the new slave (which is 42mm OD) to sit within it.

Clutch slave adapter trial fitted to the gearbox

So it fits, I called this good progress but it should come as absolute no surprise that it wasn’t quite that simple…

Clutch slave unit fitted to adapter plate

As soon as I tried to add the clutch slave all the issues become apparent as it just clashed with everything. This told me that I’d need to change the adapter to countersunk bolts so the slave didn’t foul them. I could have changed the rotation but I wanted to avoid having lengths of pipe in the bell housing if I could. Plus I’d already made this steel adapter and didn’t want to do it again!

The other thing I noticed is that the cast webs off the original pivot point actually clashed with the adapter plate preventing it from quite sitting flat so I decided to remove some of the plate to correct this minor issue.

Now the adapter sits flat and at the same time I countersunk all the adapter bolt holes and replaced the bolts.

It all fits more or less where I wanted it but when I tried to bolt up the gearbox I saw another problem. With the bearing retainer plate, a sensible thickness for an adapter plate and the height of the concentric slave itself the slave was already almost fully pressed down so that which it may have worked initially as the clutch wore the slave would prevent the clutch from fully re-engaging. Clearly not ideal so we need to get more radical. First off the back of the clutch slave had a lip similar to the one on the RX8 flanged plate which initially I was just going to leave on and sit on top of the bearing retainer plate as it was slightly thicker than the adapter plate but that just wasn’t an option any more. Below you can the way the slave is totally compressed. Also note how close the hydraulic connection point is to the original pivot point casting.

Stack height issues in the new clutch assembly

This lip was adding a couple mm of stack height we needed to remove so I proceeded to carefully file the lip off down on the slave such that it would sit full within the adapter plate and ideally totally flush to the back of the plate.

On trying to refit this in its new position I realised I’d created another problem that I glossed over earlier – that I’d need to remove some of the original gearbox casting to make the new slave sit flat in the orientation I needed as the original clutch fork pivot point clashed with the location where I wanted the hydraulic connections on the new slave. The best method I found was a drill bit larger than the feature and just drill the top of it away until it clears the new slave.

Around this time I realised really I needed to remove the original flanged bearing retainer plate as it alone added about 4mm to the stack height so I engaged in the type of butchery that makes engineers wince. I took the flanged retainer and trimmed the flange off it. Yes I specifically mean that – if you cut through the bearing retainer ring it will reduce the height such that the bearing is no longer held tightly so you need to carefully trim off just the flange plate leaving a ring the right height fill the gap between the bearing and where the retaining plate face would be. because the new slave retaining face was now flush with the adapter plate this ring will now be held in place by that. Removing this plate now meant I had to drill yet more out of the pivot casting to prevent it clashing but that’s easy.

Final fitment of the concentric slave conversion from the original fork position

Now everything is in place and the hydraulics are accessible through the original clutch fork hole.

And all back in the car…

For anyone who may want it here’s the PDF drawing for the adapter :

RX8-concentric-clutch-adapter Download

RX8 Project – Part 16, Fitting Piston Cooling Oil Jets

These are something I hadn’t really come across until I started working on this project. While I was researching the work Noble had done developing their twin turbo engines I found the installation of piston cooling oil jets noted as one of the modifications undertaken. On the basis they found it was fine to use the stock pistons but did this mod I started doing research into what exactly they were and why they were used.

The usage of these jets seems to be almost exclusively related to turbocharged engines, both diesel and petrol due to the amount of energy released in these engines. This increased release of energy caused by burning more fuel in pressurised air generates much higher temperatures inside the engine and while the block and head are actively cooled most normal engines rely on incidental oil spray to keep the piston cool. Once you start getting the piston considerably hotter you have a couple options. Either use a piston material which will cope with much higher temperatures without degrading (either due to the temperature affecting the material properties or due to thermal expansion) or somehow cool the piston. Various materials have been used for high performance pistons to help negate the material strength and thermal expansion problems with varying degrees of success but these are generally very expensive made to order parts and well beyond the range of most. This is where the jets come in.

The jet is usually some sort of nozzle drilled into an oil gallery in the block which directs a stream of oil at the underside of each piston. This both cools and lubricates the piston and rod small end/pin.
The original Noble modification is known to have some issues but this was more of a problem with the implementation. Take a look at this : http://noblecars.org/engine.html

The basic problem of the original Noble method is that with such large drillings (probably about 4mm diameter) the cooling will be very effective because the flow rate will be high but the overall engine oil pressure will likely be very low, particularly around the main bearings because that is where they are drilled into the oil supply. Clearly the one place you don’t want low oil pressure!

So me being me I decided to improve on the situation! Firstly I found that most cars that have these fitted (unsurprisingly) use considerably smaller jets, the best example I found was a NASCAR engine using a jet of 0.75mm (I have since tried to find this page again with no luck). Not wanting to risk trying to drill a hole of such a small diameter freehand at the bottom of the cylinder bore from the top I took a slightly different approach and started looking for suitable nozzle inserts that I could use that were available easily and cheap. After a lengthy search trying to find something intended for the purpose (from either a suitable production vehicle or something) I gave up and started just trying to work out what I actually needed and realised that with the rise of home 3D printing small nozzles were actually easy to get – specifically the extruder nozzles used on these printers. These nozzles are usually brass, have an M6 thread and are available in a range of hole sizes, for me the 0.8mm version looked like a good match.

I bought a pack of four nozzles off eBay for a few pounds and decided I should see what sort of spray I actually got from them – I wanted them to produce a fine jet at the normal engine oil pressure rather than a mist as this would assure the oil reached the piston rather than most of it just hitting the inside of the cylinder bore which would achieve nothing. Because I’d decided on the M6 thread it made a test jig quite simple, just a normal M6 nut welded on the end of a bit of 12mm tube. When welding anything threaded it’s a good idea (particularly on smaller threads) to put a suitable mating part in to prevent distortion if you can. In this case I used a standard M6 bolt. After welding the nut the bolt can simply be unscrewed again but if you don’t do this the heat will often distort the thread enough that it is unusable after welding. The 12mm tube just happened to be about right for the nut but also a good size to allow a normal garden hose to fit over it. Water pressure in the UK is nominally about 3 Bar which is at least in about the right area to represent an oil pressure. Also there is the question of viscosity but my logic told me that oil being more viscous than water should not form a mist as easily, so if it worked with water oil should be fine. The test showed a solid jet out to about a meter from the nozzle and beyond that a tight stream of droplets another meter or so. This should certainly be good enough for what I need!

After this test I decided to go for it, so I ordered another set of four nozzles and started trying to work out how to actually machine the block to make them fit. Due to the position the jets need to be installed the oil feeds need to be drilled from the crank bearing housing 60° either side of the centre line to match the cylinder bore angle and also at a slight angle forward or backward (depending on which cylinder it is) so they actually come out into the shoulder at the bottom of the bores rather than just continuing between the cylinders.
First off I marked up the 60° line for each bore so I had something to line the drill up with for the angle and the starting point for the drilling. Next I found a drill bit that nicely fitted into the groove in the bearing housing so as to avoid reducing the supporting area for the bearing which as it turns out is a 3.2mm. This is the area that apparently will crack on the Noble engines – they use a significantly larger drill hole here which breaks into the bearing support lands and I suspect this is part of the issue but that’s purely speculation. There is also no issue with restricting the flow to the jets here because the jets are now significantly smaller than drilling. The next important thing is this involves drilling quite a long, narrow diameter hole through aluminium and that can be quite problematic!

First off let me say this is next bit is a bad idea all round, you either have to be very confident in your abilities with a hand drill or not care if you ruin an engine block. Ideally you want to be both! If not you will want to talk to a machine shop to do this!

Before you start remember to remove the bearing shell itself and put it somewhere safe! Aluminium is a soft material and will stick to drill bits and tend to generate heat due to friction, if it gets hot enough it can actually seize onto the drill bit causing it to break. Firstly a normal length 3.2mm drill won’t be long enough for this job, it will work to an extent but the flutes will eventually be covered by the sides of the drilled hole when you get deeper and there’s nowhere for the chips of aluminium to go. My advice is to buy a long series drill bit and use it. Start the hole with a normal bit because long bits are more flexible and can be harder to get and accurate start with but once you have a dimple that will hold the bit in place swap to the long series. Use plenty of lubricant (go on, guess how I found that out!). You can use WD40 but it can get quite expensive if you have a few holes to do as it tends to vaporise off during cutting. Thicker oils tend to protect the cutting edge more but make cutting slower but in this case aluminium is soft and so drills quickly anyway plus we’re only making a small hole so it will make little difference. Personally I used 3in1 on mine with works well and helps flush the chips out but you will need to reapply the oil to the hole regularly during the process to make sure the drill is well lubricated. You could also use engine oil or even gearbox oil but these would probably slow the process a little more. Go slowly and let the tool do the work, if you push too hard there is a serious risk of flexing the drill bit which at best will give you a hole that wanders and at worst a serious risk of snapping the drill bit.
Once the 3.2mm hole comes through into the shoulder at the bottom of the bore we need to make the M6 nozzle fit, this means tapping a suitable thread into the bore end of the drilling. First clean out all the swarf (drilling debris) from the new hole. At this stage this is just to make sure we get a nice clean thread cut. Now we have the interesting bit, to tap M6 we need a 5mm pilot drill, so we have to drill out the cylinder end of the 3.2mm drilling to 5mm with enough depth for the nozzle to screw in but the only way to do this is to do it from the top of the bore with a really long drill! I went on eBay again and bought and extra long series 5mm drill for the job. This thing is 250mm long and looks absolutely ridiculous in a cordless hand drill.

It actually looks more like it should be used on masonry but these have the normal tip and are actually for metal. If the one you buy has a flat ceramic insert in the tip you’ve bought the wrong one!

I suggest you mark the depth you need to drill to accommodate the nozzle thread (with a little extra room for tapping) on the drill bit. The actual depth here isn’t critical as long as there’s enough depth for the nozzle threads at a minimum. Again plenty of lubricant and drill with slow speed and light pressure and be very careful to keep the drill loaded straight otherwise at best your hole will be at a funny angle but at worst you may snap the drill and damage the bore surface.

Next clean the swarf out again so we can get a good thread tapped. Tapping the holes is another slightly awkward problem for the same reason as drilling the pilot hole, we need to do it from the top of the bore. I suggest going on eBay (or any of a thousand other places online) again and looking for an extra long ratchet tap wrench. These are available under any number of brands but I suspect they’re largely all from the same place. They are available in a small version, which is 250mm long and will tap M3-M10 or a large version which is 300mm long but taps M5-M12. I went for the smaller one because the smaller chuck should allow tapping tighter to the cylinder wall without damaging it and this is likely to be tight for this task. Expect this to be about £10. While you’re at it buy an M6x1 plug (bottoming) tap!

Again proceed slowly with a well lubricated tap, many people will say you need to use proper cutting compound but for a small hole in a soft material this isn’t necessary, 3in1 will be fine. Try to cut forward a bit (maybe a turn at a time or so) and then back the tool off until you feel it turn smoothly. This will help prevent the tap from clogging up and either seizing up or damaging the new thread by material being forced against it. It may be necessary to back the tap out entirely to clean the removed metal from the threads because this is effectively a blind hole. Be careful not to keep going once the tap bottoms out. If you aren’t careful it’s comparatively easy to strip the threads in the aluminium with such a small tap and then it would be awkward to repair. If you’re not confident this really isn’t an ideal job for anyone new to tapping because it relies on having a degree of ‘feel’ about what you need to do and when to stop.

Rinse and repeat five more times and congratulations you now have six neatly drilled and tapped jet positions! Before doing anything else clean everything again, I used a combination of brake clean, compressed air and a scribe. You need to make sure there is no swarf left in the drillings so you don’t risk that jet becoming clogged. Once clean you need to fit the jets. The jets I selected have an external hexagon and so can be tightened up with a socket wrench but you will need sufficient extension to reach the bottom of the cylinder bore with an appropriate sized socket. Clean all the jets with brake clean to degrease them – technically this is not necessary but it helps remove any other grime that has become stuck to the jets in manufacture/transit. Next I recommend you apply a small dab of a suitable thread locker to the jet threads, specifically I went for Loctite 243 which is a medium strength thread locker which will resist oil. You can use others but if you go for anything stronger you’ll need a blowtorch to get it out and trying to do that down a cylinder bore could be interesting! Once you have the dab of Loctite on the jet you need to screw it into the newly tapped hole – I found it easiest to do this carefully from the crank side of the block by fingertip but your mileage may vary! Once you have it in enough to keep it in place tighten it in with the socket wrench. The jets will only need to be nipped up for two important reasons; firstly they are thread locked and so will not vibrate loose and second they are small and made of brass so any more force will likely strip the hex.

That’s it, one new set of shiny piston cooling oil jets! More on this project coming soon!

RX8 Project – Part 15, Engine Strip #2

So having removed the timing chain and tensioners (see part 1) next we need to start looking at removing some more major parts of the engine.

Having already removed the cam covers already you should be looking at something like this:

Thanks to the Jag Motor Project for the image – hopefully they don’t mind me borrowing it! It seems I have misplaced my own photo of this!

You need to remove the cam bearing housings because the design of this engine has the head bolts directly under the cam making it impossible to remove the head with the cams still in place. This is worth remembering and is at least part of the reason stretch bolts are used for the head – it is impossible the re-torque them after an interval of use without removing all the timing gear. As you can see in the photo these are three smaller housings and one larger one at the front each held on with two small bolts. Basically you just need to carefully remove these bearing housings in order. I suggest marking the direction and its position on each one before removal. The position could be achieved by putting each into a small tub which is numbered. However you do this you need to know which is which and which way round they go. Remove them carefully and make sure you don’t drop any bits! Once you have removed the housings you’ll see this:

Now we have clear access to the head bolts which as you can see in the photo there are eight of. These are fairly easily removed except for one thing – the bolts are set well down into the head and there is very little room in the recess to put in a socket. You will need a 15mm socket for these bolts and a small breaker bar (or an impact gun) as they will be quite tight.

These bolts are not reusable – I mean you can but it’s a terrible idea particularly in such a critical location because odds are high it will not be up to the job. This is because “stretch” bolts rely on the material of the bolt reaching the yield point of the material at which it begins to exhibit a fairly constant elastic stretch. In effect once they start to deform they behave a bit like a very stiff spring and so if tightened correctly will hold a very accurate load without loosening and so do not need to be re-tightened after a run in period. That said hang onto them for now so you know what to order to replace them!

You can see how tight the casting is around the socket! Once all the bolts are gone you can lift the head away. It might take a little persuasion with a mallet. Make sure you have a suitable clear space to put it on once you remove it.

Now you should have this level of grime:

Obviously you can just pull off the head gasket now to improve the situation quite a bit and you can have a good look at the state of the engine:

Here you can see the cylinder bore actually looks in very good condition and even still has the factory honing marks on the bores which is a good sign it’s been working well and shouldn’t have suffered wear issues.

Now do all of that again for the other head and you should have something that looks a bit like this:

Congratulations now you have an engine with no heads but since my plan was to upgrade the rods I still needed to remove more so flip the engine over and we can get to it.

In the picture you can see the oil pump is just held on by four small black bolts. I put the crank bolt back in place just so I didn’t lose it but you would have removed this a long time ago. Once the four small bolts are out the oil pump can just be slid off the crank and put aside.

Next we need to remove the con rod bolts and this is where having the crank bolt comes in because you can put it back in finger tight and once it snugs up a bit you can turn over the engine to get access to all the rod bolts. Mark up each rod with a cylinder number and arrow for the front of the engine. I put sharpie marks across the split line of the rod to make it easier to match them up later. I had to use something to knock the piston out of the bore use something non metallic otherwise you will likely damage a surface you don’t want to damage. I used a length of wooden dowel. Do these carefully unbolting and removing one at a time. When knocking the piston out don’t forget to catch it before it falls on the floor!

So all we have left is the crank. If all you wanted to do was straight swap the rods this is as far as you need to get. Well I wanted to do a few other while I was at it (more on this in another post) so I carried on to remove the crank. This is actually pretty simple at this point, you just take out the 16 main bolts holding the lower block to the upper block along the bearings. The other thing you can see in the picture are the engine mounts, the rubbers here aren’t stock s-type, they’re actually from a V8 Land Rover (Discovery among many others). The reason for this is they’re very strong, extremely cheap (£7 a pair delivered from eBay) and have a stud each side which will fit straight onto the factory cast aluminium mounting arms and also make mounting onto the car really easy when we get to that stage!

It’s worth noting in the above picture not all the bolts are the same. This is because some have small studs on the top to allow the windage plate to be mounted (blue). Note which goes where so this can be put back later! Next you also need to remove the 6 outer bolts (red) before the block will separate.

Once all the bolts are out again you might need a gentle tap with a mallet and/or a scraper to get the block apart. Don’t drop the crank bearings!

If you’ve done all of this you should have something a bit like this in front of you:

And a heap of bits you just removed:

More to come on this project in my next post!

RX8 Project – Part 14, Engine Strip #1

After deciding to turbo the engine (see earlier posts) is became apparent I would have to upgrade the piston rods to make sure the engine wasn’t in danger of these failing and ruining the engine. This meant I needed to extract these from the engine Now bear in mind that this was the first time I’d ever taken the head off and engine before let alone removed a crank so it was likely to be quite a long and delicate process! Also accept that I was making this up as I went along, things may be in a strange order but it seemed to work!

First things first mount the engine to a suitable stand:

Here it is, it’s already upside down but that doesn’t matter! First off I took off the sump. On this engine it’s a cast alloy unit with a large front bulge which makes working around the front of the engine more awkward so I got it out the way early on.

Take off the oil pick up pipe (2xM6 bolts) to get room for the windage tray. The tray is held on by 5 nuts on some special studs on this engine, these are M10 one side to hold the lower block to the upper block but i think M5 on the top just to hold the windage tray.

Now we have exposed the moving parts of the engine and get the first look at the bits we are replacing but there’s a lot more before we get them all out. An interesting thing to note here is the absence of crank bearing caps. On this engine the block is formed in two cast pieces which joint along the crank centre line so the crank bearings are held in place by the substantial cast ribs you can see in the picture and each bearing has four M10 bolts to keep it in place with additional bolts around the outside of the casting.

Next move to the front of the engine and disconnect the hose from the block to the water pump then unbolt the water pump. On the Ford version of this engine the water pump is driven directly off one of the cams but on this Jaguar one it is a separate unit driven from the back side of the accessory belt and is held on by three small M6 bolts. Next up remove the crank bolt, there are a variety of ways to do this (the easiest probably being a decent impact gun but at this point in the project I’d not yet bought it) but the method I chose was to block the rotation of the crank using a block of wood. This is done by finding a suitable block that fits between the crank and the housing such that as the crank counterweight rotates round it is stopped by the wood. Just remember that the crank bolt undoes anticlockwise so make sure you put the block on the correct side(the bottom in the above image)!

Now you can flip the engine back up the correct way because we’re moving on to the heads This is because the cam covers need removing to take off the front engine cover.

This bit is again very simple, remove the bolts holding each coil unit in place. Again this being the Jaguar version of the engine is came from the factory with coil on plug. Next remove all the bolts around the cam cover and lift the cover away. Sometimes these get refitted with instant gasket to fix a failed cover gasket cheaply and quickly and so it may require some persuasion, I usually use a putty knife or a wallpaper scraper for this job but it can be easy to damage the faces if you’re not very careful. Alternatively plastic trim removal tools can work well. Obviously repeat the process for the other cover.

Next up we need to remove the front engine cover. This involves removing the bolts all the way round the edge, you can’t miss them, there’s loads and they’re all the same! Make sure you get them all, I think there’s 17 of them but don’t quote me on that, one is under the belt tensioner by the crank! This cover again might require a little help coming away due to the gasket but should be relatively easy. If it isn’t then you’ve missed a bolt so stop prying it!

It should look something like this! Now you can see the other feature these jag engines have – variable valve timing on the intake cams. An important point here is the crank timing wheel (the notched wheel on the crank). These have two key positions but only one is correct so carefully mark which position lines up with the key on the crank when you take it off. I recommend something permanent so when you clean all the oil residue off the mark is still visible, a centre punch mark should do it.

Next you need to remove the timing chain tensioners. These are small hydraulic cylinders that use engine oil pressure to maintain tension in the timing chain. They are held on by two bolts each. Just undo the bolts and carefully remove the tensioners from the tension arms.

Once the tension cylinders have been removed the tension arms can be lifted off their dowels and removed as well and then the chains can be lifted off and you should have something that looks a bit like this:

Now all that is clear the chain runners can be removed. These also hold the VVT solenoids and so are quite a complex bit of metal but are easily removed. I also took of the water hoses at this point just to simplicity.

Now you should be at this stage:

In the next part the engine strip will continue…

RX8 Project – Part 11, Turbo’s #2 – Wastegates

So now the project is going in the turbo direction I need to be a bit wary with how I do it. The GT1549 turbo’s I chose had positives and negatives. They looked to be exactly the right size for the engine I had, they were fairly common in one form or another and importantly the price was spot on! I still don’t understand quite how but I managed to find someone on eBay with a matching pair of these turbos fully cleaned and rebuilt for £65 each delivered! So that’s the positives, now the negatives, firstly rather than the normal bracket bolted to rear of the compressor housing to hold the wastegate actuator. On these turbos it is actually cast into the housing and so it would make rotating the housing to fit the application considerably more difficult. The second problem is they have a factory fitted actuator which isn’t adjustable more than a small amount and I really didn’t want to start tweaking a completely untested engine with no idea what was going to happen with no way of keeping the boost below the 18 psi wastegate pressure!

So getting over these problems. Having looked at the rotation problem I came to the conclusion I should be able to make them both fit with no rotation changes needed. The backup plan here was to grind off the cast in mount and custom make a bracket using a bit of steel plate if it turned out I needed to later on. This takes us to the wastegate problem. I looked at a number of ways of providing a reduction in the actuator pressure including adding springs to the rod side of the actuator and even bolting the internal wastegate solid and fitting external wastegates to the manifolds I came to the conclusion the only real way of giving a wide but reliable range of adjustment while keeping the package as small as possible would be to replace the stock actuator with an aftermarket adjustable one.

Now this is where the plan goes a bit wrong about – after looking about for ages to find a sensible option at a half sensible price the best I could come up with was this : Kinugawa Actuator

I’m under no illusions here, this is a a cheapo unit! But I strongly object to spending the cost of the car on each wastegate. The problem is even though I got these for £68 each which really is very cheap they actually cost more then the pair of turbos! Considering all this it’s still a pretty good option because it is a ‘universal’ version. It comes with a range of springs for different pressures so I can start at just a few psi and swap the springs out as needed and also comes supplied with four different actuator rods.

So here we are – actuators!

So at first glance they look ideal, but don’t let that fool you! There’s a couple engineering problems to overcome.

The first problem is this; the hole in the supplied rod end isn’t large enough for the flap actuator on the turbo. The solution is simply to drill this out to fit. I didn’t note the sizes, but it was a standard drill size.

Next up was that this ‘universal’ actuator was never really intended for a turbo this small and as such the shortest actuator rod is too long to allow the wastegate flapper to close so I had to modify that as well. The rods are nominally 6mm diameter but the end the rod end has a fine pitch thread meaning modifying that would need me to buy a fine pitch die to extend the thread. Luckily the end that goes into the actuator is a standard M6x1mm metric thread so that was the easier option.

I measured how much I needed to shorten the rod to allow the flapper to just close at one end of the rod ends adjustment. The opening pressure of the actuator is set by preload so the more it is tightened greater the boost pressure. I then simply cut the thread down to the required point and then trimmed off the excess. The good news is if I made the rod too short I three more tries for each one!

And here is the difference – it’s actually about 25mm less than it started out! Reassemble the whole thing and magically it now fits where it needs to!

The other thing you will need to do potentially at this point is change the spring. Once the actuator rod is in the actuator this is actually not too bad but be a bit fiddly. First of position the actuator so the rod is sticking downward between the jaws of a vice. Tighened the vice to hold the rod in place then undo all the housing screws. Lift off the top housing and carefully remove the diaphragm underneath. Next you need to carefully release the rod to take the load off the spring. then you just unscrew the rod and take the aluminium piston and the spring underneath out the housing. Reassembly is just the reverse but the key is to put tension on the rod again and clamp it in place again before refitting the diaphragm and cap otherwise it’s very difficult to get the diaphragm correctly positioned without any wrinkles that could cause damage or leakage.

So now we have two turbos with adjustable wastegate actuators with a potential working range covering something like 3-30psi!

RX8 Project – Part 10, Turbo!

So this is about the time this whole project started getting a bit out of hand, when I decided I was going to need more power…significantly more.

I looked into what options I had –

Option 1 – I could stay naturally aspirated and probably skim the head to increase compression a bit and get more out of it but tuning in this way can be very intricate and looked to be more involved than I wanted for the amount of power I could expect.

Option 2 – Supercharger, there are a few options here. Realistically the most common supercharger these days the Eaton M45 found on the modern Mini cooper S is just too small for this so sticking with the positive displacement type we can get an M62 from a mercedes CLK230 and with the right pulley ratio it would probably be ideal for moderate improvements. For real degrees of silliness an M90 might well be needed and these are a little harder to find.

Option 3 – Turbo, this gives a huge amount of options due to the prevalence of turbo engines at the moment and would give potential for significant power gains comparatively cheaply and without needing to align belts.

After debating for a very long time the best way to go for a road car I settled on option 3 primarily for the simplicity aspect – I know very little about the intricacies of high compression engines and I know superchargers require a level of alignment very difficult to achieve with DIY manifolds! The next obvious question is how much power? Well following finding out from Noble that the rods in the engine fold up at something a bit over 300bhp I decide that from a cost and complexity point of view I’d aim for about 280bhp as a limit so I could keep the amount of parts I needed to a minimum – famous last words!

Now there’s a huge online argument about whether two smaller turbos or a single larger one gives the best throttle response and performance. This isn’t an argument I want to get into but in my case I decided twin turbo was the way to go for two reasons. Firstly because I could close mount them under the engine to keep the overall engine package as small as possible and so simplify the pipework on the exhaust side. Secondly because due to the government publicising the benefits of diesel there are now loads of small cheap turbos about for very little money..

Getting into sizing most of the information is that Noble used two T25 turbos. Taking a look at http://www.boosttown.com/forced_induction/air_amount_calculator.php

We can see that for this engine at 6000 rpm and 0.7 bar of boost we need about 27 lbs/min of total airflow. Next we need the T25 Map for a common inducer size:

Looking at the map for the normal T25 turbo we can see that with two turbos to share the load and so only needing about 13.5 lb/hr at 1.7 pressure ratio the turbo is right in its optimal zone. Not a bad choice all in all but these are old design turbos and as a twin turbo configuration the actual amount of available exhaust will be limited so the turbo may not spool until a bit high up the rev range so I started looking at other options which would give a good improvement across a wider rev range. To achieve this a smaller exhaust housing was needed and this is where the diesel engines come in. Turbos used for diesel engines tend to have smaller exhaust housings for this very reason and they’re abundant. This led me to the GT1549, this is a manufacturer specific version of the GT1548 turbo, people have reported them to be good for 180-200bhp which is right in the area we want.

In many ways a similar map to the T25 but the spindle speeds are noticeably higher. The unit as a whole is much smaller but will have less weight in the rotating components and as a result of the smaller exhaust housing the turbo should generate boost at lower RPM. I used to have a map for the exducer which confirms this but have since misplaced it. Now before anyone tells me “you can’t use a diesel turbo on a petrol” consider this – this same turbo was used on both a huge range of diesel engines but also on the Saab 9-5 V6 petrol. That said there is also a VNT version of this turbo (GT15xxV), VNT turbos don’t last long on petrol engines by all accounts.

So here we are, the turbos :

So there you have it, a short post but a complete change in the direction of the project from where it started off and we’re only just getting started!

RX8 Project – Part 8, Flywheels Part 2

Apologies for the long delay since my last post (more than a month!), life has been getting in the way of having time to do anything on blog of late. The good news is that the RX8 project has made some progress and this blog is still no-where near the current status so there’s still plenty to come!

In flywheels part one I mentioned how I ended up in a situation where I didn’t really think the cast flywheel was save to modify and how a chance encounter led me to a solution. The problem it presented is I’m primarily an electrical/electronic engineer, while I dabble fairly extensively in mechanical things designing a flywheel isn’t exactly something that comes up every day and the precision was critical so I spent a lot of time making sure I got it right!

Critical aspects as I saw them were the bolt pattern to match the crank, bolt points for a suitable clutch and and very accurate outer diameter to allow fitment of the RX8 starter ring gear.

Looking at these criteria one at a time the bolt pattern is an interesting one. At first glance all the 8 bolts appear to be evenly spaced around the crank on a PCD (Pitch Circle Diameter – this means the centre of each of the holes is placed on a circle). After checking my early flywheel model drawings against the real flywheel I noticed that all the bolts lined up except one which was just slightly wrong; ok, approximately 2mm, enough to be considered very wrong!

This suggested the pattern wasn’t exactly what I thought so I started checking exactly what the error was in different directions to figure out what was going on. After extensive measurement I managed to work out what was wrong, the bolts were indeed on a PCD they just weren’t evenly spaced. For even spacing the bolts would be at 45° intervals but one hole was shifted 4° round the PCD so it was 41° and 49° to the two nearest holes. Combined with a 76mm PCD this made the bolt pattern line up perfectly. This is actually quite useful because it means when the crank/flywheel are balanced they cannot be reassembled in the wrong alignment.

The crank also features a location register to make sure the centre of the flywheel is perfectly centred on the crank. The register is a raised lip accurately machined to a specific outer diameter so there is no lateral slop between the parts, in this case I measured this to be 44.40mm in diameter. when I trial fitted this it needed some emery on the crank to fit but this seemed due to surface rust where the engine had been stored in a damp room for a long time. Your mileage may vary!

Next up we had the clutch, I initially planned on using the RX8 clutch as I thought it would be stronger and have more options later but on further research it turned out RX8 clutches are very expensive indeed and anything other than a stock one gets very expensive very quickly and largely need to be imported so I started looking at other options. This took me back to the idea of using a Mondeo 240mm clutch, they’re cheap, readily available and the stock ones will handle a fair amount of power. Admittedly a stock kit is highly unlikely to last long with the amount of power this project could get to but there are readily available uprated covers and plates that could be used. Plus £50 on a project that may never really work isn’t too bad, £300 for a new RX8 stock clutch is more than the car cost! I also already head the factory Mondeo flywheel to take all the appropriate dimensions from which kept the process fairly simple.

The last issue was the ring gear, this is critical because the RX8 has its starter motor on the gearbox side and when because of this the options are either re-use the RX8 starter or butcher the RX8 bellhousing to allow an engine side starter to fit. For simplicity I figured I’d go with the RX8 starter since I was getting the flywheel made anyway. Starter ring gears are whats called an interference fit on the flywheel. In essence the ring gear is intentionally slightly smaller than the flywheel it is designed to fit onto and when the two parts are either pressed or heat fitted (heating up the ring so it expands and can be slipped into place) together. It is a tiny change in size when fitted and just the friction between the two parts that prevents the ring gear slipping when the engine is started hence why this is rather critical. To simplify this I modelled a nominal 290mm for the diameter of the lip this mounts on but supplied the ring gear to the machine shop and asked them to machine to an interference fit. This led to the following design:

RX8 Flywheel V6 – Machining Drawing

After a lot of double checking with these base measurements I needed to get the correct offset from the crank to make sure the clutch plate is in the correct position to be fully engaged with the gearbox splines. This led to me modelling everything to make sure it would all fit where it needed to:

Here you can see how everything stacks up. Between the bell housing and engine there is a 10mm spacer (grey) this represents the adaptor plate thickness. Clearly the bell housing has been simplified but the overall length is correct and the position of the splines (a little hard to see in the picture) and pilot bearing diameter (the reduced diameter) on the gearbox input shaft are correct.

Unfortunately having got all of this looking right and sent it over to the machinist and work starting on it I realised a couple minor mistakes, one was that I’d not offset the flywheel to match the spacing of the bell housing caused by the adaptor plate (shown above but this picture is from a later version) but related to that I hadn’t checked the offset to make sure the starter ring gear was actually in the right position to engage with the starter!

Turned out it was a little off and actually needed more offset but unfortunately the raw material for the flywheel had been delivered and machining had already begun and sadly it wasn’t big enough to allow for this extra thickness so I needed a new plan. The best I could come up with was to add a small spacer to correct this. Luckily this also allowed an opportunity to include a new pilot bearing location. This is a bearing that locates into the end of the crank to support the engine side of the gearbox input shaft and due to the gearbox adaptor plate thickness and the fact of it being a mismatched engine and gearbox the standard bearing was now too far away to support the shaft.

RX8 V6 Crank Spacer V1

This spacer corrects the problems above and still includes the correct bolt pattern, location diameters to keep everything centred. The 35mm internal diameter is the exact size of the bearing I used. This allowed a suitable bearing and a dust seal to be pressed into place and likely stay there, that said there’s a lip in the spacer to hold the bearing up and once the gearbox shaft is in place it physically can’t fall out. It’s probably worth pointing out here that this bearing only actually moves in use when the clutch is pressed, when driving along in a gear the clutch locks the crank and input shaft together and so the bearing is rotating overall but the inside and outside are rotating at the same speed so the vast majority of the time it shouldn’t experience any wear.

The final product to be coming in part 3!

RX8 Project – Part 4, The New Engine

Following part 3 where the original rotary engine proved to be a lost cause I decided to research possible engines that could be swapped in but there were a few criteria and limitations I had:

Size – The RX8 has a reasonable size engine bay overall but due to the size and position of the standard engine there are some limiting factors to consider. I’m aware others have swapped V8’s (among others) into RX8 shells but this generally involves extensive modification of the engine bay, steering rack and even front cross member due to the length of the engine.

Weight – The RX8 is famous for being very balanced largely due to the compact size and resulting low mounting position of the standard engine. No standard piston engine will quite match up but I wanted to get as close as reasonably possible.

Power – The standard RX8 was available with either 192 or 231 bhp and so I wanted to get to ideally the upper figure (even though mine actually started as the lower 192 model) or even exceed it if possible.

Cost & availibility – I wanted and engine that was cheap to buy and for which spares were cheap and readily available. This was always intended to be a budget project to swap the engine more cheaply than replacing it.

After considering a huge number of options from things people have done before (VW 1.8t engine) to completely off the wall ideas that would probably upset all the RX8 purists (1.9 turbo diesel?) I eventually came across a couple really promising candidates – the Mazda KLDE and Ford AJ series engines. These are both very compact aluminium construction V6’s which should be short enough that no modification to the front cross member should be needed. It became apparent pretty quickly that the KLDE was hard to find and attracted a comparatively high price so I ruled this out.

The AJ V6 is related to the older KLDE and is available in a few flavours. It was produced as the AJ25 and AJ30 (2.5 and 3.0 litre respectively) and were used in a a range of cars in slightly different configurations including the Ford Mondeo ST220 (along with US Contour and Taurus), Jaguar S-type and X-Type along with several others. Some (including the S-type version) have VVT.

So after an eBay search and a hard earned £165 (including delivery) later I had this prime example of an AJ25 from an S type Jag sat on my driveway. At this stage I went for the 2.5L because the 3.0L version attracts a more premium price and since I had no real idea if it I would ever get it all together I bought the cheap version. Since the block is identical for both the logic was if I made one fit and decided I just didn’t have enough power I could swap all the custom parts over to a 3.0. Clearly there’s a lot of extraneous parts on here I won’t be using and once much of this is stripped the true compact size of the engine is a bit clearer.

There are a few reasons I picked this version of this engine. One was that the Mondeo version, which is more common, has the water pump driven from and extended camshaft on the rear of the engine because in the Mondeo the engine is in a transverse orientation. To fit the engine to the RX8 the engine will need to be installed longitudinally and the rear will have to be very close to the firewall so this is a non-starter. The Jag version has the water pump front mounted so avoids this problem. The Jag version also includes direct acting mechanical bucket cam followers and VVT. Sadly the 2.5L generally only offers 200bhp in this configuration so it’s a little down on where I really wanted to be but the torque is 240 Nm compared to the 211 Nm peak of the 231 bhp RX8 and a considerably wider torque band so it should still go well.

Around this time I found out that the Noble M12 uses this same 2.5L engine running as a twin turbo at 325 bhp. The later M400 uses the 3.0L version of the engine but they again two turbos to it and get something in the order of 425 bhp out of it with minimal additional modifications. Reports from Noble suggest it is capable of even more but was limited because they were planning on upping the power later selling this as another model but due due to the change of direction and ford taking the engine out of production this never happened. More info can be found here : Noble M12 History

I also made the decision to keep the RX8 gearbox so I could retain the standard carbon prop shaft in the RX8 so next up is the challenge of making an engine made by Ford, which was salvaged from a Jag, fit the gearbox from a Mazda!