engine swap – Page 2 – Chamber of Understanding

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!

RX8 Project – Part 2

In part two we look at finally getting the engine clear. In reality due to the time I had available this process actually took something like three months. A qualified professional mechanic can remove the engine in an RX8 in as little as three HOURS! Clearly I’m not a professional mechanic!

I didn’t fully document the process as there are any number of people who have already done excellent write ups of this but hopefully I can offer a couple of pointers to anyone trying to do this. Officially the engine should be removed by dropping out the front sub-frame and not being able to do this easily on a driveway has led me to removing the engine upwards. This adds a few minor problems along the way but nothing insurmountable

One thing I found is that you really need to remove the crank pulley to clear the front crossmember. While you probably could yank it past regardless it makes the process notably easier.

With somewhat awkward visibility it can be hard to tell whats going on but it looks like this. You do not need to remove the main bolt – the pulley is just held on by the four small bolts around it (already removed in the photo).

The next major problem is removing the engine mounts. I found it virtually impossible to get at in any conventional way. You can get a ratchet on but they’re quite tight and there’s little room, and a breaker bar doesn’t have room to move. My solution to this was to undo the bolts from the top of the engine bay with a selection of extensions. These need to be 1/2″ drive as my 3/8″ drive ones were starting to flex a bit plus you will probably need a breaker bar. Due to the angle restriction a UJ is also required. While the whole assembly looks a bit bodged it works fine.

Also the oil line connectors, these are really awkward and are usually corroded solid. Hose them liberally with WD40 and let it stew overnight if they are a problem. If you plan to use them again don’t lose the small retaining wire ring, these can be hard to replace (though can probably be replaced by a snap ring from an engineering supplier).

After another brief pause for another project we started watching some car based youtube videos (Roadkill and Mighty car mods for anyone interested) and after feeling inspired to do car-ish things and pull the engine out.

My best advice on this one is – don’t try to remove an engine when it’s dark and drizzling!

Next up, rotary engine autopsy! Coming soon!

RX8 Engine Swap Project Intro

So the RX8 project involves making what is effectively a worthless vehicle useful again. For anyone not familiar with the Mazda RX8 they are a fairly high spec 4 seater car which is most widely known because it uses a Wankle rotary engine. This type of engine does not use pistons and so is incredibly smooth in operation and in the higher power (231) version of the car revs to 10,000 RPM as standard.

Sadly for all its good points the engine has a number of down sides. In terms of behavior the engine shares a number of similarities to a two stroke piston engine, one aspect is that it is designed to burn oil in normal operation to such an extent it actually has mechanical components to inject oil into the combustion chamber. This means the oil needs to be topped up frequently and it is recommended to check it every time the fuel is filled, though this isn’t as easy it probably should be and very few people do so. As a result many engines fail rapidly due to lack of lubrication once the oil gets low.

The other common failure is with the o-rings which seal the sections of the engine to each other if these fail water gets into the combustion chamber when the cooling system is under pressure (i.e. once the engine is hot). This is one common cause of the warm start/idle problems and where water gets into the oil you get lack of lubrication failure eventually as well.

The engines are expensive to get repaired assuming the fault is detected early enough and no major damage has occurred. If major damage has occurred then sections or even the whole engine may need replacement. Either way the repair is likely to cost more than the car is actually worth and this seems to happen at something around 60-80,000 miles. The combination of all of this is that these cars are abundantly available for very little money with engines in varying degrees of failure but with relatively few miles on the clock. This leads us nicely to exhibit A:

This is a 55 plate RX8 I bought from ebay for grand total of £300 taken on the day I bought it in July 2015. While technically still road legal at this stage the car wouldn’t idle when warm so was not drive-able for any real distance without serious difficulty. In order to collect it I had to impose on a friend who has a van and car trailer for moving his racing car.

My plan for the car was to remove the engine and dismantle it to see how far gone the internals were and if possible repair the engine and reinstall it. Failing that the backup plan was to try to swap in an engine from something else simply because buying a working replacement rotary engine would cost approximately £3500!

So having got the car home the next day we started taking things out:

This may look a little unconventional but in the UK the RX8 was Thatcham security rated. Part of this involved preventing the ECU from being removed because otherwise any wannabe car thief could just swap the ECU for one from a scrap yard for which they have the matching immobiliser chip, then either hotwire it or force the ignition lock like older pre-immobiliser cars. RX8’s from other countries do not have the steel retaining plates as they do not have this rating. Since the retaining bars (gold in the picture) were several mm thick and held in place with any number of rivets the only option (well the only one we could come up with at short notice) was to drill the rivets outs. I recommend centre punching (creating a divot in the centre) the rivets before drilling because they are domed and the drill will skid off. Now technically you could probably remove all the plugs on the engine and leave the ECU in place but we wanted to allow as much room as possible to take the engine out.

Unfortunately in the RX8 the engine is mounted very low and well back with a lot of ancillaries on top of it making removal a little more time consuming:

RX8 Engine Bay — There’s an engine in there somewhere!

Incredibly the back end of the engine is nearly level with the visible firewall and the front is indicated by the alternator! Yes is really is a very small engine and this particular one is the lower power RX8 – so the output of this engine is *only* 192 bhp!

And this was basically where we got to by the end of our first day removing parts. In truth this is only about three hours in as we’d had something of a heavy night and bright sunlight wasn’t helping the situation!

More to follow shortly…