So now here we are six months later and I've come to my second of two one week holidays for the year. This whole time I've still been mentally working on the car, thinking through all sorts of different problems and making plans and drawings along the way. Now I've had some time off from school, I made a trip back up home and put one of these plans into practice. However, before I can get into that, we have to go through a little story time first...
It's long been playing on my mind the fact that I'd still not fully completed the V6 RWD conversion. Sure I'd made the adapter plate, engine and box mounts, intake setup, and sump etc, but the actual connection between engine and gearbox was still missing.
The flywheel and clutch situation has been through a few revisions, both in my head and in physical work. You may remember from these posts:
that I planned to use the standard V6 flywheel with an extra ring added to increase the outer diameter to take an RX8 ring gear as well as a spacer to bring it out the correct distance to take run the RX8 clutch and pressure plate. After making the spacer (which if I'm honest now I wasn't particularly happy with my workmanship and tolerances anyway) I found that the RX8 friction disk wouldn't work with the V6 flywheel or pressure plate, meaning I would have to adapt the RX8 pressure plate to the flywheel. So upon taking it to the machinist to get his opinion on making the adaptations for the larger ring gear and pressure plate, we found that pressure plate bolt holes would end up directly on the junction between flywheel and adapter ring. This was doable but it was far from ideal. Also, the labour involved would have cost similar amounts to a fully custom flywheel anyway and thus the whole plan was put on hold for a while. You may indeed have noticed this in the complete lack of a mention of the clutch and flywheel in the following posts.
And so came about my next plan. Ever since reading @yoeddynz's viva thread, I'd been pretty keen on using a lightened flywheel to help unleash the engine's propensity for revs. Luckily, this was going to let me kill two birds with one stone. I'd decided long ago that I wanted to keep everything inside the bellhousing exchangeable with standard RX8 parts. This will allow me plenty of potential clutch upgrade options in the future. With that in mind, I went looking for RX8 lightened flywheels. Almost exclusively, lightened rotary flywheels are designed to bolt up to the automatic counterweight, rather than using the integral counterweight cast into the standard flywheels. This made my life much easier.
Now I could make an adapter that picks up the six holes in the flywheel, spaces it the correct distance to use the standard RX8 clutch and pressure plate, and bolts to the end of the crank like the normal V6 flywheel. Essentially I can make a counterweight emulator.
The next step was to decide the material to make my adapter out of. I could of course just use any old steel billet lying around the shop but my fondness for my feet kind of convinced me not to go that route. So I looked at what material is usually used for steel lightweight flywheels and found that 1045 is common. I figure if it's strong enough to take the forces on a whole flywheel, then it should be well strong enough for my much smaller diameter adapter.
Next, I had to take measurements of everything and design the actual adapter itself.
And this is what I came up with. You'll have to thank the American's for building the majority of commercial aircraft in service for my use of imperial measurements. Almost all the tools used in the industry are in imperial and because of that, all the tools I had available at school are as well. Anyway, according to these dimensions, the ring gear should end up in the same position as the RX8 relative to the bell housing face and starter, and therefore the rest of the clutch system should work as normal as well.
With all this done, I could finally go home and get stuck into it. Step one, of course, was to get the raw material into a useable state by facing it up and generally roughing it out. Thank god for power feeds and tungsten carbide tools.
Next, I turned the recess that fits over the end of the crank concentric to the outer diameter of the material. With that done, I turned the piece end for end and dialed everything back up in the four jaw to turn the spigot that that flywheel runs on. This is also concentric to the outer diameter and, by extension, the recess as well. This is obviously crucial to avoid vibrations and undue wear on bearings and so forth.
You'll also notice the stepped section on the front of the spigot. This is designed to fit the inside of the standard flywheel for reasons that will become clear later on.
With those surfaces all machined, the crucial dimensions are done and I can have a nice big exhale. This means I can move on to less nail-biting procedures.
One thing I did learn from the first spacer I made way back in the day is that measuring and drilling PCDs is a right royal pain and very difficult to do accurately with the tools I have available. So this time around I decided to forgo any and all measuring of PCDs entirely and use a far more analog method. I already have the PCD that I'm trying to match. Why would I not use it to guide my drill bit? So with that in mind, I made up some bushes to guide the pilot and tapping drill and protect the aluminium flywheel. Next, I clamped the flywheel and adapter together and shifted everything to the drill press. You can see the bush already in place in this photo.
Once I had the first hole drilled to size, I tapped it to M10 x 1.25, which is the thread used by Mazda on the automatic counterweight that this flywheel is designed to bolt to. With the first hole tapped, I bolted the flywheel to the adapter, which let me get rid of the whole clamp setup and drill the subsequent holes much more simply.
I used a similar setup for drilling the crank bolts too.
I wasn't nearly as worried about damaging this flywheel since I won't be using it once it's done its jig job, so I only used a bush for the pilot drill and just threw the final drill through using the flywheel itself as the bush.
Now that all the holes were drilled I decided I ought to check my tapped threads for strength now, rather than do all the rest of the work just to find that they strip as soon as I try to put any torque on them and junk the workpiece. So I throw the first bolt in and torque it to the high limit of the 32 - 45 ftlbs recommended by Mazda for the flexplate bolts. It goes tight, tight, tight, still tight, still turning, still turning, shit. I figure its stripped and fucked. So out it comes and sure enough, the bolt thread is gone burgers. However, the female threads are still pristine. Stoked. So in goes round two. Tight, tight, tight, still tight, still turning, still turning, shit. Again. So, out she comes and another bolt failure. This time it stretched the crap out of the bolt but still left the threads perfect.
Third time was the charm though and all the threads eventually took the torque like champs. Guess that teaches me for using the first bolts I find lying around.
Finally, I put everything back into the four jaw and faced something like 15mm off the spigot to bring it back to flush with the flywheel face and finalise the outside dimensions. Here you can see me checking the runout of the flywheel when mounted and it was well well within the 0.008" tolerance specified by the Mazda service manual.
Finally I bored the recess for the spigot bearing. I decided to use the MX6 spigot bearing, mainly because I had one available, but also because it fits the RX8 input shaft perfectly, and it was much easier to machine the larger bore for than the much smaller stock roller bearing used on the RX8.
It's a very light press fit, able to be tapped home with a mallet just like the fit in the original V6 flywheel it came out of.
Finally, after two straight 14 hour days on this thing, I was ready for a dry fit.
I used the longer crank bolts that I bought for the first spacer which gave me shed loads of thread engagement, as well as a couple of M10 bolts I had lying around for the flywheel itself. I'll get some proper high tensile ones later on.
Next was the clutch and pressure plate which I eyeballed the alignment of and used some more M8 bolts I had lying around.
Finally, I muscled the gearbox around and offered it up. With the engine and box somewhat leveled the input shaft slid right in and home over the adapter plate dowels. A couple of bolts later and I stood back to admire my handiwork.
It is a beautiful thing indeed. I couldn't help myself at this point and threw a driveshaft in the back end and a ratchet on the front and low and behold we have drive!! I have to apologise for the photo quality at this point. I think there's a smudge on the inside of my lense somehow and it wasn't having a great time with the fluorescent lights at 1:30 in the morning.
I ran it through all the gears and checked the disengagement with the BFC in the bottom of the frame, and it does indeed stop spinning the driveshaft with the clutch in while still having a small amount of wiggle to the arm when out. I also checked the starter engagement with some white paint pen and it looks to be exactly where the existing wear marks are on the starter gear. I'd have loved to hook up a battery and some jumper leads to spin it over with the starter but I did end up running out of time.
With all said and done I am absolutely stoked with how everything worked out. My measurements and calculations were apparently right on the money, and my machining workmanship and tolerances are leaps and bounds ahead of the spacer I made initially.
The final setup for my adapter situation comes out to this:
Custom 12mm steel engine to gearbox adapter plate of my own design
Custom 1045 steel flywheel adapter of my own design
Aftermarket RX8/Turbo RX7 lightweight aluminium flywheel
6 speed RX8/Turbo RX7 clutch and flywheel
MX6 spigot bearing
Stock RX8 clutch arm/release bearing
If you've made it this far though what was a whole afternoon of typing then thank you very much for reading. I'd appreciate any comments or feedback on my discussion thread which you can find here:
That's it for now. Hopefully won't be another six months before the next update but we'll have to see what happens.