a bit of clarification on M20 flywheel/clutch conversion

[mr ilia]

Has anyone done this swap recently?

I want to use:

- m20 single mass FW
- m20 clutch disk
- m20 pp
- m20 tob
- m20 starter unit to replace stock m42
- m42 FW spacer

Will this work?

[harv]

This should be a sticky.

John

[ForcedFirebird]

I replace them with 13mm hex head 8mm shaft bolts to avoid using the Allan keys, grade 10.8, just be sure to follow the new torque procedure for them (38ft/lb if memory serves me correct) vs. the 8.8 Allen key bolts. I buy them by the box of 100 since we work on e30's for a living :)

[Th318is]

perfect thanks :)

[irish44j]

I don't see why you'd need different pressure plate bolts. The PP bolts on both my M42 and M20 clutches are exactly the same. I think maybe the post is just suggesting that you get NEW bolts rather than re-using the old ones.

[Th318is]

So I got some of the shorter m20 flywheel bolts but I'm reading on a separate post that I need these http://www.ecstuning.com/ES261004/PriceAlert/ pressure plate bolts as well. Are these different from the ones used in my m42 right now? Do you need these specifically like you need the flywheel bolts? Thanks

[irish44j]

^^ truth.

[bmwman91]

Yeah, I ran the 323 TOB and spacer for a good 100k miles without any problems. It probably doesn't matter either way though. I don't like grinding things on the engine, personally.

[irish44j]

I'd just use the spacer. It takes all of 30 seconds to drill out the 2 rivets holding it on.

As far as lightening the M20 flywheel, be aware that you will get lots of transmission gear lash noise. I didn't have any with a stock 19lb M20 FW, but the 11lb Metric Mechanic one has led to a lot of "Getrag rattle." You can hear it loud and clear at idle, as well as when engine-braking. It sounds like someone tossed a hand full of nuts and bolts into the tranny! I do not believe that it is indicative of any actual problems, but it is annoying to sit at a light and have the nearby cars looking and wondering what the hell is wrong with the car!

Yeah, I already have the spacer out, but I'd like to keep the exact stock "stack height" on everything, and to do that it means either stock TOB + spacer or 323 TOB + no spacer. And since I already have a new 323 TOB sitting here....

IDK, still a number of other things to do before I put the tranny/FW back on anyhow so I'll think more about it. Seems several people are running the 323 TOB and the spacer and it works fine, so if that's the case I'll just do that.

[bmwman91]

I'd just use the spacer. It takes all of 30 seconds to drill out the 2 rivets holding it on.

As far as lightening the M20 flywheel, be aware that you will get lots of transmission gear lash noise. I didn't have any with a stock 19lb M20 FW, but the 11lb Metric Mechanic one has led to a lot of "Getrag rattle." You can hear it loud and clear at idle, as well as when engine-braking. It sounds like someone tossed a hand full of nuts and bolts into the tranny! I do not believe that it is indicative of any actual problems, but it is annoying to sit at a light and have the nearby cars looking and wondering what the hell is wrong with the car!

[irish44j]

Sounds good. For me, I'm probably going to go with the "other" easiest method and not use the spacer, and just grind down that little lip on the oil pan to clear, and use the 323 TOB for perfect spacing.

Or I'll get off my butt and have the flywheel shaved to save a couple pounds if I can get it done cheap....

[Th318is]

Thanks for the replies. I'm gonna try your EASIEST method (m20 flywheel/clutch, m42 spacer, m42 TOB and m20 starter) and I'll let you know how it works in a week or two.

[irish44j]

^^ what he said. Machining the flywheel doesn't change anything with the "hub" section - it's just removing material from the outer edges.

[vpilarrt]

Lightening the flywheel has no effect on the TOB. All proper lightening is done on the backside at the outer ring area.

[Th318is]

Thank you so much for this. I was planning on doing the swap next week and I had everything except the 323i TOB which was going to have to come all the way from Germany! Now I can go ahead with it and be back on the road sooner :D
Quick question though, can I still get away with using the m42 TOB if I machine the M20 flywheel down to lighten it? Sorry if the answer is obvious.