a bit of clarification on M20 flywheel/clutch conversion

[ForcedFirebird]

I think you need more tape measures at your work bench :P

This is good news. Really nice to know others out there are correcting information spread on the boards. Seems like one person says something, then it get repeated over and over with no real world experience. Like I said before, it cost us an entire weekend trying to get a g260 behind an m42 - a lot of that info came from m42club.

[bmwman91]

Irish, one thing you might want to try is measuring the parallelism from the TOBs' push-tabs (the 2 little wings that the pivot fork pushes on). You can probably just use some calipers to measure the distance from them to the back of the TOB body to see if they match. That's what the pivot fork pushes on and makes for a better datum plane to measure from.

Other than that, great work! I ran the spacer PLUS 323i TOB for a number of years with no problems. When I installed my Metric Mechanic M42 last month, they sent me an M20 flywheel and M20 TOB with it, and I did NOT use the M42 spacer ring. So really, it sounds like any combo will work out. When I installed the slave cylinder, it was indeed putting a pre-load on the pivot fork so it isn't like the setup is loose and flopping around. Those guys have done many flywheel swaps on all sorts of engines, and they didn't mention the need for the spacer ring. So, I think that the only reason that anyone ever started using it was because the stock M20 flywheel hots the bolts on the back of the oil pan.

[irish44j]

Irish, one thing you might want to try is measuring the parallelism from the TOBs' push-tabs (the 2 little wings that the pivot fork pushes on). You can probably just use some calipers to measure the distance from them to the back of the TOB body to see if they match. That's what the pivot fork pushes on and makes for a better datum plane to measure from.

Other than that, great work! I ran the spacer PLUS 323i TOB for a number of years with no problems. When I installed my Metric Mechanic M42 last month, they sent me an M20 flywheel and M20 TOB with it, and I did NOT use the M42 spacer ring. So really, it sounds like any combo will work out. When I installed the slave cylinder, it was indeed putting a pre-load on the pivot fork so it isn't like the setup is loose and flopping around. Those guys have done many flywheel swaps on all sorts of engines, and they didn't mention the need for the spacer ring. So, I think that the only reason that anyone ever started using it was because the stock M20 flywheel hots the bolts on the back of the oil pan.

yep, yoshi (shiboujian) mentioned that to me today, so I'll do that when I get home from work. Not sure why I didn't think of it last night. Will post another pic once I do!

[irish44j]

I think you need more tape measures at your work bench :P

This is good news. Really nice to know others out there are correcting .

just like all tools....somehow I can never find one when I need it, so I buy another. Then months downt the road I do a big "clean-up" and boom....I have 5 tape measures, 6 12mm sockets, and four vise-grip wrenches, lol....

[MazterDizazter]

Those pictures are gold, thank you! This conversion now seems much less daunting.

[irish44j]

As promised, here are shots with the level of the "ears" on the TOB, which matter more than the overall height. As you can see, the 323i TOB on the right sits "higher" by exactly 3mm. According to those who use it, it still works either with or without the spacer. I'm thinking that by using this it reduces the "throw" of the clutch pedal before it disengages the clutch (by....3mm). I plan to use this bearing since it's new (with the spacer), so I'll report later on how the feel is. This won't happen until later this winter, so don't hold your breath ;)






Overall, I'd suggest for the EASIEST method, to just go with a stock M20 flywheel/clutch, use the spacer off the M42 flywheel, use the stock M42 TOB, and the M20 starter (or M42 starter with M20 pinion gear). That should match up perfectly to the dimensions of the stock M42 setup and should be issue-free.

[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.

[vpilarrt]

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

[irish44j]

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

[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]

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....

[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]

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]

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]

^^ truth.