a bit of clarification on M20 flywheel/clutch conversion

[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.

[MazterDizazter]

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

[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....

[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!

[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.

[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.

[irish44j]

this is interesting. First off these pictures are gold. Second, It seems that both set ups work fine. The difference in ring gear height really isnt too much of an issue I dont think because the starter throw will still reach out and grab the flywheel in both situations.

I however am running the spacer AND the 323 TOB, and I have no issues to report other than a slightly stiffer clutch pedal (which I like) however it could be the aftermarket burly clutch I am running.

good to hear. Since I have a brand-new 323 TOB (and two old/nasty M42 TOBs), I'd just as well use those as well. So to get the ring gear alignment perfect I may do exactly as you have done.

So now we have 3 setups that work :)

[Dj Buttchug]

this is interesting. First off these pictures are gold. Second, It seems that both set ups work fine. The difference in ring gear height really isnt too much of an issue I dont think because the starter throw will still reach out and grab the flywheel in both situations.

I however am running the spacer AND the 323 TOB, and I have no issues to report other than a slightly stiffer clutch pedal (which I like) however it could be the aftermarket burly clutch I am running.

[irish44j]

ok, looks like we were both right in different ways:


My workbench is PERFECTLY level, first of all.
I used some blocks of EXACTLY the same thickness underneath the assemblies, simulating the mouting face of the block. So this display shows the relative heights of the entire assemblies AS MOUNTED on the engine.

All bolts are tight, and the pressure plates are cinched down to spec, with clutch plates inside.

FIRST TEST:
This is the M42 stock assembly on the left.
On the right is the M20 assembly WITH the little spacer underneath. As you can see, the ring gears on each are perfectly even. Both have a standard E30 TOB on top. As you can see, they are PERFECTLY level with each other.

So, the bottom line on this setup is that the full M20 assembly here, with the spacer and stock TOB, is exactly the same overall thickness as the stock M42 stuff.

M42 vs M20 w/spacer and stock TOB:




TEST 2:
In this test, I took out the spacer ring from below the flywheel, and put the slightly longer 323i TOB on top instead of the stock one.

Results: The ring gear is a bit off. The overall height is exactly the same. So basically, this setup should work fine as well. I'm thinking that the 323 TOB method was developed before someone thought of using the little spacer to allow use of the M42 TOB. The only thing here is that the backside of the FW would have to be milled a bit to clear the engine/sump bolts. So this method involves a BIT more work.

Looking at the starter pinion gear travel, it appears that the M20 starter OR the M42 starter with the M20 cone should both work perfectly.

Thoughts?

M42 vs M20 without spacer, with 323i TOB.

[irish44j]

I'm going to go try something more illustrative. back in a bit.

[irish44j]

It is the ring gear count that the starter gear has to match. The m42 FW and m20 FW can't be compared laying on a bench. You have to check them from the crank mounting height. The m20 has more meat on the back - the part that hits the oil pan bolts - the very same reason it's not a bolt on for the 24v motors.

I am just curious as the g26 swap cost a whole weekend on my lift with 2 sold guys working on it and one a few hours each day - just to end up with an m20 clutch pack and g240, only because we weren't going to drop the trans to swap back after pulling the trans about 8x - even with my lift, that was a looooong weekend :(

yeah I realize that about the ring gear count. But with the spacer on the M20 FW mounting surface, the ring gear is in virtually the same relative place. I measured it with my engineering tools between the two FWs. The photo I posted above was a terrible illustration of anything at all, lol and didn't show what I meant it to :P

[ForcedFirebird]

It is the ring gear count that the starter gear has to match. The m42 FW and m20 FW can't be compared laying on a bench. You have to check them from the crank mounting height. The m20 has more meat on the back - the part that hits the oil pan bolts - the very same reason it's not a bolt on for the 24v motors.

I am just curious as the g26 swap cost a whole weekend on my lift with 2 sold guys working on it and one a few hours each day - just to end up with an m20 clutch pack and g240, only because we weren't going to drop the trans to swap back after pulling the trans about 8x - even with my lift, that was a looooong weekend :(

[irish44j]

The 323 TOB is a bit longer - so I perhaps people use it with the flywheel without using the spacer (and with the back lip of the flywheel shaved to clear those bolts)?

The M20 and M42 starters are exactly the same size and have the same "throw" on the gear engagement from what I can tell. The only difference I can see (other than cosmetic things) is the gear teeth. I don't see why the M20 starter wouldn't just be drop-in in place of the M42 starter, frankly.

a few pics comparing the setups:

EDIT: see a few post down for better pics.

starters (M20 left, M42 right)


TOBs (323 left, 318 right)

[ForcedFirebird]

Why is it people use the 323 TOB? We definitely didn't use one and the car had almost a year in service and brought one of my shop mates all the way through HPDE, sold the car to another shop mate and he made it to HPDE3 with the same car (both owners on daily status), all the way up until the m42/g240 was pulled in preparation for Spec e30 just about a month ago. I know we didn't use the 323 bearing because we used what was on our shelf and we certainly never had a 323 TOB for any reason.

EDIT: And we put the m20 cone on the m42 starter...

[Dj Buttchug]

excellent, thanks. So in summary:

- don't modify the flywheel at all
- use the spacer off the M42 flywheel (the one with the rivets holding it in)
- get new M20 flywheel bolts (was going to do that anyways)
- use M20 starter as-is with no modifications
- use 323i TOB
- use all the rest stock M42 stuff (slave cyl, etc)

all correct?

yes