a bit of clarification on M20 flywheel/clutch conversion

[bmwman91]

Just for reference, I am presently running a complete M20 clutch/flywheel setup. Flywheel, PP, disc, ToB are all M20 parts. No spacer ring. The thing is that it is an 11lb M20 flywheel, so it has no problem clearing the upper pan or whatever it is that the stock one interferes with. The clutch feels and works fine.

EDIT
You do need the starter pinion gear from a late model M20. Just crack your M42 starter open and swap that in, or just toss in an M20 starter.

[E21intheRockies]

Just for reference, I am presently running a complete M20 clutch/flywheel setup. Flywheel, PP, disc, ToB are all M20 parts. No spacer ring. The thing is that it is an 11lb M20 flywheel, so it has no problem clearing the upper pan or whatever it is that the stock one interferes with. The clutch feels and works fine.

Which starter are you using, M42 or M20?

[bmwman91]

Oh yeah, it is an M42 starter with an M20 pinion gear swapped in. Editing previous post...it's been so long that I forgot about that.

[E21intheRockies]

Thanks for the info, trying to keep all these different variations of the swap straight in my head........

[AndrewBird]

One other thing to clarify, you need a late model M20 starter (if you swap the whole starter). Early model is different and won't fit.

[ForcedFirebird]

One other thing to clarify, you need a late model M20 starter (if you swap the whole starter). Early model is different and won't fit.

The nose cones swap too, so the m42 starter with the m20 end works too.

[Vivek]

Okay I have a problem. I used:
M42 tob
m20 flywheel/clutch/pp/FW bolts
m20 starter in place of my m42 one
Spacer in front of the flywheel

I believe this is what post 13 said. When I went to start my car, the starter just spun, didn't seem like it touched the flywheel. I was really excited to start my car after all this work (replaced the engine and almost everything, and this was one of my upgrades). What's wrong? Do i need to swap the nose/gear from the m20 starter to my m42 one? Is there something wrong with this starter? Did I use the wrong TOB (really fucking hope I didn't)?

EDIT: just checked blunttech and the PN's are the same for m20 and m42 TOB's, so I don't think that's the issue.

[I8UR911]

It looks like you have everything correct. I would double check the part #'s for the M20 and M42 TOB on realoem...... I'm fairly certain they are different. I did this conversion last year too. I've heard there are 2 different M20 starters; early and late. Realoem doesn't show different part #'s, but I've heard people talk about swap it. Did you still out the spacer from the M42 flywheel? That's a key part. If you don't have the correct spacer, no spacer or in the wrong place (hard to do), them this is what will happen.

Hope any of this helps and you get it figured out.

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[bmwman91]

Is the solenoid that engages the starter gear firing? I had an issue where it wasn't popping the gear out and I had to open/clean the starter to un-stick it.

[Vivek]

It looks like you have everything correct. I would double check the part #'s for the M20 and M42 TOB on realoem...... I'm fairly certain they are different. I did this conversion last year too. I've heard there are 2 different M20 starters; early and late. Realoem doesn't show different part #'s, but I've heard people talk about swap it. Did you still out the spacer from the M42 flywheel? That's a key part. If you don't have the correct spacer, no spacer or in the wrong place (hard to do), them this is what will happen.

Hope any of this helps and you get it figured out.

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Okay, so the PN's on real oem are also the same (21517521471), so it shouldn't be the TOB, phew. The early model starter from my understanding is a big fat unit, I have what I believe is a late model one (according to the seller and prior knowledge) because it's thinner. I have a spacer in front of the flywheel from an m20, it's the same thickness as the m42 spacer. As bmwman91 said, I think my starter isn't going forward and rotating, it's just spinning. I guess I'll pull it off and turn the key and see what exactly it does. Does anyone have any tips on cleaning the solenoid if that's the issue?

[I8UR911]

The spacer on the M20 flywheel is not correct..... you need the 1 from the dual mass M42. That's the issue.

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[Vivek]

The spacer on the M20 flywheel is not correct..... you need the 1 from the dual mass M42. That's the issue.

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If they're not exactly the same, they're like 99% the same. I didn't measure them but visually they looked absolutely identical, and Cabriolet on here agreed and he's worked on these cars forever. It was definitely not too thick because i still had to very slightly file down my oil pan bolts to have ~1mm of clearance.

I solved my starter issue, I had the wires hooked up wrong. Stupid rookie mistake but it was my first time doing something like this. I'll put it all back together tomorrow and hopefully it starts.

[bmwman91]

As long as the spacer is within like 1mm of the M42 spacer's thickness, AND you put it between the crank & flywheel you are fine there.

Take the starter off. Disassemble it. Clean out any crap that may be built up in the pinion gear assembly and throw-out fork. Reassemble it and test it with a spare 12V battery or a battery charger. If it works, put it back on the car. Disregard females, acquire currency.

[bflan2001]

I'm just getting back into the scene and I think I might have outdated info. I've already pieced together a setup, can you guys tell me if this will work?

E21 M20 flywheel
323i TOB
M20 clutch & PP
M42 ring gear
M42 spacer
M42 starter

[bmwman91]

If the E21 M20 flywheel is identical to the M20B25 flywheel, then yeah you should be OK.