a bit of clarification on M20 flywheel/clutch conversion

[OSAH racing]

I tried rubber engine mounts in my m42 and QUICKLY went back to liquid-filled. The added vibration and noise was pretty extreme. Rubber mounts work fine on a inline 6, but not on a 4-cylinder without balance shafts.

I can tell this little 4 banger engine is buzzy. The Mechanic's advice is to use only the dual mass flywheels with the m42. I am trying to decide (guess at this point) if all rubber on the drive train would improve this more than all poly. I don't want to give up on the m20 flywheel and I am not changing my suspension bushings back to rubber. what bushings were you satisfied with at the trans and differential which the liquid filled engine mounts?

[Victell]

Irish44. I had the following done m42 m20 FW, lightens to 17lbs, m20 clutch kit, 240 trans. now sure on the spacer use but i can ask. Rubber engine mounts added by the mechanic poly trans and diff bushings, all suspension bushings poly, The vibration on idle up to 4 k is excessive. more than my m20 car with all poly. loud buzzing from the drive train undecereration with a load. I had the m42 swapped in m50 out. the m50 had almost no vibration and zero buzzing under deceleration. Its so excessive i can't hear the engine running while driving the LA freeways. Can you describe how much vibration with the m20 flywheel i should expect.

I tried rubber engine mounts in my m42 and QUICKLY went back to liquid-filled. The added vibration and noise was pretty extreme. Rubber mounts work fine on a inline 6, but not on a 4-cylinder without balance shafts.

[OSAH racing]

Irish44. I had the following done m42 m20 FW, lightens to 17lbs, m20 clutch kit, 240 trans. now sure on the spacer use but i can ask. Rubber engine mounts added by the mechanic poly trans and diff bushings, all suspension bushings poly, The vibration on idle up to 4 k is excessive. more than my m20 car with all poly. loud buzzing from the drive train undecereration with a load. I had the m42 swapped in m50 out. the m50 had almost no vibration and zero buzzing under deceleration. Its so excessive i can't hear the engine running while driving the LA freeways. Can you describe how much vibration with the m20 flywheel i should expect.

[roguetoaster]

Nice update, when you do the 250 swap please do compare the TOBs again, just to see if anything important has changed with revisions over time.

[irish44j]

So since I started this thread in the first place, I though I'd update it:

I ran the M20 FW, M20 starter, M20 clutch, M42 spacer, G240, and 323i TOB for 5+ years with no issues behind my M42

Now I run the identical setup behind an M50 with the G240 (which incidentally is a direct fit to the M50)

I am about to swap in a G250 and plan to use the same setup once again, but may just use a regular 325i TOB since they're half the price of the e21 stuff.

Also, I have the Condor brass pivot ball, FWIW.

All of this is on a competition stage rally car, so it definitely takes some punishment :)

[Vandy688]

I’m not to sure on the condition of the pivot pit. I do know it is there tho as i pulled the gearbox out again as i forgot to put a little grease on the top of the pin. Is there anyway to align the clutch pedal with the brake pedal as the clutch pedal sits a little higher than the Break. I should know this, but I have had the car of the road for 6 months and totally forgot 😭

i guess taking the car for a drive and using the clutch and i would also see some improvement?

[bmwman91]

Thankyou for your reply’s. I had my slave rebuilt when I was doing the conversion and it had a good amount of resistance when installing. I would say the top 40% is soft and spongy but has little to no resistance my old m42 clutch and flywheel had some free play Aswell but wasn’t as much.

ill give the car a bleed again this week and see if it resolves things or makes things better.

when you say that on most e30s you have driven do nothing in that 30%- 40% range.Where you able to push it down until it engaged with no effort?

The first 30-40% from the top feels like there is resistance, but until I get it to at least 30% down the clutch does not feel like it is disengaging. Similarly, if you have the pedal all the ay down, it feels like it won't start to grab until the pedal is 20% of the way back up. So really, 50% or more of the pedal travel is functionally useless lol. That has been my experience on most E30's anyway, including ones with fresh new clutch/PP/TOB parts.

I just had a thought. Did you make sure that the little black plastic clutch pivot pin was installed? I could see there being excessive play/dead zone if that was forgotten since the pivot arm would have to move further to do its job.

[roguetoaster]

Thankyou for your reply’s. I had my slave rebuilt when I was doing the conversion and it had a good amount of resistance when installing. I would say the top 40% is soft and spongy but has little to no resistance my old m42 clutch and flywheel had some free play Aswell but wasn’t as much.

ill give the car a bleed again this week and see if it resolves things or makes things better.

when you say that on most e30s you have driven do nothing in that 30%- 40% range.Where you able to push it down until it engaged with no effort?

On most E30s the pedal is very light for 20% of travel, and then it ramps up from there. Resistance should increase with travel if the hydraulic system is healthy.

[Vandy688]

Thankyou for your reply’s. I had my slave rebuilt when I was doing the conversion and it had a good amount of resistance when installing. I would say the top 40% is soft and spongy but has little to no resistance my old m42 clutch and flywheel had some free play Aswell but wasn’t as much.

ill give the car a bleed again this week and see if it resolves things or makes things better.

when you say that on most e30s you have driven do nothing in that 30%- 40% range.Where you able to push it down until it engaged with no effort?

[bmwman91]

Yeah, an M20 clutch/flywheel/PP/TOB is totally compatible with the M42. A stock M20 flywheel MIGHT have clearance issues, but lightweight ones usually have material removed such that it clears the oil pan. The only issue is the difference in starter ring pitch.

When you reinstalled the slave cylinder, did the plunger hit the pivot arm and provide plenty of resistance to installation? I'd also guess that you need to bleed things, or maybe they are worn, as roguetoaster suggested.

I generally feel like the top 30-40% of the clutch pedal travel does almost nothing in every E30 I have driven. It feels like the clutch is mostly engaged by around the mid-way point as far as I can tell. But, there is a healthy amount of pedal resistance at all points, so if it feels really soft/spongy at the top then there is an issue.

[roguetoaster]

I wouldn't expect the shim to be the main source of the issue, but it can clearly contribute. Sounds more like you still have air somewhere or have wear in one of the two cylinder bores. The latter does not apply if the issue wasn't present before.

Also, new or used clutch pivot pin and pressure plate?

Also, I think we debunked the need for a specific 323 TOB as the functional difference between that and the unit that is specified for a multitude of applications is unimportant.

[Vandy688]

Hey all, first time posting and I know this thread hasn’t been touched in while. I am hoping that someone can help me.

I just converted my m42 to a m20 lightweight flywheel. Roughly around 5.6kg with minimal work done to take weight out of it. It currently has 325i clutch, pressure plate and a 323i TOB. I didn’t put the shim Plate in as my old m42flywheel was a single mass and didn’t have a shim plat. I also had no clearance issues with the m20 flywheel and back of the engine.

The issue I now have is free play in the clutch pedal, the first half of the pedal feels like it is doing no work other than moving the slave rod (I can easily push it down with my hand with no effort) the last half is when the clutch pedal gets hard and it feels like a clutch pedal with effort I can push it down.

The clutch has been bled. If I was to put the shim in behind my flywheel up against the crank would it bring my flywheel out and reduce the amount of free play I have in the pedal. Any help would be apricated and if you had this issue how did you end up fixing itHey all, first time posting and I know this thread hasn’t been touched in while. I am hoping that someone can help me.

I just converted my m42 to a m20 lightweight flywheel. Roughly around 5.6kg with minimal work done to take weight out of it. It currently has 325i clutch, pressure plate and a 323i TOB. I didn’t put the shim Plate in as my old m42flywheel was a single mass and didn’t have a shim plat. I also had no clearance issues with the m20 flywheel and back of the engine.

The issue I now have is free play in the clutch pedal, the first half of the pedal feels like it is doing no work other than moving the slave rod (I can easily push it down with my hand with no effort) the last half is when the clutch pedal gets hard and it feels like a clutch pedal with effort I can push it down.

The clutch has been bled. If I was to put the shim in behind my flywheel up against the crank would it bring my flywheel out and reduce the amount of free play I have in the pedal. Any help would be apricated and if you had this issue how did you end up fixing it

this is for a e30 318is 1990

[nd4spd13]

You shouldn't need the spacer. The stock m20 FW has a protrusion on the back that interferes with the m42 and 24v rear main seal housing. The spacer was to move the FW further back to clear this.

Agreed. Fingers crossed at least.

Will be piecing this together through December and Jan along with a replacement G240, so will report back when it's all ready to go in.

[ForcedFirebird]

Helpful bump!

Spacer from M42 if needed - I think because the fw is made for m42 I won't need it, but will test fit and see.
M42 starter

You shouldn't need the spacer. The stock m20 FW has a protrusion on the back that interferes with the m42 and 24v rear main seal housing. The spacer was to move the FW further back to clear this.

[nd4spd13]

Helpful bump!

Am planning this out for my 91 318is atm.

Found this while looking for M20/lightened flywheels. Basically all the benefits of the M20 swap, but it's lighter and you can keep M42 specific parts intact.

So my plan is:
RHD M42 flywheel (7lbs)
FX racing stage 2 clutch
M42/M20 tob 21 51 7 521 471
M20b23/M20b25 flywheel bolts 11 22 7 805 885 (M12X1.5X28)
Spacer from M42 if needed - I think because the fw is made for m42 I won't need it, but will test fit and see.
M42 starter