M20 flywheel conversion - starter pinion gear Q

[KenC]

I posted this on M42Club as well.

Will an M20 starter bolt onto an M42 tranny?

Are there directions anywhere for swapping the pinion gear from the M20 starter into the M42 housing?

[peerless]

I don't consider a 4lb savings as light weight. Unless you have the M20 flywheel lightened and balanced then it might be worth it. But be aware the M42 does not like a super light flywheel and it will end up with a rough idle. In addition it will make shifts very soft since their is a lot less rotating mass to 'hit' when you shift gears. Any performance gain is likely to be negatively offset by the above problems.

Combined weights as rotating assembly
-------------------------------------------
5/90 US M42 Dual Mass. 17.25kg / 38lbs
3/89 Euro M42 Single Mass. 15.5kg / 34lbs
3/90 US 325is M20 Single Mass 15.48kg / 34lbs

M20 single mass conversion advantages:

Lighter then M42 dual mass, but same weight as M42 single mass.
1/2" more clutch surface diameter for improved load capacity on high HP M42's.
Less cost for flywheel as they are plentiful used in good condition.
All parts readily available.

Disadvantages:
Must purchases additional throw out bearing as the M20 bearing is too short. (323i)
Must use modified flywheel bolts
Must use spacer in back of flywheel for proper spacing
Must modify existing starter and install M20 pinion gear

I spent quite abit of research time into this subject. You can find the complete write up here.

http://m42club.com/forums/showthread.php?t=5696

Complete M20 conversion guide here:

http://www.blackforestindustries.com/m20flywheel.htm

[KenC]

I actually already did it. A later M20 starter just bolts right up.

My M42 clutch was toast and the flywheel was in rough shape. I had access to a nice M20 flywheel so I went for it.

Idle seems unaffected.

[Funkmasta]

This is an awesome swap. I was VERY impressed with your car (Mark D chip, and M20 flywheel).

+rep

[dude8383]

This is an awesome swap. I was VERY impressed with your car (Mark D chip, and M20 flywheel).

+rep

werd. i had a 323i flywheel that was lightened to about 13lbs and idle was smooth.

imho this is one of the best upgrades for an m42, along with markd chip!