M42/4 Native Lightened Flywheel - Going Lightweight Pros/Cons
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slowmoe30

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Re: M42/4 Native Lightened Flywheel - Going Lightweight Pros/Cons
« Reply #15 on: April 25, 2020, 09:28:33 AM »
Quote from: Delta on January 20, 2016, 01:06:00 PM
I've been looking into doing a lightweight flywheel in the near future so this interests me. I was looking for something with more holding force and a much lighter weight than stock. Ive seen the UUC stage 2 kit and was leaning towards that until now.

This flywheel is made for the m20 clutch and pressure plate though? Hmm, very interested...



Edit:
heres a link http://racehead.com.au/products-page/bmw/bmw-light-flywheel-m50-m52-m42-m44/

Uses an m20 clutch, which should be really nice! So you just used some bolts from an automatic flex plate? Are they about the same as the m20 flywheel bolts or are they shorter still?


Resurrecting this thread as I am now also interested in a lightweight flywheel conversion for my M42. Wanted to confirm something -
I think the M20s use the same bolt for the manual flywheel and the auto flex plate: 12x28mm, BMW PN 11227805885.
This lines up with the statement that the M42 flywheel bolts were too long: those are 12x50mm, BMW PN 11222243051.
Therefore it seems to me that this swap needs simply the flywheel, the M20 clutch kit (PN on RHD site), and a pack of these bolts, right?

Also, update on other lightweight flywheel options out there.
- Baseline: 7.4lb RHD Flywheel ($245), Clutch Kit (~$260), Bolts (~$30 new) still seems the cheapest option.
- 9 lb JB Racing Flywheel PN 520-040-215 currently reduced from $765 to $630. Just the flywheel.
- Fidanza Flywheel PN 195321 currently reduced from $631.64 to $536.89. Just the flywheel, no mass specified.
- UUC Stage 2 Kit can be configured a number of ways, pricier, seems to be a more track-focused option.
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bmwman91

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Re: M42/4 Native Lightened Flywheel - Going Lightweight Pros/Cons
« Reply #16 on: April 30, 2020, 12:33:48 PM »
I have an RHD 7.4lb flywheel sitting in my garage right now, and I am just waiting on the rest of the parts I need to reassemble the engine and put it back into the car.

Yes, it is the case that you need all of the M20 clutch parts, including flywheel bolts. The teeth on the ring gear differ between the M42 and M20, so you need the M42 version if you have an M42 starter. It all bolts right up. I had an 11lb M20 flywheel in there before (machined down stock one) and the clutch is a LOT stiffer with the M20 PP, so be ready for that.

Also, the M42 uses a different pilot bearing than the M20, so if you get an M20 clutch kit that includes it, do not use it!
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Onz

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Re: M42/4 Native Lightened Flywheel - Going Lightweight Pros/Cons
« Reply #17 on: August 14, 2020, 01:45:34 PM »
I used a lightened M20 flywheel. Got a std one from scrap and had it taken down to around 6kg on a lathe. Then used a 323 ring bearing and brand new M20 starter from euro car parts and M20 325i clutch. My car has plenty mods and is making 200+ bhp. No slipping and cost me under £300 including fitting.
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