Author Topic: M42 Lightened Flighwheel? (Read 13515 times)

M42boy · « **on:** April 02, 2006, 01:21:06 AM »

I'm about to drop a clutch in my 318is. I'm interested in lightening the flywheel. Can I simply shave material off the stock flywheel or is it best to swap in a lighter flywheel?? I've heard of people with the M42 using an M20 flywheel. Does this work well. How much lighter is the M20 flywheel??

Also, wanted to know if there are any negatives or downsides to using a "lighter" flywheel? I heard someone say the stock starter won't crank the engine with the M20 cluch, so there's some modification necessary. Is this true?

Is there any of the newer cars... say, '96-'97 M42 cars with a lighter flywheel, or did they all use the same one?

Any information greatly appreciated!!!

ak96ss · « **Reply #1 on:** April 02, 2006, 07:05:45 AM »

The M42 uses a dual mass flywheel - good luck finding a shop that will even machine it, let alone lightening it. There are places that sell lighter flywheels that you can use with the M42, but I have not heard of dramatic improvements using them, so the cost/benefit ratio is not that good considering the several hundred dollar cost of a new one. Unless, of course, you need a new flywheel, in which case the lighter one is probably cheaper than a stock replacement. Using the M20 one is possible, but IIRC you will need to change the gear on the starter to match, as well as using M20 parts rather than M42 parts. I investigated briefly when I redid my clutch this past winter (in my driveway - not fun), but I don't recall that it seemed worth the expense. Having said all that, YMMV.

GrippyDrifty · « **Reply #2 on:** April 02, 2006, 02:55:53 PM »

^^^^ I beg to differ. Changing to a light-weight flywheel makes for a drastic improvement in acceleration. Gunni's car has an m20 lightened flywheel on an otherwise stock car and is doing 0-60 in around 7 seconds!!<--Compared to stock, that is at least a 2 second difference. Also, one frees up a few hp's by reducing the amount of mass that the engine has to rotate.

benefits=Better acceleration(and deceleration when down shifting), a little more HP

Negative=City driving might get a little annoying at first, considering one has to rev more to launch. Revs will drop faster, as well as go up faster, so one must shift a little quicker than normal.

I'd say DO IT!! I'm going for it as soon as I can afford one. Aluminum one's go for around $500(check out BMP). I don't know how much the m20 set up goes for, but I imagine it is cheaper. One just need to source out the parts. I guess lightening the m20 flywheel is the cheapest route.

OH BTW, I have yet to find a shop that lightens dual mass flywheels, G'luck!

ak96ss · « **Reply #3 on:** April 02, 2006, 03:06:48 PM »

Quote from: GrippyDrifty

^^^^ I beg to differ. Changing to a light-weight flywheel makes for a drastic improvement in acceleration. Gunni's car has an m20 lightened flywheel on an otherwise stock car and is doing 0-60 in around 7 seconds!!<--Compared to stock, that is at least a 2 second difference. Also, one frees up a few hp's by reducing the amount of mass that the engine has to rotate.

benefits=Better acceleration(and deceleration whenn down shifting), a little more HP

Negative=City driving might get a little more annoying at first, considering one has to rev more to launch. Revs will drop faster, as well as go up faster, so one must shift a little quicker than normal.

I'd say DO IT!! I'm going it as soon as I can afford one. Aluminum one's go for around $500(check out BMP). I don't know how much the m20 set up goes for, but I imagine it is cheaper. One just need to source out the parts. I guess lightening the m20 flywheel is the cheapest route.

OH BTW, I have yet to find a shop that lightens dual mass flywheels, G'luck!

I'll not argue that point - anything you can do to remove weight from the driveline will free up a little horsepower. I'm just saying that all the anecdotal evidence I've seen doesn't point to dramatic improvements, certainly not worth the cost of the aluminum racing ones.

I had already scored a good deal on the OEM M42 parts, considered the differences I had heard reported from those who had gone with the lightened parts, and felt it wasn't worth the effort. As I said, YMMV - a 2 second drop in 0-60 times is nothing to shake a stick at, but I'd have to see that in person. Seems to me that 2 seconds off the 0-60 equates to far more than lightening the flywheel...

bmwman91 · « **Reply #4 on:** April 02, 2006, 03:11:12 PM »

I agree, the $400+ Al FW's are not worth the $. You can get a M20 stocker lightened to within 2 or 3lbs of the Al one, for a LOT less than $400. AND, you cannot use anything other than a stock pressure plate with the Al ones (unless you spend even more $$$$$), but the steel stocker will be fine with extra strong ones.

D. Clay · « **Reply #5 on:** April 02, 2006, 03:59:18 PM »

What is involved in using the m20 flywheel. A used one goes for about $50. What else do you need. My clutch has 200,000 miles on it so I am going to be ready for a new one any day now.

johna · « **Reply #6 on:** April 02, 2006, 04:47:42 PM »

The M40 flywheel swap is much simpler than the M20. All you require is an M40 flywheel, shorter M40 flywheel bolts and an M40 clutch kit. I realise you didn't get the M40 engine in the USA but you could probably import the parts from Australia or Europe very cheaply.

GrippyDrifty · « **Reply #7 on:** April 02, 2006, 08:11:05 PM »

Quote

Seems to me that 2 seconds off the 0-60 equates to far more than lightening the flywheel...

This is from Gunni's "I Gteched the car" thread:

(I Gteched the car) and got very favorurable results

average ( best )

0-60mph 7.9 (7.5 )
0-400m 16 ( 15.75) @ 88mph (90mph)
damp conditions
based on beeing 2700lbs then it�s 107rwhp

0-60mph = 7,5 (6,9)
0-400m = 15.8 (15.4)
good conditions and perfect launch
does anybody have any gtech info to share??
Reply With Quote

m20 ltw flywheel<<<<<<<<<-----------------------

bmwman91 · « **Reply #8 on:** April 03, 2006, 01:30:28 AM »

The M20 swap requires:
M20 flywheel
M20 clutch disc & PP
E21 323i TOB...there were ~90 left in the entire US according to a BMW dealer looking through the parts inventory...2 years ago.
M20 flywheel bolts
M20 starter pinion gear
Spacer ring from M42 stock FW

asubimmer · « **Reply #9 on:** April 03, 2006, 11:15:55 AM »

I just picked up my m20 flywheel, clutch and PP sat. All the parts are used so I don't know if I am going to use the clutch or PP again. THe PP doesn't look too bad but yeah. The clutch looks ok at best. I plan on getting a stage clutch for the turbo anyway. Maybe a 6 pluck unsprung. I got it all for a great deal so I just got everything.

bmwman91 · « **Reply #10 on:** April 03, 2006, 01:25:58 PM »

Oh, and don't forget to remove the spacer ring that is riveted onto the M42 flywheel. You will need it to keep the M20 flywheel from hitting the oil pan.

Good luck finding the E21 323i TOB. I think there may be a couple places around /online that can find them, but it is getting more & more expensive to do so. Someone should try to find another working TOB for this.

M42boy · « **Reply #11 on:** April 03, 2006, 11:52:51 PM »

What is the PN# for the flywheel bolts I will need? I can't seem to find the flywheel in the parts fishe.

http://www.realoem.com/bmw/showparts.do?model=1113&mospid=47309&btnr=21_0020&hg=21&fg=05

I'd also like to confirm the M20 flywheel part number, since mine will be coming from a yard. Want to double check that it's the right part before machining and reassembly.

asubimmer · « **Reply #12 on:** April 04, 2006, 12:02:29 AM »

my bolts came w/ it

sorry I don't know the #ers

bmwman91 · « **Reply #13 on:** April 04, 2006, 09:08:14 PM »

The flywheel you want is from 1989+ M20's, the SINGLE MASS one. If it is huge & has 2 halves, it's not what you want. You cannot pick the wrong one, unless you are braindead or something. I ordered the bolts from Pelican Parts...they were just listed in the parts catalog there.

2002maniac · « **Reply #14 on:** April 05, 2006, 12:43:03 AM »

Quote from: asubimmer

my bolts came w/ it sorry I don't know the #ers

did you get your setup from bret?