M42 single mass VS M20 single mass conversion

[colin86325]

The M40 flywheel is the same as the M42 non-AC flywheel, which I fitted in my car.  I was able to find a brand new one that somebody was selling, but as a rule they'd have to be special ordered.

[romkasponka]

I swapped m20 flywheel on my E36 m44 engine and i have rattle on idle. It's annoying a little but I will try different gearbox before trying to ignore this sound. No any rattle I have with same setup on my E30 M42, but without power steering anf A/C. My E36 m44 gearbox seems is in good condition, but probably I will try to swap it to newer E46 gearbox, or probably before I will try to check oil level....

[Balleristic31]

Okay since I'm doing the m42 single mass swap, and haven't really seen many pics/evidence of this swap, I figured I should post my experiences.

Here's just the flywheel for now, stock, full weight straight from Germany.


Note: m42club has the m42 single mas weighs in at 22lbs , notice the actual weight..

[Balleristic31]

Update: got my clutch in from partsgeek.com. It was 107 shipped to my door and the brand was Luc. Came with tob, clutch alignment tool, and pilot bearings. Along with the clutch and pp of course. this brings my total cost so far to $257

I weighed the assembly as a whole an it came out to 32.5 pounds 20% less weight compared to dual mass setup. Tomorrow I get the flywheel lightened and balanced with the clutch

[ose30]

I used a special scale which gave weight 9.6kg.  I am currently doing a special wheel for Keith. We are going to get it about 8Kg. It needs to be done with special way; just milling it normal way will drop the weight about 500g. I had one wheel done with that way and got it balanced as well. Friend will re-program his CNC machine differently, so we can do it more radical way.
These wheels can be easily found here since it was used also with 316I & 318I with M40 engines. Btw, does dual mass flywheel starter work with M40/M42 singlemass flywheel ? If not, then i must put a euro M42 starter to Keith's package.

[keflaman]

I think we're good as far as starters go. BMW used the same one in several cars and markets. Part number 12411735524 superceded 12411715238 and cross-references to these models respectively:

http://www.realoem.com/bmw/partxref.do?part=12411735524&showus=on&showeur=on&details=1
http://www.realoem.com/bmw/partxref.do?part=12411715238&showus=on&showeur=on&details=1

[colin86325]

Yes, M42 dual-mass starter works with M42 single-mass flywheel.

[Gruelius]

bloody hell this is confusing!!! people saying you need the stock spacer, people saying you need a 3mm spacer, people saying just use the 325i TOB you will be fine....


Anyway my question.

325i single mass (assuming its not 323i as its heavy), spacer drilled off the m42 one, 325i single mass clutch kit, could i just use a longer slave? and do any m20 cars have a longer one? or will it work just fine like the nisse bloke said? theres about 6mm difference between the two throw out bearings.

and with the use of the spacer, wouldnt you worry about it not being perfectly flat and putting the flywheel on a slight angle?


**edit**

never mind, i did further research and now have a better understanding of the topic. i will measure the distance from crank face to the top of the pressure plate thingos to see how far out it will be and wether it needs a 323 TOB or not. will also try to avoid spacing the flywheel out.

[pungky29]

Here is another comparison after further research on BMW ETK software

E30 318i M40 Euro 5speed Getrag 240 with A/C, manufactured June 1990
Single mass flywheel p/n 11211739315 – 9.900 kg weight
Set clutch kit (inc. clutch cover, clutch disc & release bearing) p/n 21211223569 – 5.580 kg weight
Clutch disc p/n 21211223566 – 1.262 kg weight
Clutch release bearing p/n 21517521471 – 0.220 kg weight
Clutch release fork lever p/n 21511204229 – 0.515 kg weight
Starter motor p/n 12411735524 – 3.600 kg weight

E30 318is M42 Euro 5speed Getrag 240 with A/C, manufactured June 1990
Twin mass flywheel p/n 21211233550 – 12.250 kg weight
Set clutch kit (inc. clutch cover, clutch disc & release bearing) p/n 21211223571 – 5.036 kg weight
Clutch disc p/n 21211223492 – 0.834 kg weight for twin mass flywheel
Clutch release bearing p/n 21517521471 – 0.220 kg weight
Clutch release fork lever p/n 21511204229 – 0.515 kg weight
Starter motor p/n 12411735524 – 3.600 kg weight

Twin mass flywheel + clutch kit for E30 318is M42 Euro = 12.250 + 5.036 = 17.286kg
Single mass flywheel for E30 318i M40 Euro = 9.900 + 5.580 = 14.580 kg
Weight savings = 2.706kg

It is also interesting to note that:
1) Clutch release bearing, clutch release fork & starter motor for E30 318i M40 Euro is similar with E30 318is M42 Euro
2) The heavier weight of twin mass flywheel in E30 318is M42 Euro is compensated with the lighter clutch disc of E30 318is M42 Euro

Thus, to simplify the idea of converting twin mass flywheel on E30 318is M42 Euro 5 speed Getrag 240 manual trans with A/C, just swap using single mass flywheel from E30 318i M40 Euro 5 speed Getrag 240 manual trans with A/C together with the clutch kit.
No need to change the clutch release bearing, clutch release fork lever and starter motor

[DesktopDave]

That's the way I'd been thinking it should be, but it's a trade-off. Euro SM flywheels are expensive & difficult to locate secondhand. Late model M20 flywheels take a lot more torque with the additional benefit of being cheap & common.
 
I was curious, so I went down & weighed an old clutch.  This one is the old-style M20, with a slightly used clutch disc.  Including the flywheel, spacer, pressure plate, clutch plate & bolts it came to 35lb 3oz (16 kg).  My weight includes bolts but not the release bearing, and your quoted weights might include packaging materials.  So it's not apples-to-apples, but it's in the ballpark.  The M20 is far stronger and still weighs 1.25kg (almost 3lb) less than the stock DM clutch.
 
I wonder how much metal can easily be removed from the M40 SM FW?

[Warsteiner]

Here we go again..........I have used the M20 FW and stock 325 TOB with No issues whatsoever. I lightened the M20 to about 11lbs or 12lbs.

Just my .02

Cheers,
~Ralph

[Venom]

Has anyone used an m40 solid and how does it compare weight and durability wise?

[colin86325]

The M40 single mass is the same as the M42 single mass.

No problems with it in 4 years.  Though the idle drops a bit low when the AC is on and I'm traveling slow (like <5mph)  and then take my foot off the gas. I just have to clutch in more quickly than before.  That's all.