More about flywheel options for M40, M42 and M44 engines

By · May 20, 2014 · 2 comments

As I need to replace the clutch in my supercharged 1998 318is I have been looking into what options there are for a stronger and preferably lighter clutch.

M42/M44 dual mass flywheel and clutch

I presume my car has the original dual mass flywheel and clutch so I could go with just a new clutch kit. However, I have concerns that the flywheel may not be in good condition and it is not advised to have dual mass flywheels machined so there is a risk to just changing the clutch.

I would also prefer to replace the clutch with one that could handle the extra power from the supercharger better. There are a few choices in stage 1, 2 or 3 clutch kits for M42/M44 powered BMWs on eBay USA which is another option, but again I would prefer to replace the flywheel as well.

M40 solid flywheel and clutch

I looked at the M40 flywheel and clutch kit option, which is a bolt in replacement and requires only the M40 flywheel and shorter bolts, and an M40 clutch kit. This is a little lighter (1.72 kg) but the clutch is the same diameter (215mm) as the original so is not going to handle the supercharger any better than the original.

I did the M40 flywheel swap on one of my previous 318is's and I can't say I noticed much or possibly any difference in performance or driveability. I did notice a small increase in the amount of vibration and harshness, but really only when at low engine speeds under load, for example when taking off from rest uphill.

Valeo solid flywheel conversion and clutch

Valeo make a solid flywheel conversion kit for the M42/M44 but it is designed as an OE replacement and the flywheel is comparable in weight to the dual mass unit. I can't find any specifications but I presume it is the same size as the original, although one Australian retailer implies it is 235mm (they could not confirm to me if this was true). Assuming it is the same weight and the same size then this seems like an expensive alternative to the M40 flywheel swap. The Valeo part number for the M42/M44 is 52161203.

M20 solid flywheel and clutch

The solid flywheel from the M20 engine, usually the later model E30 325i, seems to be the most popular upgrade. Not only is it lighter (and can be lightened further) but it is also larger (228mm). My issue with this is that it is a more complex swap - you need an M20 flywheel, shorter bolts and an M20 clutch kit. But as the starter/ring gear is different you then either need to swap the ring gear, use an M20 starter (not all fit) or swap some of the M20 starter parts with the M4x starter. Then there's confusion about which throw out bearing to use - the majority say get one from an E21 323i but some say the one that comes with the M20 clutch kit works fine. Lastly you either need to remove some material from the flywheel or remove and fit the spacer from the M4x flywheel (riveted on and needs one hole drilled larger to fit) to stop the M20 flywheel from jamming against some bolts on the back of the engine.

M50/M52/M54/S50 flywheel and clutch

I have read about another option, apparently the M50/M52/S50 flywheels and clutches fit too. There isn't many people talking about this but the ones that are use an aftermarket solid flywheel from an E36 M3 3.0 with the clutch kit from the same model. The advantage is that the clutch diameter is 240mm and obviously designed for the M3 so should be up to extra power of a supercharger. The ring gear is the same so the starter does not need to be changed. One person mentioned they needed to fit the slave cylinder from the M3 too as the original didn't handle the extra pressure. The negatives of this are that the cost of M3 parts is generally much higher (clutch kit is around twice the price).

Apparently all M50/M52/M54 flywheels will bolt straight on without any modifications. All use either a 228 or 240mm diameter clutch plate. Most of the M50/M52/M54 flywheel and clutch combinations weigh around the same as the M42/M44 parts, and some are a little lighter. There is also apparently a conventional flywheel available for the early M50 (E34 525i and E36 320i) without air conditioning although I doubt any of these made it out of Europe and the weight is similar to the dual mass flywheel/clutch combination.

Update: I don't know if the flywheel/clutches from models with the ZF gearbox (eg. 328i) do fit or not. The 228mm flywheel/clutches from the M50 320i/325i and M52 323i, which use a similar Getrag gearbox to the 318is, seem like a safer choice.

M43TU dual mass flywheel and clutch

Recently I discovered that the M43TU engine fitted to the E46 318i (and maybe some E36 Compacts) uses a 228mm clutch plate. The earlier M43 engines can use the same clutch and flywheel options as the M40/M42/M44 so there is a good chance the M43TU flywheel will fit the M40/M42/M44 too. The downside is that the flywheel is a dual mass type so there wouldn't be any weight saving with this swap. I am yet to confirm that it is even possible and there certainly doesn't seem to be any discussion about this online.

BMW M43TU flywheel and clutch

Here is the weights of the various options:

FlywheelClutch KitTotalTotal (my scales*)
M42/M44(P/N 21211223550) 12.25kg(P/N 21211223571) 5.04kg17.29kg16.5 - 17.0kg
M40(P/N 11221739315) 9.99kg(P/N 21211223569) 5.58kg15.57kg14.8 - 15.2kg
M43TU(P/N 21207508409) 12.87kg(P/N 21217523618) 5.24kg18.11kg
M20(P/N 11221706573) 8.5kg(P/N 21211223102) 6.98kg15.48kg
M50 (325i)(P/N 21211223593) 11.134kg(P/N 21211223546) 5.920kg17.05418.0kg

*My scales is my own measurement using simple bathroom scales.

I am still investigating the options so will keep this page updated.

Have you changed your flywheel and clutch, or do you know anything else about these options? Please leave a comment below to share your experience.

Update 1 April 2015

I ended up buying a second hand flywheel and clutch from an early M50 engine. I paid A$150 and as the clutch plate was in very good condition I decided to use that rather than buying a new clutch kit. I did have to get a new throw out bearing though. Read more in my post.

Update 20 May 2016

I found a company in Sydney (Australia) that sells a lightweight flywheel for the M42, M44 and M50 engines for a very reasonable price. They say it uses the original M42/M44/M50 starter motor. You use a clutch is for the M20 engines (228mm), including any aftermarket options with a higher clamping force if needed. Weight is 3.2kg (7lb). See RHD Engineering. Shame I didn't know about this before I fitted an M50 flywheel and clutch.
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Comments (2)

# Posted by Charlie · March 9, 2016

Very interested in this subject if you could update it would be much appreciated


# Posted by John Avis · May 19, 2016

Hi Charlie. See my update about a light weight flywheel option from RHD Engineering that I would definitely look into if I hadn't just fitted a stock M50 flywheel/clutch to my car. For US$219 it looks like a great option and you can use a M20 clutch kit.


John Avis
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About me
John Avis I am a bit of a 3 series fanatic, having owned a couple of E30s and a few E36s, plus a few parts cars. I like the combination of the compact size, good performance and handling, and that they are more sports sedan than an impractical and extrovert sports car. This blog is a place to share my experience and knowledge.

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