m20 flywheel conversion with m50 - Machining Question

[Mushroom Stew]

Hey all,

Which side exactly needs to be machined? Is it the side facing the engine or the side the clutch attaches to? And I've read that side needs to be machined approximately 7mm (no less), is that correct?

Any other advice/info on how to get the flywheel properly set up for a m50 is much appreciated. Thanks

[mtech325]

It's the side facing the engine that needs machining. I don't know the exact measurement, but just before the surface becomes flush with the ring gear. After machining, the flywheel loses 1-2 lbs from the process, so you get a slightly lighter flywheel as an added benefit.

As for making it work properly on the m50 otherwise, you'll simply need an m20 starter and an m20 clutch kit & flywheel bolts. Nothing out of the ordinary.

[Dagamus(NM)]

What is the benefit of using an m20 flywheel with an m50?

[mtech325]

Most people use them because their car started out as an m20 325i. They're also moderately light (~18 lbs) but not too noisy for a street driven car (particularly when paired with the stock m20 sprung clutch).

For sake of comparision, most e36 stock flywheels are in the 25-30 lb range and dual mass. So they're heavier, and more expensive to buy because their spring/rubber system wears out over time. The DMF is a wear item unlike a single mass flywheel which can be resurfaced by most machine shops when it comes time to replace the clutch. To be fair, the DMF makes the car very smooth and easy to drive, so it does have its benefits...but it'll cost ya $$$$.

[Mushroom Stew]

It's the side facing the engine that needs machining. I don't know the exact measurement, but just before the surface becomes flush with the ring gear. After machining, the flywheel loses 1-2 lbs from the process, so you get a slightly lighter flywheel as an added benefit.

As for making it work properly on the m50 otherwise, you'll simply need an m20 starter and an m20 clutch kit & flywheel bolts. Nothing out of the ordinary.

Perfect, thank you.

[Dagamus(NM)]

Most people use them because their car started out as an m20 325i. They're also moderately light (~18 lbs) but not too noisy for a street driven car (particularly when paired with the stock m20 sprung clutch).

For sake of comparision, most e36 stock flywheels are in the 25-30 lb range and dual mass. So they're heavier, and more expensive to buy because their spring/rubber system wears out over time. The DMF is a wear item unlike a single mass flywheel which can be resurfaced by most machine shops when it comes time to replace the clutch. To be fair, the DMF makes the car very smooth and easy to drive, so it does have its benefits...but it'll cost ya $$$$.

Interesting. Good to know, thank you.

[sneakyRedPanda]

I think I took an 1/8" off mine, probably don't need to take more than 1/16" though.

[CaffeinatedSoul]

I just did this swap a few weeks ago. I had nothing machined ffdp the flywheel. I just shaved the back side of the oil pan, cut the really long bolt wholes down to use short bolts, problem solved. 10 minutes with a grinder and $2 for short bolts.

[Mushroom Stew]

I just did this swap a few weeks ago. I had nothing machined ffdp the flywheel. I just shaved the back side of the oil pan, cut the really long bolt wholes down to use short bolts, problem solved. 10 minutes with a grinder and $2 for short bolts.

Interesting! I'm trying to visualize in my head what you did. Is it possible to take a picture does the attached transmission make it difficult to see what you did? How are you liking the m20 flywheel?