shaving a flywheel

[Wh33lhop]

So, you are running a stock clutch etc, had your flywheel shaved down to 12-13lbs and no negative effects at all? Your idle is fine?

Just being thorough here because I want to do it right the first time!

I'm running a stock M50NV with a shaved-down flywheel, bathroom scale said it was 13lbs IIRC. No driveability issues at all, and it idles sort of funny but that's probably because I don't have an O2 sensor hooked up yet. ;)

Honestly, I'd rather have a lightweight flywheel with a lumpy idle and a cam than a regular-weight flywheel. You may be able to adjust your idle speed as well, depending on how you're tuning it.

[sweetride01]

As I mentioned, I think ~12lbs is fine with a stock cam, it's only when you start doing other things that mess with the idle that you're likely to start running into problems.

[aTron12]

Why stop at 15? Mine's at about 12-13lbs, I've noticed zero decrease in drivability.

So, you are running a stock clutch etc, had your flywheel shaved down to 12-13lbs and no negative effects at all? Your idle is fine?

Just being thorough here because I want to do it right the first time!

[erik325i]

If you're going to have it machined, take it down to 12-13. It would be silly to stop at 14-15.

[Wh33lhop]

Why stop at 15? Mine's at about 12-13lbs, I've noticed zero decrease in drivability.

[sweetride01]

That is helpful. So maybe I will stay at 15lbs in hopes of finding a good balance between performance and stability. I am running a stock cam...

Yea, I'm sure 14-15 lbs should work just fine for you...

[aTron12]

That is helpful. So maybe I will stay at 15lbs in hopes of finding a good balance between performance and stability. I am running a stock cam...

[sweetride01]

Yes, it does make the idle a little less predictable. In fact, with my Jim C chip and Schrick 284/272 cam, the idle is quite rough, and if I run with the AC on, the car can stall when I depress the clutch (the revs drop too quickly). But I'm sure that with a stock cam, this would not be a problem.

[aTron12]

Any negatives from going down to 12lbs? I have read that it is possible to throw one's idle off if the flywheel is shaved down too much. I'm thinking about going to 15lbs unless anyone thinks I should just go for lighter. I drive an '88 325is--daily driver. Thanks!

[sweetride01]

Haha, it seems so.

I got mine taken down to about 12 pounds, it's great now. Revvs so quickly :-D

[idanity]

iwoops, didn't realize this thread was ressurected from almost 20000years ago.

[idanity]

12 is the sweet spot for steel flywheels.




and the disc side




lets also talk about minimum thickness

4cyl. engines
84-85 = 23.5mm (.925 in)

6 cyl. engines
1984 = 25.0 mm (.984 inches)
1985-1990 = 32.0mm (1.26o inches)

open the Bentley to section 4 and page 58 to see the "a-step" cut (flange height)


weight can be ultra light, but remember to consider the warping.
steel is more durable than alloy, but my rule of thumb (or writs) is
never machine a flywheel thinner than the pressure plate (which would be hard to do)

when they machine it, also request all edges be rounded out.
also ask about the flange height (if they know, bmw doesn't specify what would reduce pedal throw to the point of not ever releasing the disc, and to perfectly release it at its minimal throw)
this is where experience comes into play.

ask you local track.
luckily, when i brought mine in, i already asked around, called around,and when i deliverd the f.w. i found 5 different posters of e30s...
thats a score.

to add.
if you can afford it, have your p.plate balanced to your flywheel when its all done.
they will have to mark both f.w.and p.plate so you can re-align them when you install it. but its worth it.

have fun.

[aTron12]

A little late here.. would you guys say that 15lbs is a good, safe weight to aim for? I am going to have this done next week since my flywheel is going to a machinist anyway.

[Ali//325i]

Ya My flywheel comes in at 12 lbs exaclty and was balanced and resurfaced at the shop i took it to. I could have gone lower but he said he wanted to keep it streetable at 12. My car runs great and i never have to use the brakes around town. They sent me a dual mass flywheel when i ordered it and i ended up getting it lightened, balanced, and resurfaced for less than it cost to buy a brand new flywheel.

-Ali

[ACHTUNG]

I just had aprox. 5lbs removed from my flywheel. It weighs aprox. 13lbs now.