m20 flywheel lightening

[TheMeathead]

hey guys

Ive got an m20 flywheel im going to get lightened, the question is by how much??
weighed on its own its just over 8.5kgs
Now i have seen people say take them down to 7-6.5kgs, is this just the flywheel on its own or the hole clutch assy??

any advise would be great

ant

[eko]

Mine is lightened to 7kg(flywheel only).
Heard of people going much lower than that though,5kg +.

[Sjoerd320i]

I believe Dan does them at 5.3 kg's?

[e30-EVN]

I took mine down to 6 kilo's (flywheel only). Felt the difference straight away.! When it comes out next time to change box combo I'm taking it down to 5.1 kilos

[Gruelius]

flywheel only.

usually you lighten the fly then balance the fly with the pressure plate bolted on.

[e30-EVN]

flywheel only.

usually you lighten the fly then balance the fly with the pressure plate bolted on.

what?? i had the flywheel lightned not the clutch plate
nobody has asked about balancing, just how much weight to take off the ''flywheel''.!!

[DanThe]

5.3kg is plenty and about the max id go to, done loads for E36ers and zoners now

[e30-EVN]

was that one in the pic you sent me via text 5.3 dan?? i cant remember

[DanThe]

Yeah it was

[e30-EVN]

thats the one. however, even though next time the box comes out i will be going this far... 6 kilo's makes a nice difference to the way the engine feels. but then more is better

[TheMeathead]

cheers guys

ive had one machined down to 6.5kg's, gonna put it on the m20 before i do the m50 swap and see what happens ;)

cheers ant

[HairyScreech]

Disclaimer -Just curious and not doubting the work in anyway as i know your like me on these things.

Dan, your lightened flywheels, have you looked at the change is stress in the flywheel?
And have you given one hell? i assume you run one on your alpina m5x in which case it has been suffering plenty of torque.
Do you have any idea of the safe RPM of them? (Do we have any idea of the safe rpm of a standard one?)

Just asking as in the near future i may be after one for the 2.8 and i am thinking it may be revving a significant bit more than the 6500rpm stock redline.

[DanThe]

Not looked at anything like that, I just have them turned down no more than the minimum thickness that is already there, I dont have one on my Alpina but I do have one on the M52B30 track car with a 5 paddle clutch that gets its fair share of abuse, there are also plenty of E36 328i track cars and 4 pot compact track cars etc with the same flywheels.
It would be good if you could work some numbers out though

[e30-EVN]

mine is 6 kilo's as said above, on an m52 with a 7k rev limit that im not afraid of
handling the abuse so far so good

[HairyScreech]

Not looked at anything like that, I just have them turned down no more than the minimum thickness that is already there, I dont have one on my Alpina but I do have one on the M52B30 track car with a 5 paddle clutch that gets its fair share of abuse, there are also plenty of E36 328i track cars and 4 pot compact track cars etc with the same flywheels.
It would be good if you could work some numbers out though

Funnily enough i have an accurate cad drawing of the stock m20 one, so if it is as you say taken back flat across the back where the dip is then i can make that change pretty quick and see the projected mass.
The program allows a centrifugal load, a torque loading and a combination of the two, so i will have a look and see how they compare.

The torque load would be felt worst at the bolts/thinnest section the centrifugal at the edge, so the lighter one could potentially fair better.

I will have a look once i have this work out of the way.

[DanThe]

Cool, looking forward to the results.
Worth pointing out the early M20 factory flywheels were about 6kg also

[suchy]

I've run one on my b25 for over 7yrs now with no ill effects. I never redline mine though!

[DanThe]

Mine is used mostly between 5k and 7k revs!

[HairyScreech]

I can currently see the possibility of getting to 8k, which is why i'm a bit twitchy about my ankles. (very light b28 reciprocating assembly and no oil pump nut worries.)

I quite attached them and would rather have feet that a light flywheel (or even a stock one).

Early M20 flywheel?
Do tell, i never knew there was a difference.

[DanThe]

Check it out, 6.3kg - http://bmwfans.info/parts/catalog/E21/S ... _flywheel/

[HairyScreech]

I see, its similar to the lightened ones having a uniform thickness across the back.

[e30rapidic]

I took my M20 flywheel down to 11lbs (roughly 5 kilos) with my S50 swap and its great. Only drawback is that I had to bump the idle rpm's up so it wouldn't stall.

[HairyScreech]

Just working on an FEA now.

[Jozi]

Cool, looking forward to the results.
Worth pointing out the early M20 factory flywheels were about 6kg also

I have one for the m52, can weigh it if anyone wants to know the weight?

[HairyScreech]

ok, used my stock m20 flywheel drawing from the v8 flywheel stuff and span it to 8000rpm.
Didn't have the pcd of the bolts to hand but 70mm diameter fit nicely in the center of the flat bit where the holes are supposed to be, however it shouldn't make huge odds.

Stock flywheel calculated to 9.85kg, extra mass may be because the ring gear was drawn solid.
stress was 195n/mm^2 by max principal and 173n/mm^2 by von mises

Skimmed flywheel was flat across the back maintaining the thinnest section out to the ring gear, a 6mm radius at the edge and flush with the ring gear like dans.
Stress was 137n/mm^2 max P and 121n/mm^2 by von mises.

So the lighter flywheels are actually better at higher revs despite the thinness of them, infact even on the stock flywheel the worst stress is near the bolt holes.

I'm not 100% what the material is but assuming an average decent grade of steel then i can't see any fatigue issues using either wheel at 8000rpm.

When i get some time i will do an FEA with 240lb/ft chucked in along with the centrifugal loading so we have the worst case for any N/a I6.

[DanThe]

Good to hear that, id always have thought the most stress would be around the bolt holes, so dont forget to fit the washer plate before bolting the flywheel down

[Dirty6]

I'm not 100% what the material is but assuming an average decent grade of steel then i can't see any fatigue issues using either wheel at 8000rpm.

They are Nodular Iron, not steel. Not sure I'd want to spin one to 8k, but am happy to spin my 6.2kg to 7.

[HairyScreech]

Yes, i have 3 grades of modular iron in bad, g25 - 40 - 60.
G40< would be fine with these stress levels so if we can find out exactly what it is then i can say for sure.
However at this stage i would err on the side of it being ok.

[brucey]

Good to hear that, id always have thought the most stress would be around the bolt holes, so dont forget to fit the washer plate before bolting the flywheel down

So that's what that washer bit was for!

I've been reading around about that, some have been using it as a spacer between the fly and the crank as an alternative to machining

I might have to go back and put that in then

[e30-EVN]

I might have to go back and put that in then

ummm, yes.!

[DanThe]

So that's what that washer bit was for!

I've been reading around about that, some have been using it as a spacer between the fly and the crank as an alternative to machining

Great idea that....