Flywheel specs

[bravo 35]

I sent my flywheel to BNT for machining and the useless buggers cocked it up. The m20 flywheel has two surfaces on the face pointing toward the gearbox - the surface the clutch makes contact with is rasied slightly from the outer surface the pressure plate bolts to to increase the loading of the pressureplate on the clutch disc. BNT ground the flywheel down so that it was dead flat all the way accross.

I would have thought it was patently obvious to any dumb cluck that the surface in need of maching was simply the raised area the clutch disc contacts, but obviously not as these "experts" coyuldn't even do it right.

My question is, how much is the rasied area supposed to be above the flange surface (that the pressure plate bolts to). As I am going to have to get them to redo it.

Also, my bentley tells me that the minimum flywheel thickness is 25mm. I don't know what it was before machining, but it is now only 19mm. Is this because they ground it down by this much! or are there different flywheels than listed in the Bentley?

Basically what I am asking is, am I ringing them up to give them a bollocking and demanding re-machining, or am I chasing them for a new flywheel as they have wrecked this one?

Cheers

Edited October 15, 2006 by bravomikewhiskey

[Carl 3]

For your sake i'd get them to get you a new one as if it's too thin it'll fail, but ask Grant (325Grant) what happened to his one he got machined down

Did you ask tell them about the minimum thickness?

[bravo 35]

I beleive it is up to them to know that kind of thing. When I got my brake rotors machined, the machinist looked in his book of specs and told me that they were/were not within limits and whether or not he could machine them or that I needed new ones. Until I got the flywheel back and noticed that there was something different about it I didn't even know about the raised area or minimum thickness.

I just noticed it didn't look right so did some research, checked my manual and then even asked someone I know who all confirmed that it was not right and had to be either fixed or replaced.

The machinist at BNT should have looked up the specs, or at least wondered to themselves why the flywheel wasn't flat all the way accross. If they do this all the time they should know there is a minimum thickness for a flywheel, and lloked up the specs for my one. They are the experts, not me.

I'm happy to demand a new one, but want to make sure that there were no thinner flywheels for the m20 before I tell them they can't just re-machine my one. (I want to get my facts straigh in other words).

Cheers for your fast response carl.

[bravo 35]

Spoke with 3 people at BNT the last one being the workshop person in charge of flywheel machining. Their book tells then it should be flat and so that's what they did.

I argued the toss and they said if I can prove them wrong they'll sort me out.

I spoke with some guy at Bavarian (just a young floor mechanic) who didn't know but said he was looking at an m20 flywheel that was flat.

I spoke to Ross Lamb of BM Workshop - the friendliest, most helpful person ever, and he agrees with me that they shouldn't have flatened it and that whatever they took off the raised area should also be taken off the flange area to keep the relationship the same.

I spoke to Eugene (Ross Lamb gave me his number) at tradeparts who seemed to think the lip should only be a fraction of a mm (it is 3-4 from memory/pics on the internet/as measured for me by e30stz ion a spare he has) and that it wouldn't make a diff. if its a fraction of a mm he may be right but I suspect he's wrong as he thinks the lip is so small. For what its worth he referred to BNT as a pack of f**kwits...

I spoke to the local BMW service agent - they agree there should be a lip.

I spoke to a mechanic I sometimes use that did his apprenticeship on e30's with BMW in the 80's. he agrees with me.

What do you lot think I should do now - go back to BNT and tell them this or does anyone have any further ideas. I beleive I should be demanding a new flywheel (or at the very least a secondhand one machined correctly). But if it doesn't matter then all I'm doing is wasting everyones time and money.

Ideas?

Edited October 16, 2006 by bravomikewhiskey

[Guest Ken]

You said... "Their book tells then it should be flat and so that's what they did."

Did you get a good look at their documentation - does it actually say that? Also, in this age of accreditation and accountability etc. do they have a sales/service charter? There may be some wording in there that states that they WILL "put things right".

Personally I would avoid getting too "heavy" and persue your case with clear, concise documentation rather than arguing anecdotal "facts". People tend to be more relaxed when confronted with an open "let's get around the table" type approach.

For what it's worth!

Ken.

[bravo 35]

Yeah I have been speaking with the guy in the workshop. They are happy to remachine it to put it right, but need to know what the specs are. No-one seems to know what they should be.

Thay have "bitten the bullet" so to speak, but nowhere can anyone find anything which gives the specs for the step. I could just choose an arbitrary amount an have it put in (say 2mm).

The other thing is, what are the cahnces of the flywheel failing if it is fixed now it is thinner? Its a solid steel flywheel, and should stand up to a fair bit of machining, but if its going to end up too thin they need to replcae it for me. I'd be happy with a secondhand flywheel machined correctly, but need to find out if mine is fixable first.

Anyone got one they can put a micrometer on for me? One of you tech-heads/gurus out there (kerry, conrad, anyone?) must know something about this.

[Guest Ken]

I've got a "lightweight" one via HARTAGE that has a 0.3mm step (verniers not DTI) and a thickness of 22.7mm (not including the step).

K.

[bravo 35]

This pic shows a flywheel with quite a step on it

I can't for the life of me remember how much of a step mine had to start with. The above flywheel is not off an m20 but looks very similar.

I'm surprised no-one here knows.

Bloody frustrating to say the least.

[Guest Ken]

Just a thought and any "real" engineers out there may well dismiss this but my flywheel has drilled indentations around the periphery for balancing purposes. Therefore, would providing a raised portion allow you to resurface without cutting into the area with the balancing indentations? If so, the height of the lip shouldnt really matter, so long as the overall thickness of the flywheel is within whatever specifications you can find.

[westy 614]

Try calling Autoclutch 09 8493737 ,they are the experts.

Fwiw ,when they machined mine they machined the mounting face and the friction face ,I presume they remove the dowels to do this??There is a definate step,but its probably less than a mil.

E. heres a picture for your viewing pleasure

Edited October 16, 2006 by DirtySix

[kiwipetrolhead 1]

Try calling Autoclutch 09 8493737 ,they are the experts.

Fwiw ,when they machined mine they machined the mounting face and the friction face ,I presume they remove the dowels to do this??There is a definate step,but its probably less than a mil.

Heye, you could always ask a wrecker if you can borrow a flywheel, then if it does have a lip, take it to BNT and show them. They can't argue against hard evidence like that.

Good luck

Paul

[Guest Spargo]

Does this help G-man?

[bravo 35]

upside down sam.

Well I've spent 2 hours on the ph today trying to discover the answer I want. Basically I'm down to two questions:

With my flywheel being 19mm is it now too thin to machine further?

If not - how much lip do I need to create when its machined further?

Cheers

[bravo 35]

Eventually ended up ringing somewhere in S.Africa that Will (Topless) dealt with when he was over there. They knew off the top of their heads. Lip is .3mm (Much less than I thought). The consensus of opinion of the clutch manufacturers and mechanics I talked to was the lip (even that small) was quite important. All of the flywheel machinists seemed to think it didn't matter. In any case it is back at the machinist being re-machined to spec.

As far as thickness goes, I decided to double check the thickness (as I had an "assistant" do it for me). Turns out not only is my old man a blind old bastard, but even though he was brought up on it he can't read imperial and it wasn't 16th's of an inch on the scale, but 32ths, so that made a huge difference and the flywheel is actually 23.5mm thick not 19mm. Dad, you're fired you old, blind, twit!

Anyhow, the min spec in the bentley is 25mm, and so I'm going to live with it as 23.5mm will withstand (IMO) most of the punishment I intend on delivering without warping and it means the flywheel is a whopping 30 grams lighter - badass.

[kiwipetrolhead 1]

My '83 e21 323i flywheel has a slight lip - my guess is that it's about 3 thou although I didn't measure it and it's back in the car now (but I have a very good 'eye-crometer'). Might be the same flywheel as an e30.

I have photos if you want them (three views, some close-up)

Paul

[bravo 35]

All sorted thanks Paul as per above reply. Car has been manual and mobile for 6 days now.

When I manual'd the 320 it got a bit of a performance gain, and expected a similar difference on the 325. But the performance gain on the 325 is just phenomenal! Ass-dyno of course. Revs up way quicker without that damn heavy torque converter. Having a lot of fun wearing out my rear tyres the last few days. Cool.

[kiwipetrolhead 1]

All sorted thanks Paul as per above reply. Car has been manual and mobile for 6 days now.

When I manual'd the 320 it got a bit of a performance gain, and expected a similar difference on the 325. But the performance gain on the 325 is just phenomenal! Ass-dyno of course. Revs up way quicker without that damn heavy torque converter. Having a lot of fun wearing out my rear tyres the last few days. Cool.

Good stuff, sounds like you're having a ball!

Paul