Flywheel question....

[ksollinger]

Hey All,

So the motor is finally out of the 76 and Im paitiently waiting on my new clutch and random parts to get it back in. When I pulled the original motor the clutch was stuck to the flywheel and upon removal I noticed that there was light surface rust across the flywheel (see pics). I took some light sandpaper to see how bad the rust is and it came off relativly easy but my question is should I get it professionally resurfaced or is this something I can do on my own? There are three seperate rings on the flywheel and the center ring sits lower than the other two, is this normal? This is my first clutch replcement I've done and just want to make sure I do everything right.

Thanks in advance for everyones advice!

-Kelly

[Mike Self]

that mates with the clutch plate. So long as it's smooth and not grooved or scarred (like a worn-out brake disk), and the mating surface still stands proud a mm or so from the remaining surface, you're good to go.

You really don't even need to sand the light rust off, as it'll be polished off the first time you drive the car--kinda like (again) brake disks. But it certainly doesn't hurt to do so.

While the flywheel is off the car, carefully inspect the flywheel teeth for badly worn or missing ones; if the ring gear is bad, now's the time to replace it.

cheers

mike

[c.d.iesel]

a.) should I get it professionally resurfaced = YES

b.) or is this something I can do on my own? = NO - not in that condition

the clutch friction plate surface is f_ _ ked-up -

have it 'skimmed' by a machine shop - if you don't

you'll have a very unhappy clutch function.

[TobyB]

I'm with CD on this one- there's a groove in the friction surface that's not

supposed to be there. If you were stranded in the middle of the desert,

it wouldn't matter, but since you're doing it right, spend the $40 to

get it surfaced. And it should have a .5 mm step for the friction surface.

t

[Guest gliding_serpent]

I am going to throw in my numbers as I recently had my flywheel refaced.

From my records (forum, and BMW 02 restoration guide by M. Macartney), it has a stock 0.5mm raised lip (book says 15 thousand's of an inch or 0.381mm). Some forum members have mentioned 1mm working well. I went with 0.5mm.

Key: BMW advised not to machine more than 0.012 inches (0.3mm) off of the face of the flywheel (mine needed 0.010...). That means no more than 12thou from where the clutch driven plate sits, and 12thou from where the pressure plate sits. Why, because after 12 thou you go beyond the hardened portion of the metal on the flywheel face and the clutch will wear faster. You can do it, just don't expect the lifespan it got pre-machining.

Finally, the minimum thickness should be no less than 14.5mm according to BMW. Why? Any thinner and you will need to machine the same amount off where the flywheel bolts on to the crank or you will get some serious grinding when you engage the clutch. You will also compromise integrity.

Keep these numbers in mind if you choose to generate a 1mm step.

Good luck, machining is precise stuff! Do it right.

[ksollinger]

So from the recomendations I got I took the flywheel to a local shop and had them resurface it...

There is no longer a "step" in it and it's been ground completly smooth. The shop that did it couldnt tell me how much surface they took off because the tech was no longer there for the day. Im hoping that it will still work even without the "step" in it. Please tell me I dont have to by a new flywheel now because they screwed it up!

[Preyupy]

Take it back to them and have them cut the step back into it. You are loosing clamping force by not having it. They should know better.

[ksollinger]

Since the step is no longer in it is there a reference that I can show them stating what the dimesions of the step are? How deepth, width, width from center etc?

[c.d.iesel]

member 4x2 wrote :

Yes, the outer "ring" that the pressure plate mounts to.

Shiny part = friction area

Dull part with -0.55 (mm) written on it is the step.

and Billy Williams wrote:

and do as Bill did, clean the timing marks

on the edge of the flywheel and wipe WHITE

paint into the marks so you can see them

when you use a timing light when you get it

running again

[ksollinger]

My original flywheel had a step down, not a step up? The .55 is the depth that needs to be removed correct? What is the proper width of the .55 depth?

Thanks!

[Guest gliding_serpent]

Machining is hard on the nerves eh?

Assuming symmetrical levels of wear of both levels of the step prior to all of this, one would expect the step to be in the 0.3-0.5mm region...i.e. stock (15 thou). For that step (the pressure surface) to have been removed, we can assume at least that much was taken off to get a flat flywheel surface. That brings you beyond the 0.3mm (12 thou, 0.4mm in the link below) advised threshold for shaving (remember, we are now into softer metal), at least for the "center" step or friction surface. So you may not need a new flywheel, but again, don't expect this one to last as long.

Now, before you get that step added back in, get them to measure the flywheel thickness (at the friction surface... the smooth surface they just created, but near the center). If it is less than 14.5mm I would just look for a new flywheel.

Good luck. I am sure it will be fine.

EDIT. Step down, not step up. i.e. the outer portion will be lower. Take .5mm off. I don't know how far "in" the step is.

The above flywheel with the 0.55mm is from this thread http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/start,0/t,349984/topic_view,flat/

They were talking 215mm flywheels which were the same for a few different models.

2002 1969-1972: 228mm flywheel

2002 1973-1976: 215mm flywheel

2002Tii 1972-1974: 228mm flywheel

E21 320 1977-1983: 215mm flywheel

E30 318 1984-1985: 215mm flywheel

[lilmo]

So from the recomendations I got I took the flywheel to a local shop and had them resurface it...

There is no longer a "step" in it and it's been ground completly smooth. The shop that did it couldnt tell me how much surface they took off because the tech was no longer there for the day. Im hoping that it will still work even without the "step" in it. Please tell me I dont have to by a new flywheel now because they screwed it up!

They owe you a flywheel. Probably an honest mistake by a younger tech, but if you told them what car the flywheel is from, they can look up the spec. Even the tiniest shops that do flywheel work have thick binders full of flywheel info. Some even have access to the internet.

Take it back, talk to the owner and the tech that did the work. Be a good learning experience for all involved. Do you take it to a mechanic who advertised flywheel resurfacing, or did you go to a true machine shop?

Then again, it might be fine for 100K plus on a DD. I'd just hate waking up each day wondering if I'm gonna have to yank the tranny next weekend because I gave my machinist a pass.

HTH

N

[ksollinger]

More flywheel questions.....

So I laid the old clutch disc on the flywheel to get an idea of the "step" spacing from the edge and plan on taking this with me as referance as well. So just out of curiosity I placed the pressure plate on top and there is a significant gap between the two surfaces. I dont recall 100% what it looked like when I pulled it but this seems wrong to me? Also just so everyone knows this is off a 76 and it's a 215 flywheel.

Sorry about all the questions but Im just pissed! Everytime I make headway getting one step closer to driving I get another set back!

[Guest gliding_serpent]

13/16ths is what I get... just over. But this was NOT with a precision measuring instrument so I would wait for official numbers before acting. I suspect this number should conform to your second image in the above post.

[allbim]

If you have a 215MM disc, the raised portion of the flywheel (friction surface) should have a diameter of no less than 215MM. I would make it 2 mm bigger than whatever the disc diameter is.

There is nothing critical about that. I just measured an unmodified flywheel and found the friction surface to be 1MM (.04") above the pressure plate mounting surface. Don't worry about the flywheel getting to thin.

If you ever look at a flywheel that has been lightened for racing, you'll know what I mean. Also, I am presently using a flywheel that has no step and it works very well.

I would not blame the machinist for taking to much off, because there isn't one in the world who would take off more than needed to clean up the surface.

When all the machining is done, make sure the dowel pins are re-installed.