Flywheel heat vs. oil stain

[Dauner]

Hi everyone,

Rebuilding my 1989 911 3.2 and have a flywheel question. Approximately 25K miles ago the previous owner had a new flywheel seal installed during a new clutch install. Installation of the seal was not done properly such that when I received car there was steady oil leak.

Upon engine disassembly and clutch removal, the flywheel had oil and stains all over the flywheel, with black stains on clutch mating surface. I have two questions:

1. When a flywheel gets resurfaced, how much is typically removed?

2. The common concern with flywheels that are stained is the assumption that the flywheel has exceeded the temperature at which the hardness of the clutch mating surface may be compromised. hard and soft surface would obviously wear differently and eventually become an engagement issue. Where I work we do laser heat treating (among other things) and so I have access to a full complement of hardness testing equipment. If I test the surface in question and it is consistent across all portions of the surface, I would conclude that I don't have inconsistent tempering of the flywheel, and therefore should be able to face off the flywheel.

Pic of flywheel attached.

My conclusion is that the staining is due to oil getting on clutch flywheel interface and being worn in. The reason for question #1 above is hardness testing typically leaves a dimple on the surface. I assume I could have that dimple removed as part of the refacing, but curious on peoples opinions.

The testing costs me nothing. A new flywheel costs me $500.

Any thoughts greatly appreciated.

Thanks,

Mark

[Marc Bixen]

Dauner,
On 3.2 Carrera's with G50 trans you should not (Porsche says you can not) resurface the flywheel. I know there's guys who have tried, but... Some of the black towards the outside may be oil related, the inside "burn" marks are from slipping the clutch too much. "hot spots" If oil got into the friction disc, which is unusual, you'll have to replace that also.
Machine shops in general only surface to the point that the complete surface is cleaned and flat, or "true". Flywheels do warp over time. The worse the flywheel, the more metal needs to be removed.

[juanbenae]

have you tried wet sanding it with some #1000 or like grit body work paper? I can't tell from the photo if is the blue/purple signs of over heating one or simply the remains of burnt oil. more of a film than actual over heating damage.



the bright side of my theory is that the oil cut down on the slipping friction enough to save the flywheel....

[Dauner]

Thanks for the comments guys. I may try wet sanding a bit just to see what happens. I hadnt thought to critically analyze the color. Will post back if learn or observe anything interesting.

[gomezoneill]

Post a ad in the classifieds for a flywheel. I'm sure someone will have one at a reasonable price.

[Dauner]

Marc, Do you know why these particular flywheels are not candidates to be resurfaced? I really couldn't find any info online last night regarding materials, manufacturing process etc. not sure if they are cast or forged. not sure if they are hardened. the gear teeth may be induction hardened.

Good idea on classifieds. the 87-89 ones don't seem to come up very often at all.

thx

[T77911S]

those are HOT SPOTS on the flywheel from improper driving.
you probably had some clutch chatter when accelerating from a stop.

i lightly sanded the flywheel on my 325is with a flat hard sanding block and fine sandpaper.
maybe 400 or 600.
you can try that or have the flywheel cut.

not from oil

[juanbenae]

he stated there was a leaky flywheel seal.

[eastbay]

150 grit on a vibratory sander is what you want to use if you are going to sand it.

[Marc Bixen]

Dauner,
This was the first hydraulic clutch 911, and I believe it has to do with the extremely tight tolerances and the angle of the clutch release fork. There may be a possibility of the fork bottoming out against the case. Additionally. I once saw a 3.2 flywheel that someone had surfaced, On the outer circumference of the flywheel there is a TDC indicator post for the reference sensor, that threads into the flywheel. and on this particular, re-surfaced flywheel, you could see the threads of the TDC marker half machined through on the surface. Basically, no Porsche flywheels from 1987 through the current dual mass flywheels should be resurfaced. As the other guys have said, some times they can be saved with light sanding, or a Scotch disc, but no machining.

[T77911S]

you need to keep the surface as flat and square to the mating surface as you can. IE, dont concentrate in a single area.

hot spots, it will cause clutch chatter. its form burning the clutch or slipping it too much.
heat a spot on metal and you will see it turn blue, same thing when the clutch heats up the FW.
people that dont know how to drive.
got a guy here at work with a brand new WRX with a burned out clutch in it.

[Lyle O]

From the workshop manual...

[proporsche]

Mark..if you put your hand on the surface it is most likely smooth right?
Just the marking..and what you call oil stains...to be honest i have seen much worse 87-89 flywheels then this one.
Clean it a little bit take it easy with the sending so it does not ended up with high and low spots.Then reassemble ......with new press plate and new disc....you will be fine...
Ivan