flywheel machining

[OG911]

'85 3.2

flywheel is at the shop for resurfacing prior to reassembly- machinist asks whether the pressure plate mounting surface around the outside edge of the flywheel needs to be shaved by the same amount as the disc area-

anyone?- thx

[john walker's workshop]

Of course.

[PeteKz]

John, I understand that the measurements should be kept the same. I just want to ask how critical that is. If the flywheel cleans up at say, .005", that is far less than the wear of the clutch disc over its life, so it seems to me it wouldn't matter. If significantly more, then it I think it would matter. What's your experience?

[john walker's workshop]

You pays yer money and you takes yer chances. It's just the normal way to do it. YMMV.

[Jeff Alton]

I am with John. It is just how it is done, why risk an issue. Any competent machine shop does it this way....

[PeteKz]

If I was delivering a flywheel to a machine shop, I would tell them to do both surfaces. The cost difference is minimal. I was asking a hypothetical question. For example, If I had a flywheel that had been machined on one surface, but not the other, should I even consider using it? At what point would you say don't think about it?

[OG911]

The expense isn't any part of the consideration. It occurred to me that porsche might have put some additional meat on the pressure plate surface precisely so that it could be machined as part of clutch change without reducing the attachment surface and still function as designed.
Is it logically different than simply having the clutch disc wear? Idk

[gled49]

The PP mounting surface is the same as the flywheel disc surface, it’s all flat, you machine the flat surface.

[aasco]

You have to consider the length of the diaphram fingers at the TO which multiply the ratio by as much as 5 X due to the fulcrum under the pressure ring.

[Henry Schmidt]

An inexperienced enthusiast comes here asking a question about the right way to do a job, gets the correct response then pushes for a different answer....
John brings 40 years of Porsche expertise only to be dismissed.
The best answer yet: "You pays yer money and you takes yer chances".

[Turbo_pro]

Originally Posted by aasco

You have to consider the length of the diaphram fingers at the TO which multiply the ratio by as much as 5 X due to the fulcrum under the pressure ring.

I'm not sure who is behind this iconic moniker, but welcome to the forum.

[OG911]

inexperienced enthusiast?- that's funny- have been turning a lot of wrenches on a lot of cars for a lot of decades- it may be my first 911 flywheel, but so be it- it is worth asking a question of the community- the fact that the flywheel surfaces are different heights makes an experienced guy wonder!-
please accept my apology for inquiring further

[aasco]

Thank you thats very kind, I joined to post pictures of some things I have to sell in the marketplace and they required some forum activity.
Great Quote by TS

[phunt]

I have built a few engines as well and this is my first Porsche. I think this is a pretty simple engine design.
If the machine shop asked me the question of do I machine both surfaces? I would say thank you and go somewhere else.
Here is a 3.2 and a 3.0 flywheel. Even though the 3.2 has a grove or channel between the pressure plat and disc surfaces they are on the same plane or levels so doing one without the other seams difficult.
I stick with the KISS principle and have pretty good results.

[brighton911]

Yes, I too was surprised that a shop that does flywheel grinding would even ask that question. If only the surface that the disk rides on was ground, the pressure plate would have less "clamp" on the disk. So that is why and always - the pressure plate mounting surface is cut the same amount. Simple

[Flat6pac]

Factory recommended not cutting the Carrera flywheel.
Bruce