help with 71 flywheel

[cjmurph]

Need some advice. I've attached a pic of my flywheel. Finding a machinist nearby that has any experience with porsche is not going to happen but I realize if I can provide the specs they can do the work.
In my flywheel pic you will see a yellow line. It is a step that apparently is machined. I need to know the specs on this step (how high). I've had two seperate machinists dispute that it is indeed a step and not simply wear on the flywheel. They were more than willing to machine it flat.
I also need to be able to tell them "what radius to cut the flywheel/clutch contact area. Example, if my clutch is 225 mm then should the radius of machined surface be 226?
I've read flywheel threads until my eyes bled. Most years apparently don't have the step that I'm seeing on mine.
Any spec advice would be greatly appreciated.

[andrew15]

My factory workshop manual shows that the flywheel is flat across your red and blue areas with no step at the yellow mark. It also shows that min thickness is 8.5mm. I'll take a picture of the page in about an hour (camera battery dead)
Regards
Andrew M

[ddubois]

I recently machined my 71 flywheel. There is no step. As Andrew will provide, the workshop manual min thickness is .335". Any reasonable automotive machine shop can do this, they will machine across the entire surface. Mine cost $35 and it works fine. What you will have to be careful with is reassembling with I assume your new disc/PP/TOB, and the correct spacer/spring on your release fork due to new disc and flywheel thicknesses. It's difficult to explain, but search and you will find plenty.
Oh, and you are replacing those expensive flywheel bolts?
Also be careful if you buy new PP bolts. Mine from Pelican had a taller head than stock and interfered with the bellhousing bosses for the mounting through holes. I had to dremel off a little material for clearance.

[cjmurph]

Andrew- That's exactly what I was looking for. I appreciate it. Someday when the planets align I'll find the money for one of the workshop manuals.

Doug- This is one of those 70-71 jobs that's as pricey as it gets isn't it. Previous to reading many posts, I told myself I would re-use the bolts and pocket $90. That was previous, I'm cheap but not naive.
I didn't buy the kit mostly because early diagnosis was simply a destroyed t/o bearing. The dig displayed a worn clutch disk but a very worn flywheel. Clutch disk was likely replaced on an already worn flywheel so I'm probably cleaning up a previous poor clutch job. Now I'm concerned that I need to double check the flywheel wear. With my crude measurments, it's no less than .381mm or .015" and no more than .508 or .020" wear using what I was referring to as a "step".

When I called Pelican due to my uncertainty I asked about the step on the flywheel surface. They stated "yes, you have to have it resurfaced by somebody who knows to do both levels."
I really do appreciate the input and help, but are you guys 100% that a 911 102 201 1R flywheel doesn't have some step on it?

[cjmurph]

Got some good info from Jason with Pelican. Very helpful. He took a good look at my flywheel and stated that it appears to have worn past the groove that is normally found where I stated there was a step.
I'll attach the pic he sent me. Kind of explains where I was getting confused.
I presently don't have access to a caliber for measurment but if I use the 8.5 mm minimum that Andrew states then I'll have some idea of whether it is even resurfacable.
Thanks again
Curt

[andrew15]

Here are the pics from the manual - it doesn't show a groove, but that's probably a later revision to help clear dust:

Regards,
Andrew M

[cjmurph]

Andrew - Thank you very much.

[cjmurph]

Well I borrowed some digital calipers from work and the wear surface on my flywheel is measuring 8.85 mm. (at #1 position on diagram). That gives me .35 mm to machine off. I think for $400 I'm going to try it.

Thanks again
Curt

[Flat6pac]

$400, I ll sell you a good flywheel that doesnt need cutting for $100+ shipping. Remember every MM you cut is all the less clutch you have to wear.
Bruce

[ddubois]

Here's another view from the manual I found helpful for the release fork spacer/spring issue I was talking about. I hope you're saying $400 for a new flywheel and not machining! I agree 0.35mm is not enough left to work with.

[ddubois]

Originally Posted by Flat6pac

Remember every MM you cut is all the less clutch you have to wear.
Bruce

Huh???

[cjmurph]

My bad. I meant save myself from the $400 purchase. My measurements got me a bit excited.

Bruce - I think what you are suggesting is the clutch adjustment changes with flywheel machining, correct?

Doug - do you think I will have to do any shim at the pivot for the cluth fork? I'm likely to end up with the 8.5 mm minimum. I've read some of the stories of guys ending up with the arm of the clutch fork hitting the housing.

[ddubois]

Originally Posted by cjmurph

Doug - do you think I will have to do any shim at the pivot for the cluth fork? I'm likely to end up with the 8.5 mm minimum. I've read some of the stories of guys ending up with the arm of the clutch fork hitting the housing.

Not only hitting the housing, but also the PP. You have to play with the pivot arm cone spacer (perhaps not even use it and just washers), and the flat spring. The problem is that if you study the cross section I posted, there are so many things that affect the final fore/aft position of the end of the release fork where the cable attaches. Machining down the flywheel and a new clutch disc are obvious ones, but also how worn down is the pivot cup in the fork and/or the pivot bolt (another item that should be replaced with the newer Ti version). I probably mated and re-mated my engine/trans 4 times before I got everything just right after installing a new disc/PP/TOB/pivot bolt/PP and FW bolts and machining the flywheel. Search for this as I found a lot of good info here on this issue. It's easy to burn through a ton of dough with these clutches.

[Flat6pac]

The clutch stack has a minimal amount of play in it. The amount is the difference between a new and worn out clutch. Remove metal and there is less of the clutch you can use before its worn out
Bruce