heads fly cut
 

I sent my heads (2,2) out for machine work.
The there was some damage from an exhaust leak at the interface of the head to the cylinder as described on page 61 of the rebuild book.
The heads were fly cut .015 for five of them but only .010 for the sixth one. I need to contact the machinist to find out why he didn't cut them all the same.
When he suggested fly cutting them he mentioned that I would have to add shims to the base of the cylinders to replace the material that was removed.

I trusted that he knew what he was doing because he had experience with 911 engines in the past although the bulk of his work was other engines.

Questions.
1) Where do you get these shims?
2) Is it possible to shim one of the cylinders differently than the others so they will be all the same height?
3) Is .005 going to put the engine out of spec?
4) Will the cam bind on the side with the .010 head?
5) How about piston to valve clearance?

Hello there.

This is silly, what was he thinking of?

He has to redo them to match.

You could but should not shim differently.. you may not even need to with only 15 thou off.. take them back for him to do the job correctly.

David

Shims are generally available in .25, .5 and 1mm sizes, and they can be stacked. Our host and your machine shop should carry these. Since you will be shimming each cylinder back to the same stock deck height, the engine specs, valve cleance and cam bind should not be an issues. Obviously, it would be best if all heads are cut the same.

Good luck,

JP

Wayne,
You want to weigh in here?

hopefully he can take the extra .005 off the one head. careful setup will be needed, as it can't have any runout in the initial setup, or it may not clean all around. i try to limit the flycut to .010 (0.25mm) so you can use a 0.50 shim to compensate for the amount removed.

Yes, he needs to redo them. Somewhere in the book it states that you must have at least 3 cylinders to match for each side. It doesn't sound like he has a firm grasp of how these engines are put together...

You might want to send them to someone else who really knows what they are doing - as JW said, if the setup is not right, you could end up in a worse position...

-Wayne

I need to make a correction.
The one head had was mis-stamped and he corrected it by stamping the 5 over the 0.
I should have looked more closely (read put on my glasses).
That aside where do I get the shims or as davidl posts with .015 off do I need to shim or can I just welcome the small increase in compression?
Valves to pistons clearance a problem?

It looks like Wayne has the .25mm and .5mm sizes:

http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?command=DWsearch&description=901104 191

For the 1mm size, you may need to go to EBS, Competition Engineering, Ollies, etc. Don't assume you just need to add 0.015" (0.381mm) of shim. You have to measure the deck height with the P/C installed. There are a lot of tollerances that stack-up here.

Good luck,

JP

Porsche Technical Specifications Handbook states, as Wayne says, that you should have all 3 heads on one side machined. Doesnt say that they have to be machined the same thou. It also states that you shouldnt stack shims "because of the tolerances and unfavorable setting"