2,7 heads sealing surface machined
 

Most of my heads have machined surfaces to seal to the cam towers. Porsche workshop manual says no machining.

My question is is this a deal breaker on these heads. I know I should replace but you know the expense. Other than flat edge them, is there a set of measurements I could take to effectively decide if they are junk?

Getting ready to send to shop or replace. I can post pictures tomorrow if you would like to see what I am talking about.

john

I hope that's not true because I had a set in my race motor for the past 4 years. You can measure them, stock height from the cam carrier surface to the head surface is 84.5mm

You are right, my statment last night from memory was not true. It is the cylinder side that is machined, and it looks like it is angled.

John

I don't see why you can't machine the surfaces....for the amount you take off...you just place a thicker shim at the cylinder base to make up the difference...so the compression ratio and piston clearance remain the same.
Or...am I wrong?
Bob

Well, the cylinder seals in the cut out right? And I would guess you are right about maybe taking a turn there to flatten things out, but mine are liked decked over the top surface. I am not sure why you would do that, as it is not a sealing surface?

I took some pictures, now I have to find my download cable.

John


http://forums.pelicanparts.com/uploa...1402169055.jpg


http://forums.pelicanparts.com/uploa...1402169145.jpg

Those surfaces don't look cut and even in the picture the seats look badly pitted might want to just look for a good set of core heads.

Review what John Edwards has to say at Costa Mesa R&D in Costa Mesa, CA

https://www.youtube.com/watch?v=dncyBPHCKyQ

Hope this helps,
Thor

Thanks that video is helpful,

Obviously replacing is not what I want to hear, so I have not finished cleaning them up. The seats are not as bad as they photographed.

I will clean them up and post more pictures and then you guys can give me your opinions again.

Thanks

The heads are usually resurfaced when you rebuild an engine. Those heads look like they could use a resurfacing. They look normal, all of them have a stepped surface like that. Most shops take .010 inches off to clean them up. All it does is raise your compression slightly.

-Andy

I measured the step on one and It is 2.1 mm. That equates to .082"

The say 911 deck height is usually .03 to .04 inches.

Is that step my deck height?

No, when the surface is machined that outer step also gets machined otherwise it can interfere with the cylinder fins.

Deck height is the distance from the top of the piston to the top of the cylinder. It doesn't have anything to do with the heads.

The sealing surface can be damaged and machine back true. It affects your head volume and thus your compression.

I had my heads rebuilt and they have the "step":
http://forums.pelicanparts.com/uploa...1390572129.jpg

What is the depth of that step?

Here they are cleaned up a bit.


http://forums.pelicanparts.com/uploa...1402286108.jpg


The two samples I took got 2.01 MM to 2.55 mm

http://forums.pelicanparts.com/uploa...1402286168.jpg


http://forums.pelicanparts.com/uploa...1402286200.jpg

The seats cleaned up well.

I don't see the need to replace, just have freshened. Do you all agree?

"The two samples I took got 2.01 MM to 2.55 mm" Herein lies one issue.

I think it may be easier if you got your hands on Anderson and Woods 911 Engine Rebuilding Course booklet that explains in great detain how the case, cylinders and heads go together. It also includes what measurements are key and how to go about doing them. There are some other things you need to measure like head volume and the deck height you mentioned. Variations in your heads like the one quoted above will absolutely affect how you put the engine back together again.

I think you are asking a question no one here would be willing to answer for you. I'm sure there a few machinist qualified to do so on this board but none would venture to answer your question based on a few pics and one measurement. If you're not sure, you need to get a professional involved in assessing the heads.

Sorry for the confusion.

My base question is if the heads can be worked with, not if the work is necessary. I expect that I will have to have the work done. What I am trying to do is establish the viabilty of these heads as cores.

Thanks
John