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Date:         Wed, 5 May 1999 16:24:45 -0700
Reply-To:     Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Subject:      Arrgh!! Do I use the cylinder head shim, or not??
Comments: To: type2@type2.com
Content-Type: TEXT/PLAIN; charset=US-ASCII

Hey all,

Haven't made much progress in my two '81 Vanagon engine rebuilds as I've been mulling/stewing/freting over problems with my two sets of rebuilt heads.

Here's the general question: how critical is it to maintain the "original", "factory" distance between the top of the head (the point where the rocker arm pedestals touch the top of the head) and the face of the crankcase?

To put this question in a more tangible form: do I use the head spacer with the rebuilt AMC (Spanish) heads, or not?

And here's the background and my understanding of the situation:

When I bought these AMC heads new, many years ago, the instructions that came with the heads said that the sealing ring or shim that goes between the head and cylinder should not be used. I questioned the list about this (i.e., why the shim isn't necessary) and the response I got was "because the shim is cast in place in the head." Accordingly, NOT using the shim didn't mess up the head geometry established by the factory (and didn't mess up the compression ratios.)

Fast forward to today, when I get these heads rebuilt. Knowing a little bit more today than I knew back when I bought these heads new (though, it seems, I still don't know enough) I decided to cc the heads and got less-than-perfect results; a "small" measurement of 52cc's and a "large" measurement (on the other head) of 57cc's. Cranking these numbers through the spreadsheet I get a range of compression ratios of from 7.53 to 7.15 using the head shims, and from 8.04 to 7.60 without the shim. The last range is clearly too high, so I've got to use the shims, it seems.

In talking to the shop that did the heads, they've advised that I can use "non-standard" barrel shims to bring the compression ratios closer from one side of the engine to the other, but there's been no talk about shimming the rocker arm pedestals or changing the length of the push rods to compensate.

To add to my confusion, I found the VW tech bulletin that advised using a 1.6mm (.063") barrel shim and no head gasket in place of the original paper barrel gasket and head shim. "Ahhaa" I shouted, the correct "stack up" is .063". But, when I measure the barrel shim and head gasket that came with the gasket kits, I get a combined measurement closer to .04".

I guess I need to go back to the shop with these heads, corner the mechanic and have a long talk about all this........

But, am I running myself around in circles for nothing? Does the fact that these engines have hydraulics somehow render all this worrying moot?

--------------------------------------------------------------------- Tom Young young@sherlock.SIMS.Berkeley.EDU Lafayette, CA 94549 '81 Vanagon ---------------------------------------------------------------------


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