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