Let's talk about warped heads. For the head to seal and the cam to turn
properly the combustion chamber side of the head and the cam tower mounting
pads
must be flat and parallel. When the head warps both sides of the head warps.
If you only reface the combustion chamber side then the cam tower pads are no
longer flat. This leads to a tight cam and cam breakage. Two possible fixes,
line bore the cam towers or mill the back side of the head to make the cam
tower pads parallel with the combustion chamber face. To restore everything
back to normal you would shim the towers the amount removed from that side and
use a dead soft aluminum or copper spacer along with the head gasket. By
examining the cam wipe patterns you should be able to tell how much shim is
needed. Measuring the head thickness or better yet measure the volume of the
combustion chambers will tell you how much spacer you need. Two regular
gaskets can
be done, but, you have very little control over the thickness and the
durability would not be as good. Of course you will find that your combustion
chambers are all different sizes (think about it) and they should really be
cleaned up and made the same size. As the head is thinned the cam is lowered.
Since
there a certain number of chain links between the crank and the cam, the
thinner the head gets the more the cam is retarded in timing. The Z actually
has
multiple cam sprocket mounting holes to allow for this. The chain slack is
removed by the tensioner.
Hope that makes things clearer for you. If I missed something I'll try again.
keith
In a message dated 12/30/2004 8:07:50 P.M. Pacific Standard Time,
neuman@radonc17.ucsf.edu writes:
Hello All,
In my quest to reduce my compression ratio and to return my
crank-to-cam distance back to normal I am liking the idea of a thicker head
gasket to make up the difference. With a thicker head gasket I won't have
to shim the cam towers and worry about the wipe pattern on the followers or
worry about having to align bore the cam journals.
Does anybody have any experience with this? I thought that maybe it
was possible to get thicker copper head gaskets? Mike was telling me he
thought he heard it was possible to take two stock head gaskets and glue
them together somehow but he did not have any first hand experience with it.
Mike also has a metal plate in the shape of a head gasket that he got from
Stan a long while ago. Supposedly this plate can be used with a stock head
gasket to lower your CR and return your valve timing. He was not sure how
to implement this. Has anyone had any experience with doing something like
this? I am of course concerned about sealing the head under boosted
conditions. Any (helpful) thoughts on any of this stuff?
Also, man I am feeling really special here, but I don't understand
why a too thin head messes with the valve timing? If the timing chain is
not overly slack I don't see how the valve timing is disturbed? Anyone
wanna set me straight??
Thanks,
Daniel Neuman
Oakland CA
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