Subject: [Fot] Odd compression?

From: Edward Dunn <[email-masked]>
Date: Mon, 20 Aug 2012 01:29:28 -0700

My '71 GT6 race car continues to vex...

After having the engine blow, and then be rebuilt, it broke a rocker arm at
Willow Springs in practice. Bent the #1 valve a bit too.  Took the head off
and had a pretty reputable cylinder head rebuilder go through it. He found
that the engine builder had not installed the set screw that keeps the rocker
shaft in line with the oil feed hole in the upright. Hence, under-lubrication
to the forward end of the rocker shaft. He replaced one valve, all the
rockers, and the rocker shaft which was scored. Surfaced the head too.  We
installed the head last week, Torqued gradually in sequence @ 15 lb ft, then
25, then 45.  Adjusted the valves, and decided to do a compression rest just
for fun. (used a Payen head gasket)

What we found was interesting, but not good: #1 cylinder @ 170; #2 @ 120;
#4,4,5 @ 140; #6 @ 170 psi. this on a rebuilt engine with two hours run time
before failure...  The compression test was done without the intake on the
car, so it hasn't run yet. The cylinder head guru said to run it, and then
recheck. We'll also do a leakdown test then.

Any speculation? First thing that comes to mind is a not flat head or block,
of course. Then rings?

Ed
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