Hello Mike,
When compression tests produce large variations in pressure from
cylinder to cylinder, the rings are usually credited with the
problem. However, the service manuals for my Jaguars state that
one should suspect poor sealing valves first. If accompanied by
burning oil, rings are again an obvious target but do not forget
the valve guide-to-valve clearance. If this spacing is excessive,
oil can blow by the inlet valves assisted by the pressure
depression of the inlet manifold. This problem is epidemic in
Jaguars to the point that later engines have integrated a valve
stem seal at the top of the valve guide.
Adding oil to the cylinder before a second pressure test can
identify ring problems frequently but can also wet the surfaces
of the valves and their seats providing a questionable
interpretation of rings condition. The aformentioned Jag manuals
also specify that the pressure tests be made with 1) all plugs
removed, 2) carb buterflies fully open, 3) engine spinning on the
starter. Obviously, removing the low tension lines from the coil
is a good idea.
Let me know how it goes. I just went thru this kind of discomfort.
Fortunately, my engine problems were entirely in the head - the
Jaguar's head, not mine (this time).
Good luck,
Rick
cc british-cars
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Richard O. Lindsay / / / / / / / / / __
Senior Research Scientist / / /-/ /_ -/ /-/ /_
Amoco Production Research / /_/ / / /_/ __/ o /_/ __/
/
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