Andy,
I always love a puzzle, so I'll give this one a try; although if I'm right
your friend may not be all that grateful after all. I hate to be the
pessimist, but it seems to me that the low compression on one cylinder is
probably the sign of something serious that won't get better with time.
From your description, I suspect that the "miss" your friend is
xperiencing is more than what would happen if, for example, he just pulled
the spark plug wire on one good cylinder. If this is so, then maybe the bad
cylinder is blowing back into the intake manifold, which can screw things
up pretty bad for the rest of the cylinders. How could this happen? A lob
going flat on a cam would do it. For example, if the exhaust valve wasn't
opening on a particular cylinder, then the exhaust gases would blow back
into the intake manifold when the intake opened. Other variations on this
theme can also be imagined. For example, a broken valve spring or just very
badly adjusted valve lash. I would suggest taking the valve cover off and
observe the movement of the rocker arms as you crank the engine over. I
hope this isn't too difficult on a Healey. But before you do this, you
probably ought to start by carefully observing how the engine runs at idle.
Do all cylinders fire equally well? Pull the plug wires one at a time an
note the difference, if any, in rpm. If everything is OK, the engine should
idle smoothly and there should be the same drop in rpm when each plug wire
is pulled. Also, note how much blow-by there is, which could be a clue as
to a broken ring, or just poorly seated rings. I suspect you will find some
problems associated with the cylinder with the low compression. But pulling
plug wires is easy to do and you may as well start there before pulling the
valve cover. Hey, at least there's only one. ;-)
Good luck,
Bob
Robert L. Palmer
UCSD, Dept. of AMES
619-822-1037 (o)
760-599-9927 (h)
rpalmer@ucsd.edu
rpalmer@cts.com
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