LD wrote:

First, I hope you were correct in your original test resulting in "zero"comp
in one cyl. If you don't see anything unusual, looking at the top of the
"bad" cyl, compared to the others, look closely at the valves at the seat
area. You could have some burned pitted area there. You will need a valve
spring compressor which you can buy for $20-30 bucks at the local ap store
or possibly rent. When you "blew comp. air in spark plug hole", did you
seal the air source (with a rubber or threaded fitting to the hole where you
had a "sealed" system and heard no air leaking, at 100-150psi? Or, did you
just blow air into the hole and hold your hand over the exhaust/intake?

I hate to say it but if you can't see anything "unusual" with the
valve/seat, or the gasket or the top of the piston, or, some marking/scoring
on the cyl wall w/piston at bottom, you may have mis-read the gauge or not
seated it properly on that cyl. I think a week spring/sticking valve was
already covered and you need to remove it to check (along with the seat). I
would say there's one other possibility but it would have to affect all
cylinders. That is a slipped chain on the camshaft, which would change the
valve timing, possibly resulting in the two conditions you
mentioned--backfiring and zero compression--but would affect all cylinders
equally.
LD

"t" wrote in message
.. .
mercruiser (chevery) 350. Compressions test showed 1 cylinder had 0. All
others were ok. Engine backfires and sputters. Doesn't seem to be
leaking
much oil if any at all.

here's what I tried:

--
Pulled the valve cover. Valve is moving up and down.
cranked the motor until the valves were closed, blew compressed air in
spark
plug hole, no air came out the exhaust or intake.
yanked the head off, no hole in cylinder (that I can see), head gasket
look
ok from what I could tell

Any suggestions?



Take the plug out stand a rod in the plug hole if it moves up and down
then you should know what your problem is.