"Vic Smith" wrote in message
...
On Wed, 23 Jul 2008 08:28:39 -0700, JR North
wrote:

As you will recall, In our last episode, I was preparing to install the
new starter in my Merc. 5.0. I did a compression test with the old
starter in place, 150 all around. After sitting 2 weeks, the new starter
is in; I cranked it with the plugs out (no manifolds installed yet) And
it spun 3 revolutions with a *Clack* every 360?. I thought in this brief
time that possibly a tooth was sheared on the flywheel ring, but after 3
revolutions the engine locked and would not turn. ****. I was thinking
maybe a socket I had holding the Qjet choke open had somehow fallen into
the intake manifold and wedged an intake valve open. Ok. I put a chain
wrench on the balancer and found I could rotate the engine backwards,
but would lock at the same point forwards. I pulled the valve covers,
expecting to find an offending intake valve hung open, with slop in the
rocker arm as a result. Found it, alright, but an exhaust valve, not
intake. Feeling up the #4 exhaust port with my finger, I can feel the
broken end of the exhaust valve stem. The valve head is loose in the
combustion chamber, preventing the piston from reaching TDC. DOUBLE
****. In the 2 weeks since the compression test, the #4 exhaust valve
seized in the guide, and on cranking, because the valve is at an angle
with the piston, was broken off. Now I get to pull the heads......
Oh well, the engine is 18 years old, has 495 Hrs on it, and with all
that down time, a seized valve is not unusual.
JR

That's weird, since you were cranking it 2 weeks ago.
What do you suppose caused it to seize?
I've never heard of that happening on a 305, but you say that's
not unusual.
I'd like to hear the autopsy report after the stem is driven from the
guide.
This boating stuff is starting to scare me.

--Vic

Salt water in the valve guides.
Rebuilders won't touch heads from sal****er boats.