wrote in message
oups.com...
How can you tell if the head is discolored when the
most heads are painted black from the factory?

MikeT wrote:
"Billgran" wrote in message
. ..

"Chehalis Jeff" wrote in message
oups.com...

Remember,
always do compression tests with the throttle wide open.



Just for kicks, take a compression test on a two-stroke motor with the
throttle closed, throttle open, and your hand over the carb blocking
off
all air flow. You will find that the compression numbers are all very
close. Why you ask? Because the exhaust port is open to ambient air
until
the piston ring closes it off. On a two stroke, the compression only
builds when the exhaust port is closed off by the top ring. Try it, if
you
don't believe.

Bill Grannis
service manager

Joe is right, compression is compression, ignition, and spark plugs are a
different issue.

If the engine does not show signs of discolored paint on the heads from
overheating, AND you want to mess with it, a 21 year old OB is not old if
taken care of, if it is corroded, filthy, signs of oil/gas leakage, bad
seals in lower, shifts funny, then let it go as parts. I have a 1985 Merc
4
cyl that is like brand new, compression 140 to 145 across all 4, you
could
eat off the heads. Same as my 1989 15 HP Mariner. But I seen other OB's
only
5 years old in 10 times more used condition than mine, from neglect, and
not
having maintaining them. Watch out for discolored heads on any outboards!

If you are selling with a bad cyl, then let the buyer knowe black, he
has an issue,
he may not mind doing it himself or getting it done if he likes the boat
and/or motor.

Mike


He is right, my heads are black paint, but my black paint is shiny and no
flaking, black shows overheating by dulling of paint and it will turn
gold/lighter as well.

Chehalis Jeff wrote:

Before I tore down my engine, I would carefully redo the compression
test, and then do it again... The individual who 'tested' it may have
been looking for a lower price and fudged on the results. Just a
possibility.

That was my thought, too.

My other thought was that someone who was working on the ignition
wiring as first aid to a compression situation might be well-served by
saving the cost of a compression tester and instead paying a trusted,
experienced mechanic to perform the test.

But then I just re-read the original post:

"One of the possible buyers took the spark plugs off and tested the
combustion of each of the cylinders... one of them failed badly.... "

That's combustion, not compression. Like (apparently) everybody else, I
thought the buyer did a compression test and found a bad cylinder. In
the best case scenario this could be gummed rings; the worst cases have
already been mentioned.

So maybe the buyer did a simple "spark test" on each cylinder and
simply found a plug that was oil-fouled and wasn't firing? The owner
may have already fixed that by securing "the red wire that goes to the
little box which goes to the spark plug." There's reason to be
optimistic here.

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