"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

"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 know he has an issue,
he may not mind doing it himself or getting it done if he likes the boat
and/or motor.

Mike

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 know he has an issue,
he may not mind doing it himself or getting it done if he likes the boat
and/or motor.

Mike

wrote:
How can you tell if the head is discolored when the
most heads are painted black from the factory?


Many are painted black, but not most in my experience, & definately not
on this Johnson.

Rob

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.

Yeah you're right about 2-strokes and compression tests (picky picky,)
however it's a rule of thumb I have followed simply because I want to
be consistent in what I do and it does indeed make a difference in
4-strokes. I didn't think about it when I said it... but I feel it
remains a good "rule of thumb" anyway.

Also with regard to discolored paint on the block; you're right
although one of my engine blocks has slightly discolored (gold) paint
and it's still perfect despite the fact it overheated once for about 1
minute before I shut down. While the paint on the block isn't pretty,
everything inside is (I pulled the heads and inspected thoroughly.)
Discolored paint on the head is a clear warning sign that there MAY be
problems. If I were buying a new engine and saw discolored paint or
anything else that indicated overheating, I would want to pull the
heads before I bought it. What's the cost of a head gasket compared to
a total rebuild? Another thing to look for is melted or disintegrating
insulation on the wires around the head (anywhere on the wiring
harness.)

I agree that old engines can be worthwhile - I have a 1972 Evinrude 85
that runs like new and outperforms my much newer Suzuki DF115. Of
course comparing any 2-stroke to any 4-stroke is a little bit of apples
vs. oranges, but I'll take my old oil-burner over a much heavier
4-stroke any day. I will say I like the quietness and lack of smoke
from the zuki thought.

Jeff


Billgran wrote:
"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