I'm to sell my boat which has a 90HP Johnson V4 on it....
One of the possible buyers took the spark plugs off and tested the
combustion of each of the cylinders... one of them failed badly....
Is it worth fixing these things???I don't want to fix it myself cause I
might not get the money back when I sell it.... when a motor of this age
(about 1985) and has these problems i igt worth fixing??


Thanks

"GC" wrote in message
...
I'm to sell my boat which has a 90HP Johnson V4 on it....
One of the possible buyers took the spark plugs off and tested the
combustion of each of the cylinders... one of them failed badly....
Is it worth fixing these things???I don't want to fix it myself cause I
might not get the money back when I sell it.... when a motor of this age
(about 1985) and has these problems i igt worth fixing??



You have to remove the cylinder head to see how bad the damage is. If the
cylinder is not deeply scored, it can be bored oversize and a new piston
fitted.

Being a 21 year old motor, it probably would not be economically feasible to
repair it, unless you planned on keeping it for a few more years. If it is a
salt water motor, then it is not worth fixing.

Bill Grannis
service manager

I had a look at my engine again today...
I found that the red wire that goes to the little box which goes to the
spark plug, had a bad connection...
So I wonder if this was part of the problem before.... the spark plug wasn't
firing and in turn the cyclinder wasn't firing (sorry for my non-technical
terms hehe)
Anyway I cleaned the grotty spark plug up, and fixed up the wiring
connection and then started the engine again and let it run for about 5
mins......
I then turned it off again and took out the spark plug..... its was looking
a bit better... looked like it had a bit of oil on it like the other spark
plugs..... The cyclinder may be working again now???
Without a compression tester, how can I safely check to see if the cyclinder
is firing??
Can I disconnect the cable going to each of the other spark plugs and just
leave the suspect one in??? What results can I expect from this??

So is it possible that the engine failed the compression test simply because
the spark plug hasn't been firing properly in the past??
Thanks




"GC" wrote in message
...
I'm to sell my boat which has a 90HP Johnson V4 on it....
One of the possible buyers took the spark plugs off and tested the
combustion of each of the cylinders... one of them failed badly....
Is it worth fixing these things???I don't want to fix it myself cause I
might not get the money back when I sell it.... when a motor of this age
(about 1985) and has these problems i igt worth fixing??


Thanks

Chehalis Jeff wrote:
To cut to the chase here, whether a spark plug sparks or not has
nothing to do with compression.

Unless the cylinder walls were washed ...

Rob

I REITERATE that spark has NOTHING to do with compression. Whatever
"unless the cylinder walls were washed" means is beyond me. Spark is
spark and while a weak spark can be quenched by compression, if you
don't have compression in a 2-stroke it's due to a physical problem
that is allowing the air/fuel mixture to escape either into the
crankcase or to the outside air, which could include piston holes,
blown head gaskets, broken rings, badly scored cylinder walls, etc.,
but a lack of compression and whether you have a spark or not are
UNRELATED. You need a proper fuel/lubricant/air mix, compression and
spark (at the right moment) for a 2-stroke engine to run.

In order to improve compression, you need to lessen or eliminate places
where the fuel/air mix can excape. Check the head gasket, inspect the
top of the piston and look carefully at the cylinder walls; it should
be fairly obvious what the problem is.

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. The compression should be within approx 10lbs of each
other or less. Closer is better. For example, if you have an older 4
cyl OMC outboard like I do, you might find something like this:

Cyl 1: 100lbs
Cyl 2: 97lbs
Cyl 3: 101lbs
Cyl 4: 99lbs

This would be acceptable.

However something like this would show a problem:

Cyl 1: 100lbs
Cyl 2: 97lbs
Cyl 3: 101lbs
Cyl 4: 79lbs

If you've run the test several times and this is what you see, the
engine may run (sorta) but Cyl 4 has a serious problem. Remember,
always do compression tests with the throttle wide open.

Compression testers are cheap and anyone who has an engine in their
garage (lawnmower, outboard, inboard or automobile) should have one.



trainfan1 wrote:
Chehalis Jeff wrote:
To cut to the chase here, whether a spark plug sparks or not has
nothing to do with compression.

Unless the cylinder walls were washed ...

Rob

"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

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