Good Compression?

Gary H NC

Gary H NC

Fleet Admiral
Joined
Dec 1, 2005
Messages
8,972
I had been looking in my service manual and can't find anything as far as normal compression readings.
My left bank of 3 cylinders are all in the 95 to 100 psi,while the right bank is 102 to 105..
Are these average,low or just a wore out engine?
Why is one side higher than the other?

1981 Johnson 175
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Good Compression?

Those readings are fine, Gary.

The reason OMC stopped listing 100psi or better is that guages and technique can make as much as 50psi difference.

What matters is the span. 15psi span is okay.
 
Gary H NC

Gary H NC

Fleet Admiral
Joined
Dec 1, 2005
Messages
8,972
Re: Good Compression?

Thanks JB,Really appreciate it!

Now into testing my ignition system,trying to find a low WOT reason.
Already ruled out the prop pitch and carb linkage..:rolleyes:
 
F

freddyray21

Commander
Joined
Jun 10, 2006
Messages
2,460
Re: Good Compression?

those numbers are fine. A decarb might bring them up a bit though.
 
J

just plain ole Bill

Seaman
Joined
Aug 7, 2007
Messages
55
Re: Good Compression?

The next thing you might want to do is the spark plug test followed by checking the Magneto Capacitance Discharge Coils then you might want to .....(Sorry couldn't resist.) :D
 
D

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Good Compression?

Look at the casting numbers on the heads. Make sure they're a matching set. If, in the last 26 years, someone has replaced one head it may not be the matching one. If not, the static compression could be off. I'd also bet a de-carb might yield some interesting results.

Then you have what the engineers call "the difference in compression from side to side is due to rotational directional forces". Buy that?
 
You must log in or register to reply here.
Top