Compression.

N

Neptune

Cadet
Joined
Oct 29, 2002
Messages
15
Does anone have the factory compression numbers for a #15120 '53 15hp fastwin 'rude. A '57 QD-18 Johnson 10hp. and a Johnny 9.5. All bores look good with no scuffing, scratches, gouges, etc. My gauge is new and I get readings of 60-62/3 psi on ALL the cylinders from each motor. Either I have quite a coinincedence wherein each engine has eqaully worn rings/bores; readings that are in the acceptable range for each of the 3 engines; or a faulty test qauge. Any ideas appreciated and, I would really love to know where to find the factory specs. Have Selock & Clymer that are no help on compression ranges.
 
H

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: Compression.

The manufacturers don't specify max. and min. compression. The only thing they say is the compression of all the cylinders should be within +/- 10% of each other.<br />You're right, those are some pretty suspicious looking readings. I think I would maybe try another compression gauge. <br />Compressions usually read over 100 psi though.<br /><br />g'luck & c/6<br /><br />Hooty
 
L

ledgefinder

Ensign
Joined
May 2, 2002
Messages
916
Re: Compression.

I get 75psi from both cylinders of a 1964 9.5hp. The data suggest that the older (earlier than mid 1960s), lower horsepower engines run lower compression. I do know that autos and tractors from that era ran lower compression. Anybody know for sure on this? By the way, I get 135 to 150 from the same gauge on mid-1970s motors, and 120-125 on more modern motors.
 
D

DJ

Guest
Re: Compression.

Neptune,<br /><br />Those are not high comp. engines. They would run on just about anything (fuel).<br /><br />Around 60 is OK, as long as they are close to each other in comp.
 
N

Neptune

Cadet
Joined
Oct 29, 2002
Messages
15
Re: Compression.

Thanks all. I did try my gauge on an air compressor tank and it registered the same as the tank gauge so I think it is accurate. I now must assume that all three engines are within 3 PSI of each other across all cylinders. It is comforting to know that the older engines did operate at lower compression as the thought of tearing down all 3 was not sounding so appealing right now!
 
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