NS55B 60 psi on both cylinders

[Chrisam16]

When I first bought my boat i borrowed a friends compression tester just to check out. I had never used one before so im not sure it was done correctly. The engine is low hours especially for an 87 model and runs excelent so far. The exterior and interior paint looks great which leads to my question. I got roughly 65 psi on both cylinders when i tested and that seems very low for a great running motor. Is it possible for it to run good with that psi? I have seen images of the same motor being tested at 170 psi on ebay so im assuming it was much higher at some point or do you think i just did something wrong while testing?

 

[pvanv]

Re: NS55B 60 psi on both cylinders

Gauges vary wildly, so take the pound readings with a grain of salt. To do a valid compression test, the motor must be fully warmed, then stopped, the throttle fully opened, and the motor cranked at least 4-5 revolutions, either by electric starter, or with a good, solid, fast pull of the rope. The big thing is that the compression is very even between cylinders. I would expect compression near 100 psi, but again, your gauge and technoque may vary, so YMMV.