Compression test standards

Is there a compression test rating list for the various motors.?

I couldn't find anything in my repair manual.

Joe.

Re: Compression test standards

The actual numbers aren't super important unless they are SUPER low. They should just be within about 10% of each other.

Re: Compression test standards

Depends on the outboard in question. For the earlier big twins, 90 psi is OK...nothing to worry about. For some of the smaller outboards, even 60psi will do OK. For later model engines, compression numbers are higher.

What's most important is the the cylinders be with 10% of each other or so.

Re: Compression test standards

thanks guys I was a bit worried as the psi on my "new" 1977, 140 Evinrude read 95-97,while someone elses same motor read 120psi.

One would think that since compression is so important in these motors every manufacture would specify psi standards for every motor they make.

Joe.

Re: Compression test standards

Ah, but every gauge is different.

Re: Compression test standards

clean up your innards, bet the compression comes up. here's how.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

Re: Compression test standards

If you have stock heads (321900/322215) on your 77 140, the compression (when new) would have been 130+. It depends on what heads are still on your engine. If the heads were ever replaced when overhauled, they could be lower compression bathtub heads and would give you the numbers you stated.