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What Should the Compression be?

G

Greg D

New member
I have just gotton a 1969 9.5 h.p. Evinrude Model 9922 S. Does anyone know what the factory compression was for this model? So far I can't find it in any manuals or books. A test was just done on the engine while it was cold and after having been unused for at least a year. The #1 Cyl. was 70 lbs. and #2 Cyl was 60 lbs. Quite low in my book. We did not run the engine to warm it up before the test or do a second test after injecting some oil in the cyl. Don't know if it's worth putting much money into this engine. Comments and help would be welcome.
 
They don't list compression specs, to many variables.
I usually consider anywhere from 70-90 lbs good on those with a manual starter. With the compression numbers you have it should start and run if the spark and fuel are good. When you get it running do a decarb and you might pick up a couple of pounds of compression.
 
Thanks for the quick reply! I'm not sure what you mean by a decarb. Would that be a carb cleaning and rebuild? The tech I was with did put a very small amount of fuel directly into the carb after checking that we had a spark and it did start to run for just a moment. It was not in a tank and not connected to a fuel source so we were not trying to run it. I just wanted to know if it basicly would run. I would plan on replacing the impeller, cleaning and rebuilding the carb, changing the gear oil, and then firing it up to evaluate it. At that time I'll run the compression test again and see if it improves. At what reading should I be worried about the compression, and what is the acceptale difference between cylinders? Do you think I should also replace the thermostat as well at this time? The engine was a salt water engine and I wonder if I have to worry about scale buildup in the cooling system. Any ideas?
 
Decarb is running something like seafoam through the system to remove carbon around the rings and in the combustion chamber. I have seen those engines start ansd run with compression down in the 50's compression area, did not idle well, but it ran. The compression should be within 10% of each other, but if the engine has been sitting for awhile, the readings will probably improve after you run it for awhile. Pull the thermostat and have a look at it, you can test it to see if it is operating properly. I would get the engine running properly and see how the cooling system is working.
 
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