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  What should the compression be???

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Author Topic:   What should the compression be???
BOB KEMMLER JR posted 02-10-2003 01:01 PM ET (US)   Profile for BOB KEMMLER JR  
It's a 1980ish 70-75hp 3 cyl John/rude.We ran a quick compression test with a jumpack,and got 120psi on the button on all 3 cylinders,i'm not sure if it was spun fast enough to get a accurate reading,but i felt good knowing all 3 were the same.It supposedly has weisco pistons and boysen reedvalves,will this give it anymore power?I know cars,but zilch about boat motors.
JBCornwell posted 02-10-2003 01:33 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Hi, Bob.

The Boyesen reeds and the Wiseco pistons (if they raised the compression ratio) should have increased your output.

Your compression readings are great. I can't think of a better set of readings.

Good luck.

Red sky at night. . .

whalerron posted 02-10-2003 11:28 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Dang Bob! I don't even have 120psi in my truck! I assume that was a "cold" compression test and if so that is great! Of course we now know there is no question about that motor fitting in the wagon. Those pistons are good solid products. Hopefully that motor will last a long time. Did you pick it up yet?
whalerron posted 02-10-2003 11:36 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Bob, I have the service manual for that motor if you ever need to borrow it. It says that the compression should be checked by cranking the motor until the piston pressurizes the cylinder at least 4 times. Even then, the compression reading is not as important as the differences between cylinders. If any 2 cylinders have more than a 5psi difference, the motor has a problem.

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