mid 70s johnsons

[droptine77]

Over the past two days I have looked at two differant mid 70s 70hp johnson motors. I check out the compression on both and they both averaged around 60 psi. Now this was with the engine barely turning over on one and me spinning the prop to turn the motor over on the other(bad starter). Not sure if it makes a differance or not. What should the compression be? Any help would be appreciated.

 

[iwombat]

Re: mid 70s johnsons

If you got 60psi by barely turning the engine over I'd say that's a good sign. They should be spinning at 300+ rpm and you should look for the cylinders to be within 10% of each other. w/o knowing which engines you're looking at the general rule of thumb is 100psi or better is good. Some engines are fine down to 80 or so. And, the gauges are never very accurate either.

 

[droptine77]

Re: mid 70s johnsons

Thank you for the quick response!