1961 40HP Evinrude - what should compression be at?

[newtoengines]

1961 40HP Evinrude - what should compression be at?

 

[JB]

Re: 1961 40HP Evinrude - what should compression be at?

Compression should be both cylinders within 10% . As long as it is above about 60psi, PSI is irrelevant because there are too many variables.

 

[newtoengines]

Re: 1961 40HP Evinrude - what should compression be at?

we were reading about 55PSI for both cylinders but we made a mistake the compression tester was longer than the spark plugs so the pistons knocked the tester and 1 cylinder got bad threads from it so we are going to retap that tomorrow with an insert, we both learned something, i think if the pistons had a chance to do a full stroke instead of hitting the tester they would have been stronger than 55

 

[kenmyfam]

Re: 1961 40HP Evinrude - what should compression be at?

we were reading about 55PSI for both cylinders but we made a mistake the compression tester was longer than the spark plugs so the pistons knocked the tester and 1 cylinder got bad threads from it so we are going to retap that tomorrow with an insert, we both learned something, i think if the pistons had a chance to do a full stroke instead of hitting the tester they would have been stronger than 55

Yep, checking the thread length on the tester to the spark plugs is a must. Hope that is the only damage it caused.