1988 10HP Envinrude - Compression

[Calibra]

Hi

​Friend of mine has just purchased a new engine.

​Johnson 10HP 2-Stroke 1988

​Engine won't fire up properly and runs a bit rough when accelerating.

Compression shows

​Cylinder 1: 90 PSI
​Cylinder 2: 70 PSI

The compression is low as I'd expect 100PSI or more, and there is nearly 20 PSI difference between the two

We have a new head gasket to fit, but we don't have a manual to follow.

​Does anyone know what order the bolts do up and to what spec?

Thanks

​James

 

[flyingscott]

18-20 ft/lbs do it in 3 steps and start from the center and work your way out. The piston with 90 psi is fine I would be concerned about the 70 psi. Those are not high compression motors.

 

[racerone]

The manual for one of your other motors is essentially the same.-------Pull the head off and have a look.------Reason for low compression might be obvious.

 

[raczekp1]

i think you should buy new oversize pistons kit and rebore cylinders.
new head gasket will not help.
on ebay there is seller who has piston kits in good price.i rebuild few 9.9 on those pistons

 

[Crosbyman]

that parts list place doe not show a10hp in 1988 is it a 9.9

 

[racerone]

There was a GT 10 marketed at one time.--Not sure of the years.

 

[Calibra]

Thanks for the replies.
​Indeed, it is a 9.9HP. Does this mean a 15HP carb won't fit it?

​Anyway... My mate replaced the head gasket and is now getting 115PSI compression on both Cylinders