1976 18cc with 1984 140 hp evinrude?

[Bushwacker]

If it's the older cross-flow version, those are simple lightweight motors, but I think they got the old 135's up to 140 hp by moving the rings closer to the top of the piston, which makes for a pretty thin top land. Definitely check the compression before you buy it. Don't think it will tolerate any detonation, so I'd be sure to run premium fuel, decarb it fairly often and don't put too big a prop on it! If it'll rev to at least 5500, you should be ok.

[tjspei]

Thank you for the replies. What should the compression be? I am going to check out the motor this weekend.

Tim

[Bushwacker]

Originally Posted by tjspei

Thank you for the replies. What should the compression be? I am going to check out the motor this weekend.

Tim

I'd say about 115 psi or more if cranked with the throttle wide open, but what's more important is the variation between cylinders. I think my old '75 115 Evinrude generally checked between 115 and 130. The smaller the variation, the smoother the engine will run. Variation should generally not exceed 10%.

[Blue_Heron]

Originally Posted by Bushwacker

Variation should generally not exceed 10%.

Denny is right about the variation between cylinders being the main concern, but I'd be happier with 5% or less. That's not unusual for an engine in good condition. I recently bought 215Robert's '79 Merc 140 Tower of Power and all cylinders checked between 120 and 125.
Dave