Head gasket and cylinders

[coyote101]

Ok guys I took some compression readings from my 70 horse johnson 2 stroke3 cylinder. Came out 123 for top, 130 for middle, and 135 for bottom. I decided to take the head off to inspect the gasket and cylinders since I had some extra gaskets laying around. Head gasket looked great almost new and cylinders look great as well, no scoring and very smooth aside from some carbon buildup. What could be causing these compression variations? I noticed the spark plug threads are slightly cross threaded but I can still get them tight.

 

[jimmbo]

Worn rings/cylinder/pistons, sticky rings come to mind.

 

[Faztbullet]

What year????

 

[coyote101]

Its a 79 model 70el79r

 

[flyingscott]

Its almost 40 yrs old.

 

[coyote101]

Valuable insight Scott. Thanks. jimmbo yeah I agree with you that it is probably an internal wear issue at this point like you suggested. I think I've done about all I'm willing to do at this point. Ill Just put her back together with the new gaskets and cross my fingers.

 

[Bosunsmate]

Just run her on 50/1 and dont push her much til shes warm and it may even out last new motors

 

[oldboat1]

Resurface the head before replacing it (piece of 400 grit wet/dry sandpaper on a flat surface).

 

[coyote101]

On the head gasket is printed "do not use sealer". Does that mean just fit it on and bolt it down or is there anything I need to put on the gasket?

 

[oldboat1]

Nothing extra -- fit it on and torque to spec (which I can't quote for you offhand). Circular pattern, starting from the center.

You may find that refinishing the mating surface might even the compression a bit.