No Compression in One Cylinder

[Miroash]

I have a 1982 90hp Johnson that has 100-110psi in all cylinders but one which is about 20psi. what can cause this, will it be an easy fix or will it need the cylinder to be redone. I know there is no certain answer until I get it apart, but I was wondering if there is a common problem with these motors.

 

[wilde1j]

Re: No Compression in One Cylinder

Could be a blown head gasket. In any case, pull the head and have a look. If the low cylinder shows a damaged bore, piston damage, etc., a rebuild is in order. Inspect the head and gasket very carefully. May be just a new gasket needed.

 

[tashasdaddy]

Re: No Compression in One Cylinder

no idea until you pull the cylinder head. look at the piston, rings, and walls.

 

[Miroash]

Re: No Compression in One Cylinder

Could be a blown head gasket. In any case, pull the head and have a look. If the low cylinder shows a damaged bore, piston damage, etc., a rebuild is in order. Inspect the head and gasket very carefully. May be just a new gasket needed.

I assume it's not likely it will be the head gasket that is the problem though, huh. If I get it apart and I do not see anything wrong with the gasket or the cylinder wall, does that mean the rings are bad?

 

[tashasdaddy]

Re: No Compression in One Cylinder

then you pull the exhaust plate. to see the side of the pistons.

 

[wilde1j]

Re: No Compression in One Cylinder

Get it apart first and post some pictures.

 

[Miroash]

Re: No Compression in One Cylinder

ok, will start pulling it apart tonight, this was a saltwater motor and bolts are pretty rusted, is this motor be worth the trouble to repair? I only paid $300 for it, other than this one cylinder it seems to run great.

 

[Miroash]

Re: No Compression in One Cylinder (Any and all opinions welcome!)

Re: No Compression in One Cylinder (Any and all opinions welcome!)

I heard that if the rings are "Stuck" (whatever that means) I can try "Decarbing" (whatever that is) in an effort to loosen the rings and I could regain compression in the bad cylinder. Have any of you ever heard of this working and what does it involve doing, is it something I can do.

 

[iwombat]

Re: No Compression in One Cylinder

It's something to suspect if your compression is more in the 60psi range. With 20psi it's really unlikely that it's just stuck rings. Possible though. There's a decarb procedure in the FAQ section.

 

[Miroash]

Re: No Compression in One Cylinder

It's something to suspect if your compression is more in the 60psi range. With 20psi it's really unlikely that it's just stuck rings. Possible though. There's a decarb procedure in the FAQ section.

Ok, thanks. I read the Decarbing procedure in the "Top Secret" thread. I think I will try that first before I do a tear down, maybe I'll get lucky but I'm not gonna hold my breath.