Pressure differential on Johnson

[feargalb123]

Hi,
I have very low power on my 1978 Johnson V4 85hp engine. I done a pressure differential check and got between 6 and 6.5 bar on 3 cylinders and only 2 on the 4th. I put some oil into the cylinder and this came up to 2.5 bar. Seems like piston rings is the problem, but is there any other possibilities. Has been suggested that it could be a head gasket which I seriously doubt or a valve. Any suggestions?

 

[tashasdaddy]

Re: Pressure differential on Johnson

yes it very well could be the head gasket. at any point your down to pulling the head anyway to see what the problem is. so there will be no loss, by pulling the head, for inspection. could be an easy fix. the ideal is over 100 psi, and equal with in 10%.

 

[kenmyfam]

Re: Pressure differential on Johnson

I think you will have trouble finding a valve issue on a 2 stroke motor for a compression problem. Could well be the head as TD says and it is the starting point of a teardown. Could be as simple as a blown head gasket.