1978 115hp jonhson copression help

[bowman103]

testing cyl, right now have just picked up tester i dont now what the compression should test on this motor model is a 115ETL78C lost all power on lower right cylinder also would it be possible to change rings or just one piston if bad thank you

 

[boobie]

Re: 1978 115hp jonhson copression help

What's the compression on all four cylinders with the plugs out ??

 

[bowman103]

Re: 1978 115hp jonhson copression help

What's the compression on all four cylinders with the plugs out ??

got 94 psi on top 2 bottom left and zero on bottom right standing at back of motor thanks

 

[emdsapmgr]

Re: 1978 115hp jonhson copression help

125 lbs would be normal for a factory-fresh engine. I'd pull the right head and see if the head gasket is blown on the bottom right cyl. It is permissible to replace just one piston. Once apart, you might as well put in 4 new ringsets. No point in having one of the other old ringsets go bad 6 months after you just had it apart.

 

[bowman103]

Re: 1978 115hp jonhson copression help

125 lbs would be normal for a factory-fresh engine. I'd pull the right head and see if the head gasket is blown on the bottom right cyl. It is permissible to replace just one piston. Once apart, you might as well put in 4 new ringsets. No point in having one of the other old ringsets go bad 6 months after you just had it apart.

thanks for quick reply will pull head of tomorrow after work what would be most noticeable on head gasket to look for if it was blown thanks i will replace ringsets on that side never thought to do that thank you

 

[emdsapmgr]

Re: 1978 115hp jonhson copression help

There is a stainless seal ring around each cylinder on the head gasket. If that seal ring is intact, that cylinder should make compression. If the seal ring is damaged or not continuous, that cylinder won't hold compression. You will immediately see any defect in that ring if there is one.