Loss of compression

[keithww]

Can sticking valves cause loss of compression?

[Lebro]

If they are sticking open, then compression would tend towards zero.

 

Bob.

[TomMull]

Only one cylinder or all? Sudden loss or gradual? Have you checked valve adjustment? Sticking valves would not be my first guess.

Tom

[classic225]

Maybe you're engine is running to lean and you " burnt" a valve. This would cause loss of compression for sure.

Yves

[keithww]

At present no 1 cylinder shows 50 psi, no 2 160 psi, no 3 55 psi and no 4 150 psi. Any theories would be appreciated.

[RogerH]

Hi Keith,

you can narrow it down a little.

I assume you did the check in the dry mode. ie you simply turned it over and recorded the value.

 

Do it again but before hand put some oil into the bores.

This will help the rings to seal.

If the values increase then it is the rings

If the pressure does not increase then it would be the valve seats.

 

Remember to have a wide open throttle, 5 complete cycles

 

Roger

[Lebro]

Check valve clearances, if all OK ie more than say 5 thou, then it's probably head off time

 

Bob.

[foster461]

Next step for me would be to squirt some oil into the plug hole for one of the low cylinders, rotate the engine a couple of times and test again. If the reading improves significantly for that cylinder the problem is with the piston/rings. If it doesnt improve with the wet test it is probably valves/head.

 

Stan