Anyone who's had a low compression cylinder?

[GNICETRY]

Which one was it? My #6 cylinder is about 50 lower than the rest.

 

[325DR]

Mine was 20# lower in #5 if I remember correctly.

 

[turboman38]

From my highest to lowest I had a difference of 22. I was throwing a fit at that time but I've been told not to worry about it. 50 sounds too high to me. Sorry to give you bad news but it sounds like you have a bad or broken ring. Squirt a couple drops of oil in the cylinder and then check it again. If it goes up more than say 7 points then do a leak down test to see if it's the rings. I did the oil trick and mine went up 6 points. I'm still worried but my motor is fresh so I'm not tearing it apart until it breaks.

 

[Iceman]

Mine was #3.When I pulled it down it had a burnt piston and valves.

 

[GNICETRY]

If I squirt oil into the cylinder and it increases, what does that mean? What would leak down test tell me that a compression test wouldn't?

 

[325DR]

Originally posted by GNICETRY
If I squirt oil into the cylinder and it increases, what does that mean? What would leak down test tell me that a compression test wouldn't?

A leak down test would allow you to figure out if it is
1.) a leaky piston ring (you will hear air in the crankcase
2.) a leaky intake valve (you will hear air in the intake manifold)
OR
3.) a leaky exhuast valve (you will hear air in the exhuast)

A compression test will just show you a number (the compression) but doesn allow you to find the leak.

 

[machinegun]

If you take a reading and then squirt oil into the cylinder only a little and the compression increases then you would probably have ring issue. This could then be substantiated with a leak down test.