0-320 building compresion.....

[gregory]

Hi all, I'm looking at buying a -12 w/0-320 150hp. Reading through the engine logs the #2 cyl. has had compression in the mid to low 60's for the last ~100 hours. The last annual in the book this spring the compression went up to 72 from 60 last year. only 3 hours flown since last year. The cyl was new overhauled about 200 hours ago.
My question is.... is this bad?....or is this really bad???
Greg

 

[irishfield]

Love tailgate annuals...

 

[Icarus]

Cylinders regularly go up & down in compression, depending on the gauge, how the rings are positioned, is the engine hot or cold & the Nut behind the gauge. Normally its not a BAD thing, check the screen Try & check the compression your self or watch someone else do it again. #2 cylinder is NOT normally the problem cylinder. #4 & #3 tend to get a bit hotter. Sorry no definitive answer here from me

 

[Steve Pierce]

I would fly the airplane and then check the compression. Is the air going past the rings and you hear it out the crankcase vent, exhaust or carburetor? Borrow a borescope and inspect the valves if it is coming out the exhaust or intake.

 

[gregory]

I haven't had a chance to fly the plane yet. Supposed to tomorrow if the wind slows some. I will see if we can check the compression after a hour or so of flying and see what it looks like. It just seems to me it would raise a flag during the last annual to see the compression jump from 60 to 72 after 3 hours of flying. I can understand a few psi..... but....
All the work is from the same mechanic for the last 5 or 6 years, no one new. Maybe he just needs a new compression checker
Greg

 

[Steve Pierce]

I have checked compressions and had one abnormally low, gone out and run the engine and it came up with the others. Also seen the other way around where it stayed the same. Rings, valves and cracks are the airs only way out.

 

[gregory]

But, this one has been low for the last 100 hours or so... low as from 65 to the 60 range..... then popped up to 72....?? Could it have a ring that has spun or something to make it gain that much after only being flown 3 hours in the last year or so? Like I said, it has about 200 hours on it so its well broke in...
Greg

 

[Steve Pierce]

I have had the rings line up one time in all the compressions test I have ever done. I would fly it and check the compression and see for yourself.