IO-540 Wonky Compression

Since new, my Lycoming IO-540 has erratic compression on the #3 cylinder. Finally, on the advice of the engne builder, on the second annual, I pulled the cylinder.

There was no obvious visual problems with the cylinder, valves or rings. What I did discover, however, was a missing wrist pin end cap. There is no sign of it in the crankcase and no metal in the filter or drained oil.

There is a strong indication that it was never there since new.

My question for the engine experts: could the missing end cap be related to the erratic compression (from 55 to 70/80)?

The cylinder and piston are at the engine builder now for warranty rework, so things are getting fixed.

Cheers,

vlittle said:

There is a strong indication that it was never there since new.
Cheers,

Click to expand...

Wow. Not good.


I just had to pull a jug 2 weeks ago due to intake valve guide wear that caused the valve to not seat properly 750 hr since new. I thought these things should easy go past that without problem when flown at the rate I do. BTW this was an ECI cyl new in 2012.

Vern, if it had ever been there I'm sure the piston would be trashed long before the plug "disappeared". Without the plug the steel pin would do a number on the cylinder walls quickly if it contacted. That could be your compression problem source.

aerhed said:

Vern, if it had ever been there I'm sure the piston would be trashed long before the plug "disappeared". Without the plug the steel pin would do a number on the cylinder walls quickly if it contacted. That could be your compression problem source.

Click to expand...

No obvious sign of damage, but it doesn't take much. Cylinder only has 68 hours on it! Leakage is past the rings, which is consistent with cylinder bore damage. We'll see. I think it's also possible for the piston to rock slightly if the pin is not centered.

EDIT: I looked at the photo of the exposed end of the wrist pin and it shows some erosion/scuffing around the outer circumference of the pin... this may be the root cause. I'll post the findings from the engine shop.