Cylinder #3 unusual wear mark

[Vlad]

After measuring compression we took a borescope and looked inside of all cylinders. Cylinder #3 has a mark at about 10 o'clock. We are puzzled what could cause it? Compression for the particular cylinder is 74/80 and the engine is nearing 3,000 hours of trouble free time. Take a look at the pictures below.

Looking at the piston. There are some swirls visible on top of the piston and against the most visible one there is a wear mark.





That's where the mark is located. About 10 o'clock if it matters.





Closer look at the wear mark.





What could be the cause? RocketBob are you around?

[arffguy]

Is the mark in picture two the side of the cylinder wall?

I had a piston pin plug failure on my engine but it left two marks like that. The piston pin had dug into the wall of the cylinder because the plug wore completely down. This cylinder only had about 700 hours on it.

If I hadn't bought the cheap borescope that was recommended here on VAF I would never have seen it. The compression test was normal and the engine ran great. My friends warned me not to look

I wish I could post a photo but that skill seems to be forgotten.

[Vlad]

Originally Posted by arffguy

Is the mark in picture two the side of the cylinder wall?

I had a piston pin plug failure on my engine but it left two marks like that. The piston pin had dug into the wall of the cylinder because the plug wore completely down. This cylinder only had about 700 hours on it.

If I hadn't bought the cheap borescope that was recommended here on VAF I would never have seen it. The compression test was normal and the engine ran great. My friends warned me not to look

I wish I could post a photo but that skill seems to be forgotten.

Thanks for the comment Mike. The mark is only on one side of the cylinder wall. Just about 10 - 10:30 which is passed pin indentation. Judging from swirls on top of the piston there is a blow by at that mark.

[Weasel]

Rocketbob left posting a while back.. I liked him.

Let us know what you find on that Vlad. I have a keen interest in high time, well maintained engine practices.

[Robert Anglin]

I guess I could stick my foot in it. It's always hard to tell from a picture.
If this mark was at the 9 or 3 o clock you might suspect a rest pin wearing the wall of the cylinder. If it were at the 12 or 6 o clock you may think it could be a piston skirt wearing on the wall with a high time engine of 3,000 hours. If it is at the 10-2-4-7 o clock locations on the cylinder wall one might suspect a ring brake or blow-by gas jetting would be taking place at those locations. The lines at approx. 1/2 inch to the right of the main mark and about 3/8 inch to the left along with the main marking on the cylinder wall would make me think a ring is stating to fail at that location. Sorry just a thought in the dark of a photo.
Hope this helps, Yours, R.E.A. III #80888

[scsmith]

I kinda suspect a broken ring.

[cajunwings]

Vlad: Its fairly obvious that something is rubbing that shouldn't be. The only way to know for sure is to pull that cylinder and have a look. Further running will likely put more metal in the oil and cause more problems & expense. In consideration of the total time and the remote places you go it's time to consider what is the prudent next step.


Don Broussard A&P, IA, ATP
RV-9 Rebuild in Progress
1957 Piper Pacer

[sblack]

Another great example of why borescoping is a good idea. Always best to find this stuff on the ground!

[BillL]

Hard to say for me. It appears to be smearing not scoring, so likely a softer material - bronze or aluminum? You could get some additional clue from its highest point in the cylinder. Maybe blow by is higher, but the swirls on the piston are likely a heavier oil film on that side. Don't we define blow BY as going to the crankcase ?

3000 hrs - pretty nice! What's your plan now?

[Steve Melton]

is there an accepted practice to simply replace rings if everything else looks OK?