Scoring on cylinder wall found during annual

[Guillaume]

Hello everyone,

 

During my borescope inspection, I found a light scoring on the cylinder #3 wall (you can find the video below)

 

Engine is a Lycoming IO360 A3B6D

TT 2794h

TSO : 887h (overhaul in 08/2002).

Hot differential compression on cylinder #3 is 78/80.

Oil filter inspection revealed a very small amount of metal flakes. Some flakes are magnetic.

As of today, the engine runs fine and performs as expected. 

 

In the video, the piston is on the bottom of the frame.

 

 

 

What is your technical opinion on this matter ?

 

Thanks.

 

Edited December 20 by Guillaume

[ArtVandelay]

Only about 40hr/year, has this engine ever been idle for long periods of time?

[N201MKTurbo]

I wouldn't worry about it.

[Pinecone]

Monitor to see if it gets worse or stays the same.

[EricJ]

Cylinder walls are the toughest thing for me to assess with a borescope because of reflections, etc.   That doesn't look to me to be anything alarming, but I'd continue to check it on subsequent borescope inspections.  It's the sort of thing that sometimes disappears from one inspection to the next.   Compression is good, so there's nothing awful going on.

Ferrous flakes can be from quite a few places and it's not abnormal to have a few in the filter.  That should be monitored as well, though, as always.

 

[Guillaume]

22 hours ago, ArtVandelay said:

Only about 40hr/year, has this engine ever been idle for long periods of time?

Not really. Being based at a grass airfield, I can't always fly due to runway surface condition in the winter.

During this period, the engine is being regularly ground run.

I'm using straight ashless dispersant oil + camguard for best corrosion prevention.

Thank you all for your advice.

An engine shop also confirmed your assessment : Keep running and monitor.

 

Edited December 21 by Guillaume

[Alan Fox]

It is very subjective , and almost impossible to assess , they all look bad at times.. it has compression , doesnt burn too much oil , and trace metal in the filter...  Leave it alone and fly it... check it in 20 hours ... I wouldnt even think twice about signing it off at annual..

[M20F]

Scoring is caused primarily by three things.  Piston gets very hot and expands (or barrel is cold and you whack in the power).  Lack of lubrication.  Dirty or leaky injectors.  
 
I would check your injector, if it is the issue very easy and cheap to fix. 

Monitoring CHT & Oil temps in all phases of operation is a given. 
 
The sad cause of cylinder scoring in a Lycoming is the lifters or cam going bad.  You can measure valve lift easy enough to check the cam.  For the lifters you have to pull a cylinder though I have heard there is a way to do it through the dipstick though I have never done it. 
 

[Pinecone]

5 hours ago, Guillaume said:

During this period, the engine is being regularly ground run.

In general, ground runs are not a good idea.  You need to get the oil to full operating temperature for a hour.

[PT20J]

Lycoming told me that the most common cause of scoring was high rpm (>1200) immediately after a cold start. They also said not to worry about any scratches that weren’t deeper than the cross hatch. 

[ArtVandelay]

Lycoming told me that the most common cause of scoring was high rpm (>1200) immediately after a cold start. They also said not to worry about any scratches that weren’t deeper than the cross hatch. 

I was thinking that if it was allow to sit and develop rust on cylinder walls, this would result in scoring of the walls on next start.
If ground running, I think this is more likely.

[A64Pilot]

I would be more concerned about the ferrous metal in the filter. I personally have never found any in a piston engine. Only ferrous metal I have ever found was stuck to the magnet in the filter and was so fine it passed right through the filter, looked and felt like a small bit of grease.

I don’t think cylinder scoring is going to carve off bits of cylinder wall to get caught in the filter. What did the chips look like?

I think I’d sacrifice an oil filter in a few hours and likely would put preservative oil in the engine just before the Winter freeze this year if it’s not already happened.

 I don’t think the cylinder scoring is a big concern myself.

You can still continue to do ground runs if you like with the preservative oil if you choose to. Some who go home every Summer where I live put the preservative oil in, leave for the Summer and in late Fall when they return drain it and keep it for next year.