Borescope #3 - Any comments?

[Dean Pichon]

I have very limited experience with bore-scoping an engine, but just looked at mine while the local A&P inspected it for me.

What another poster described as "scratching" I thought was "cross hatching". It looked similar to what I saw on my engine (~1000 hrs TTSN). The mechanic said cross hatching is good. It helps to keep oil on the cylinder walls.

The lead deposits on your engine looked a bit worse than we found on mine a year ago. I used TCP for a full year and when it was bore-scoped a couple of weeks ago, it was significantly improved. (I plan to continue to use TCP - at least for now)

I'm sorry I have no basis for assessing the valve edges or oil on the piston.

Good luck.

Dean

[no7rosman]

Thank you for the information. It is helpful.

Based on everyones responses it doesn't appear to be a real serious problem and the pictures do not show anything terribly abnormal.

I am going to do another scope and look at the scratches again, and will also do another compression test. If the compressions are good...Guess I'll just fly it.

Will also take a close look at the rest of the cylinders to see if they look any different.

[pa38112]

You did not say if this is a carbureted or injected engine. When you lean, does that cylinder peak last?

[rongawer]

Originally Posted by no7rosman

I am going to do another scope and look at the scratches again, and will also do another compression test. If the compressions are good...Guess I'll just fly it.

Will also take a close look at the rest of the cylinders to see if they look any different.

I agree with your course of action.

I couldn't see a lot of your cylinder walls in the video, but what I did see looks good to me; you have good cross-hatching (which comes from the cylinder honing process) and some minor vertical lines (most likely oil streaking) - all very normal. Assuming compressions are good (and by that, I mean within about 10% of the other cylinders), I'd just fly it and consider what you have as normal.

But do check into fuel distribution, cylinder cooling and temperature bayonet distances. If you have an overly rich or lean supply to #3 compared to the other cylinders, that could cause it to run cooler - EGT's would be the primary indicator of this. If you have excess cooling to #3 compared to the others, CHT would run cooler. If your temp bayonet is farther down the exhaust pipe than the other cylinders, this would cause EGT temps to run cooler, but CHT's would not be affected - however you could pull the CHT bayonet, clean it and reinstall with a good nickel anti-seize to ensure good seating for more accurate temps.

[no7rosman]

It is carbureted. I generally lean by the temps and don't run lean of peak. I lean until the CHTs are at about 350-375. #3 is always cooler. EGT's will be about 1300-1350. At 2300 rpm and 8500 feet she burns about 8 gph.

[no7rosman]

Ron - Thanks for this info. On the EGT's 1&2 always run higher than 3&4 by about 100 degrees. 1&2 are usually very close and 3&4 are usually very close. The probes are not in the exact same spot on each tube. Measurements have shown up to 1/2 inch difference.

I did rule out cowling and baffeling because it happens on the ground. Once she warms up to about 275...#3 will stay down there and the others will climb. Also visible during run up.

A little off subject...the EGT's actually all run pretty consistent on climb out, then after lowering the nose and going fast they stretch out as noted above.

Thanks again. I'll look in to the fuel distribution.

[rongawer]

Originally Posted by no7rosman

A little off subject...the EGT's actually all run pretty consistent on climb out, then after lowering the nose and going fast they stretch out as noted above.

That makes sense; at higher power, you have higher mass flow rates going by the probes with higher energy being carried farther down the exhaust, so the temps will be more consistent, but at lower powers, less fuel being burned, the variance in probe position will be more relevant to variance in temps with the farther probes having the lower temps.

glad to help.