Borescope #3 - Any comments?

Hello,

My #3 has burned cooler than the rest since I bought the plane. The temp difference is around 50-70 degrees. 1, 2, 4 all seem to run pretty similar. I ruled out the sensor.

Just wanted to see what people thought of the borescope. Specifically the oil on the top of the piston, and jagged edges on the valve. (last shot)

https://www.youtube.com/watch?v=9W0mtd2OG-8&feature=youtu.be

My airplane uses lightspeed ignition with automotive plugs on top and mags with aircraft plugs on the bottom. Top plugs look new. The bottom is a bit oily but not fouled.

Thanks,
Ross

How many hours do you have on that engine?

~500 hours

Nice images. Could you please post what scope set up you are using? Sorry I don't have any experience reading the images.

There is nothing in the vid that would lead me to a conclusion regarding temperatures.

Are you talking CHT or EGT? They are quite different indications and the EGT is very sensitive to location and installation variables. The relative changes are what you would use for EGT unless it is hundreds off.

Sensor accuracy would be the first thing that comes to mind of one CHT is way different. That should be checked first. (it seems you did)

An important measurement is the leak down test. Although that exhaust seat looked bad, I think the camera angle was looking parallel to the seat contact area. The "heat ring" on the head looked concentric. Leak down is a more definitive parameter at this point.

The cylinder walls look scratched, maybe operation from dirt and/or grass strips or an area with sand/dust storms?

Last parameter checks are oil consumption and oil sample analysis.

Please let us know what temperature you are measuring and a little more on the other items if you have it.

It looks like the video is no longer available. I am not able to view it on youtube

Assuming you mean CHT (EGT numbers don't matter much in this context). Is your engine fuel injected? If so, what is the GAMI spread?

Bavafa said:

It looks like the video is no longer available. I am not able to view it on youtube

Click to expand...

Try it again, I can still see it.

There is one spot on the piston that looks like the crown is chipped/pitted? Or is that just deposits on the crown flaking off? The vertical stripes on the cylinder together with those spots on the piston made me think of a broken oil ring.

Hello all,

Thank you for help on this.

I am measuring CHT. I checked the probes by switching 1 & 3 and got the same results.
I then put a new probe in for good measures.

It is carbureted.
Oil usage is not too bad but does use some. About 1 qt. Every 10-15 hours.

I’ll do the leak down test ASAP.
I’ll get the bore scope model when back to the hangar

Looks good to me

The build up on the piston is normal, especially if you've used any leaded fuel. Your exhaust valve has a nice pizza-pie appearance, which indicates good rotation. Your intake valve looks good.

How are your compressions? Irrelevant of that, as much it would be nice to have all CHT's about the same, a 50-70ºF difference is still not horrible. Note that exhaust temp drops very quickly as exhaust moves downward in the pipe; a minor difference in distance from the exhaust valve can result in the temp variance you're seeing.

The most likely factors affecting CHT are fuel distribution, cylinder cooling and temp bayonet location.

Compression would be a more immediate indicator of a piston or valve issue.

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

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.

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

no7rosman said:

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.

Click to expand...

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.

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.

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.

no7rosman said:

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.

Click to expand...

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.