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Old 12-08-2019, 05:53 PM
no7rosman no7rosman is offline
Join Date: Aug 2018
Location: Johnstown
Posts: 54
Default Borescope #3 - Any comments?


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)

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.

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Old 12-08-2019, 07:01 PM
drone_pilot drone_pilot is offline
Join Date: Jan 2014
Location: Hobbs, NM
Posts: 241

How many hours do you have on that engine?

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Old 12-08-2019, 07:37 PM
no7rosman no7rosman is offline
Join Date: Aug 2018
Location: Johnstown
Posts: 54

~500 hours
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Old 12-09-2019, 04:21 AM
rvmv rvmv is offline
Join Date: Nov 2017
Location: Crystal River Fl & Rabun Gap Ga
Posts: 66

Nice images. Could you please post what scope set up you are using? Sorry I don't have any experience reading the images.
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Old 12-09-2019, 08:17 AM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,320

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.


Last edited by BillL : 12-09-2019 at 08:19 AM.
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Old 12-09-2019, 10:25 AM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,639

It looks like the video is no longer available. I am not able to view it on youtube
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Old 12-09-2019, 10:28 AM
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Raymo Raymo is offline
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Location: Richmond Hill, GA (KLHW)
Posts: 2,340

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?
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Old 12-09-2019, 10:30 AM
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airguy airguy is offline
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,593

Originally Posted by Bavafa View Post
It looks like the video is no longer available. I am not able to view it on youtube
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.
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Old 12-09-2019, 10:39 AM
no7rosman no7rosman is offline
Join Date: Aug 2018
Location: Johnstown
Posts: 54

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
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Old 12-09-2019, 11:35 AM
rongawer rongawer is offline
Join Date: Dec 2007
Location: Brentwood, CA
Posts: 775
Default 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.
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