Borescope procedure

[Matt Ward]

I'm coming up on my first annual and have requested my A&P borescope my engine.  I say that because of all I read on the ascendancy of the scope over the compression test, but I don't know exactly what I should be looking for.  I mentioned this to my A&P and his reaction is "no problem, we can scope it" but I don't think he's as much of a fervent believer as those in the Mike Busch camp.  I'd like to have some some of standard procedure that we can look at but I'm not sure what all that would be.  

Are you guys aware of any sort of checklist I can use with my A&P to get the most out of the borescope procedure?

I fully trust my A&P, I'm really just trying to educate myself on how we're using this tool.

Thanks!

 

[Vance Harral]

The main thing you're looking for is asymmetric wear patterns on the exhaust valves.  It's possible to catch these early, before the valve actually starts to leak enough to cause lower compression readings.  You get to see the intake valve too, of course.  But my limited understanding (not an A&P) is there's not much to look for on the intake valves other than gross damage.

You can also look at the cylinder walls to see if they still have their cross-hatching, and/or if they're beginning to show any signs of abnormal wear.

For pictures, see the "What to look for" section of https://blog.aopa.org/aopa/2016/12/20/scope-that-jug/

[carusoam]

Ascendency of the scope over the compression....

Hmmmm....

Negative captain.... I think you want them both....

1) Compression = ring health... A standard in Mooney aviation...

2) Pics of all the valves all the way around... = looking for sticking valves...  Pizza vs. not a pizza.... temp distribution...

3) pics of the cylinder wall... = cross hatch health... Pits from corrosion....
 

4) Decision time comes with lack of compression....

5) Valves may be the reason for it...

6) rings may be the reason...

7) Cylinder walls may be the reason...
 

8) It is better to take too many pics, than too few... some of the initial pics we have seen around here didn’t get the whole valve, or just a spot of the cylinder wall...

So many reasons are a cause of cylinder health issues... the more data you have the better...

Best regards,

-a-

[EricJ]

Pretty much covered above, but you can't get out of the compression test because it's required by the regs for an annual or 100-hour inspection (FAR Part 43 Appendix D (d)(3)).   The borescope is not required.

The borescope and differential compression test are both informative, and reveal different things.   The compression test can tell you a lot that the borescope can't.

Since the plugs will be out for the annual, anyway, it's really easy to stick the borescope in and see what you can see.

 

[bradp]

The procedures are complementary and useful. You’re not going to find a broken ring on borescope (necessarily) but you may on a compression test. Alternatively you aren’t going to see a pizzad exhaust valve on compression testing before the valve is shot. 

[Matt Ward]

Thanks guys, that's all very helpful!

[gsxrpilot]

I've got a camera you can plug into a laptop and borescope it yourself while the plugs are out. I'm happy to loan it to you.

[Matt Ward]

Just now, gsxrpilot said:

I've got a camera you can plug into a laptop and borescope it yourself while the plugs are out. I'm happy to loan it to you.

Sweet, yes!  Thank you!  

BTW: i added Canon City to the logbook this am.  Everyone was out flying.  There were four folks in the pattern when I was approaching.  Eight folks in the pattern at BJC when I got back.