Compression Checks, borescopes and SB03-3

[mhorowit]

Earlier this week I got the bright idea that I could do a compression check on an engine; after all, I still had the compression gauge from my ’63 Chevy, and with my welder, I could build an adapter from and old sparkplug.

Wrong.

A few minutes GOOGLING turned up what the numbers ment and how they were derived via a ‘differential pressure check”. My search also pointed me to TCM’s SB03-03 which says in effect you must do a borescope inspection in conjunction with each compression check. Actually, at http://www.avweb.com/news/columns/188758-1.html
It says “If your shop doesn't have a borescope, it cannot legally perform a compression test on a TCM engine.”

Question: During your last annual, did you see a borescope in use?

[Garry Crookham]

Re: Compression Checks, borescopes and SB03-3

Mike,

SB03-3 has stirred up a lot of discussion. Some very knowlegeable mechanics state that SB03-3 is mandantory, others feel that since it is a service bulletin, compliance is not required for Part 91 aircraft.
I work for an FAA approved repair station, and per our repair station manual, SB03-3 is mandantory for us. I also maintain several Part 91 aircraft outside of my employment at the repair station and do use a borescope during compression checks for the following reasons:
1. I own a borescope and because I am familiar with its use, and use it all the time, I have found it to be a very useful tool.
2. Due to an experience I had while ferrying a Bonanza from Norfolk to Tulsa a couple of years ago, I have opted to make borescope inspections of cylinders a required inspection item during any 100 hr/annual/ compression test/spark plug removal. ( Number 2 cylinder on the Bonanza developed a cracked head..through both upper and lower spark plug holes, exhaust valve seat came loose, I was lucky and ATC was able to put me on the ILS into Lewisburg West Virginia before the head separated. I'm convinced that a borescope inspection would have revealed a crack long before the incident occurred.
In summary, is a borescope inspection required for Part 91 aircraft? My opinion is probably not, but if one is available I feel is would be very desirable to use it. I use it on my Taylorcraft and Fly Baby, have never found a problem on them, but will continue to look.
If anyone has a desire to peek into their cylinders, fly to RVS and use my borescope free of charge.

Garry Crookham
N5112M
Tulsa

[hangarb7]

Re: Compression Checks, borescopes and SB03-3

Garry,

So what all do you look at or for when you use the borescope?

Just cracks or are there other tell-tale signs?

No borescope used on my compression check / first annual.

Jack

[mhorowit]

Re: Compression Checks, borescopes and SB03-3

Garry,

So what all do you look at or for when you use the borescope?

Just cracks or are there other tell-tale signs?

No borescope used on my compression check / first annual.

Jack

Jack - Google for 'SB03-3'.
the Bulletin has pictures in it as well as a good description of both the pressure testing and the borescoping - Mike

[Garry Crookham]

Re: Compression Checks, borescopes and SB03-3

Jack,

As Mike has indicated above, SB03-3 has some good pictures representing various problems that can be viewed by the use of a borescope. I've found chrome peeling from cylinder walls, deep scratches that were caused by a broken ring, and various kinds of valve problems.
I feel that a compression test by itself doesn't give a true representation of the condition of a cylinder, and I wouldn't pull a cylinder due to a low compression reading if I didn't have supporting data. Many times we have a cylinder with a 40/80 differential compression reading and leaking by a valve. Using a borescope, we can determine if the valve is leaking in a dynamic condition...engine running....by viewing the pattern around the valve, as shown in the service bulletin. If we have valve blowby only in a static condition, no action is necessary, which could not be determined by a compression test alone.
A good borescope is expensive, I paid $800 for mine, and you can pull a bunch of cylinders on an A-65 for that amount of money (assuming you do the work yourself), so I can understand why many people would balk at the cost of a borescope. My suggestion is that if you encounter low compression readings try to beg, borrow, or use some other means to find a borescope to look and see what's going on, if possible. It might save you from removing a good cylinder, or point out defect that needs correcting.

Garry Crookham

[mhorowit]

Re: Compression Checks, borescopes and SB03-3

Gary - There are small borescopes for about $185, but the fiber optic can't be moved while in the cylinder i.e. can't bend it into a 'U' while in the cylinder. One can, however, bend it outside the cylinder and then insert it.
Have you had any experience with these? - Mike

[Howard Wilson]

Re: Compression Checks, borescopes and SB03-3

One can, however, bend it outside the cylinder and then insert it.

Hope no proctologists are reading this

[Garry Crookham]

Re: Compression Checks, borescopes and SB03-3

Mike,

I've used a couple of the inexpensive borescopes without much success. My borescope is a Lennox...the same model as shown in the service bulletin...and am very pleased with it.

Garry

[flybikefarm]

Re: Compression Checks, borescopes and SB03-3

gary do you ever go to the chilli bowl? one of my primary students is out there racing this week. george

[flyguy]

Re: Compression Checks, borescopes and SB03-3

Might be a good investment to rent a borescope once a year just to check things out. If you can find someone with one who will check your engine or let you do it (?) I think I will do just that this time around. Good input Garry.
DC

[Yellow Duck]

Re: Compression Checks, borescopes and SB03-3

Whenever I need some special tool or instruction on something, I go to the A & P School here. they have borescopes, electronic scales, Nice paint booths'. And all kind of goodies.

Locate one in your area, they normally are more than happy to help.

Also with the new LSP Repaiman License. Only 120 hrs. Then you are able to do your annual ,and sign off your work. Get full detail. And become a friend of the local school. It works, and can be another source of information.

[mhorowit]

Re: Compression Checks, borescopes and SB03-3

Also with the new LSP Repaiman License. Only 120 hrs. Then you are able to do your annual ,and sign off your work. Get full detail. And become a friend of the local school. It works, and can be another source of information.

Is the LSP Repairman License a done deal with course of study and all? I thought they were still trying to determine what should go into it - MIke

[mhorowit]

Is there a 'second best' way to check compression?

Assume you don't have access to a differential pressure tester(and source of compressed air), is there any way to judge how well a cylinder is holding it's pressure? or is it the sort of thing where you say 'don't even bother' - Mike

[alwaysoar]

Re: Compression Checks, borescopes and SB03-3

"The Savvy Aviator #13: Putting Compression in Context" gives a very good analysis of SB03-03. It's great reading in fact. I don't have the address, but I'm sure your search engine can find it. SB03-03 is "guidance" and does not seem to actually require a boroscope inspection. What it does is liberalize what the results of a compression check mean and it supercedes the FAA 60/80 guideline found in AC 43-13b. An older man I know just got hosed by an A&P who pulled two cylinders because they came out under 60/80--cold. Correct me if I'm wrong (I don't have it in front of me), but I believe SB03-03 says do compression checks on a hot engine.

[mhorowit]

Re: Compression Checks, borescopes and SB03-3

"The Savvy Aviator #13: Putting Compression in Context" gives a very good analysis of SB03-03. It's great reading in fact. I don't have the address, but I'm sure your search engine can find it.

It is a very good article; it's what led me to SB03-3 - Mike