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Permalink Reply by John Austin on February 10, 2013 at 7:07am

Update - I've been doing a bit of research: Got quite a bit of info from the Jabiru Engine group on Yahoo. Although Mike Busch recommended a used dental camera, he's dealing with Lycomings and Continentals with big plugs and therefore generous-sized spark plug holes for access! Our Jabs and Rotaxes use 12mm plugs - looks like 99% of the dental cameras won't fit or if they do, they are rigid and there would be no room for maneuvering in the cylinder.

The cheaper flexible scopes at Harbor Freight and Home Depot (Milwaukee Brand) are also too thick for the 12mm hole. (By the way, I already had HF's cheapest scope - sometimes you can get it for $79 with a coupon! - and it is fine for looking in nooks and crannies in the fuselage,etc!)

Apparently, the way to go is a 5.5mm flexible videoscope. They usually come with a 1 meter cable, have a CMOS camera on the tip and LED's for lighting. As they go up in price from sub-$200 to about $500 for "entry level" (but useable!) scopes, you get more features like ability to record images, video, write to SD card, USB to computer, video-out to monitor, etc. They typically have 2.5 to 3.5" color monitor screens included.

An inexpensive alternative is a video camera that goes straight to the USB on your laptop - these typically don't have all the bells and whistles of the more expensive units in the last paragraph.

It does appear that a mirror for a 90 degree viewing angle is necessary for complete inspection of the cylinder. There are articulating scopes available, but then you're in the thousands of dollars price range!

Anybody used one of these 5.5mm scopes?

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Permalink Reply by John Austin on February 13, 2013 at 12:09pm

Update - Found some good reviews on this scope:

It's a 5.5mm x 1M scope with a 3.5" color monitor. Brand in UK is "Draper" and in USA is "Voyager Snakescope." It's made in China, of course, as are virtually all of the videoscopes.  It'll record pictures, video and output to an external monitor, USB, or on-board SD card. You can attach a mirror for 90 degree viewing angle. It's $500 plus shipping most places, but I found a new one on Ebay absolutely identical minus the brand name for about $340 including shipping from China. The mirror/hook/magnet kit is about $15-$20.

One person said that the LED lighting was a little marginal in the cylinder for best visibility. His solution was to make a drop light from a clear/white LED powered by a 9v battery and drop that down the other plug hole for supplemental lighting.

I decided to bite on this and we'll see how it works out. I'll have to be patient, though - it's Chinese New Year holiday and nothing happens over there 'til that's over!

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Permalink Reply by david shrader on February 17, 2013 at 3:11am

Hi John,
I won't say borescope isn't a good idea but after doing literally thousands of comp. checks over the years I can disagree with mikes assumption that a differential compression check dosent yeld excellent results. A comp. tester in the hands of a experienced A&P will correctly show the health of a cylinder. Although a borescope can yeld a result its very subjective as to what your looking at. For instance you see a exhaust valve with a lot of carbon buildup and a greenish discoloration around the circumference what do you do with that information, the engine has 500 hrs. T.T. and pulled a 80/80 comp check. (that's a great cyl. assy.) I would argue a borescope would introduce much unwanted and unneeded information into the scope of a engine inspection. If a cylinder failed a comp check how can you be sure it's not ring alignment ......shucks..... First off a borescope won't be able to see that (the expensive shop borescope can't do that) but some simple checks can lead to the correct problem with a low jug. 1. Where is the air going? Crankcase, exhaust, or intake. (this is done with the comp. tester hooked up) 2. What was the last comp. number? 3. What is the comp. numbers of the other cylinders. 4. How much time and what's the condition of the eng.
Leaking valves can be staked if they don't come up simple..... Replace. Back to the ring alignment, since the rings do move in there groves they do occasionally align but not for very long glazed cylinder walls, collapsed rings, ect will give a lot of hints there is a real problem, plugs fouled, plugs oil soaked, excessive oil consumption, excessive breather blowby, low compression check! Ring alignment wont do these things. Save your cash on the borescope. Next to the differential compression tester the only thing that I can see that can help determin the health of a cyl. is individual E.G.T. probes. Mike says "mostly luck" maybe in his hands, but the guys I work with its all skill.
We do use the borescope regularly on the PT6s an the Garretts and in those cases it's the only way to deturman the condition of the engine and is the right tool for the job.

Just my .02 but take it from a old hand, k.i.s.s.
Dave

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Permalink Reply by John Austin on February 17, 2013 at 7:26am

Dave, all good points ... I hear a voice of experience!

However, I didn't say the compression leak-down isn't a good idea, either. I think it's an excellent diagnostic test as you point out. I'm not speaking for Mike, but my take of his webinar was that in a normally operating engine a low compression test shouldn't cause someone to automatically pull a cylinder.

As far as a low compression leakdown test probably due to ring alignment, I think the path I would take would be to borescope hoping not to see anything obvious such as some bad scoring of the cylinder wall, etc., then, I'd button it up, run it, and repeat the test before doing anything else.

I guess I'm biased towards using a borescope because of my medical background. I was one of the first surgeons in Memphis to operate through a scope decades ago and then advanced on to lasers and all the other gee-whiz stuff. Scopes not only let you see things where you normally can't, they also magnify and allow image capture for comparison. So, I see it as a complementary test - might be reassuring with marginal compression tests and let you run that cylinder safely and observe what happens - might show obvious abnormal heat pattern or even a damaged exhaust valve and you pull it right then and there  - might tell you nothing, but hey, you tried!

I think if one does their routine compression leak-down tests and routinely borescopes, it'll be an interesting learning experience, at least, so I'm going to see what I can learn! I already have a cheapy HF scope (too big and not suitable for borescope!) that I've  found very useful. Once, I thought I might have punctured an installed fuel tank with a drill and I scoped the tank (it was fine!) and I was able to sleep that night - much easier than filling the tank and waiting for a leak! HA! I also have used it to retrieve errant screws and washers in the airframe. It's even handy for mundane tasks such as looking behind the dryer in the bathroom closet to position the exhaust hose from kinking! Like a lot of other tools, you wonder how you got along without it and you use it for things you never even thought of previously.

So, I'm going to get a better scope with a skinnier snake (5.5mm) and see what I can learn! As I posted elsewhere, building and maintaining an airplane is a great opportunity to buy more tools! HA! (By the way, my compression leak-down tester was delivered yesterday!)

Thanks for your advice and insight   - John

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Permalink Reply by Larry Zepp on February 17, 2013 at 5:43pm

Hi John,

I use a Rigid Tool "See Snake" at work that uses a small cell phone camera and LED on the end of a flexible cable. The smaller model will fit in a 12 mm and they include a angle mirror for side viewing. This costs about $ 250 and includes a color LCD screen - much cheaper that an aircraft borescope.

 

For larger spaces - like inside wings and fuselage, General hardware sells an attachment that plugs into a laptop USB port, is about 13 mm dia. and costs only about $ 60.00.

Best Regards,  Larry Zepp 

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Permalink Reply by david shrader on February 18, 2013 at 1:05am

No problem John,
Just take what you see with a grain of salt especially if the cyl. comp. check is within engine manufactures limits. Experience...... Ugh I've checked thousands and replaced hundreds, lol it's become a game in the shop with the old guys, Who can trouble shoot it correctly the quickest.
Take care when you try the comp. tester the first time (hang on to the prop. tight) a little bit off tdc will spin that prop. hard enough the seriously hirt a guy. Good luck in your endeviours.

Dave

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