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Shop Talk

July 2016 Issue




Maintenance Matters

Affordable borescope.

Longtime airplane builder Ed Zaleski manipulates the borescope to get the proper image on the computer screen and then clicks the mouse to snap a picture.

How many times have you read that before you tear an engine down after a questionable compression test, you should use a borescope to see the condition inside the cylinders? Mike Busch, among others, has been particularly vocal about not tearing things apart without strong evidence that such drastic action is really necessary. Well, that's great advice, but in the past a borescope was pretty expensive, beyond the means of most casual mechanics, so unless you had a friend with one, it was pretty hard to follow that advice. That has now changed.

This is an exhaust valve as seen through the borescope. The edges of the valve aren't burnt and the color is fairly even across the face of the valve. The yellowish carbon deposits are normal for an exhaust valve.

This is an intake valve as seen through the borescope. It is in good shape with no signs of burning or discoloration. The edge of the exhaust valve can be seen in the upper left corner.

There have been some low-cost borescopes on the market that weren't very good, and there have been some pretty good borescopes available from high-end tool vendors, but it has been very hard to find a good borescope that was also affordable until now. I recently tested the new ViVidia VA-400 Rigid Borescope and found it to be a good way to go for someone who is serious about working on engines, but unwilling to spend big bucks on a tool that only gets used occasionally. The ViVidia borescope is available on Amazon and it presents the user with still or video images that are very clear. Its articulating head folds back 180 degrees on itself, so it is fairly easy to angle it to see all around inside engine cylinders, even the valves.

When I say fairly easy, that needs some qualification. It definitely takes some practice to coordinate the movements of the probe and the bendable camera head to get the field of view where you want it. It can also be a little hard to figure out exactly where you are looking when inspecting cylinder walls, but after a while you get better at it. This is not unique to the ViVidia borescope. It is just the nature of the device.

The lower spark plug shown here looks good. Note the slight pooling of oil below the plug.

A good cylinder wall should have the original hash marks from the honing process still visible. Bare spots without hash marks are an indication of a worn out cylinder.

The ViVidia needs a computer or laptop with a USB connection to work, since it has no built-in screen. It works with most any computer with a USB plug, including Macs and PCs. You just use the web cam or video camera software already in your computer. No special software is needed. The images produced are 640x480 pixels, and the video works at 30 fps. This is not exactly HD video resolution, but it is very clear and useable for its intended purpose.

So, now that you can see inside your cylinders, what are you looking for? The compression test will give you a starting point. If there is leakage past the valves, a thorough inspection of the valves should reveal uneven coloration across the face of the valve, or in bad cases actual burning of the valve. A good valve should appear perfectly round and have even color all across the face of it. If a valve is burnt you have a good reason to remove that cylinder and repair it. If there is leakage past the rings the clues are subtler. In a badly worn cylinder there should be smooth spots in the cylinder walls where the hash marks are no longer visible, or score marks left by a broken ring. If you see these things some cylinder work is in order.

The ViVidia borescope is shown here on a tool table with a laptop computer. The borescope will work with most any computer that has a USB connection. It will not work with an iPad or iPhone however.

Other problems can be seen in cylinders, especially the effects of detonation and pre-ignition. If you look at the spark plug remaining in the cylinder head, you may see exposed threads, either from the spark plug being too long or too short. This is a very likely the source of pre-ignition with a straightforward solution: Install the correct spark plugs.

Detonation, if it goes on very long at all, will leave evidence in the form of pitted or melted piston tops or possibly pitted cylinder heads where the strong

detonation pulses have actually destroyed metal inside the engine. The most likely cause of detonation is incorrect ignition timing, but fuel with an insufficient octane rating can also be the culprit, especially if you are trying to run regular auto gas in an engine with a too-high compression ratio.

Sadly, there is still no way to see the camshaft inside the engine with this or any other borescope. However, you can now get a very good view of the insides of your cylinders without breaking the bank. The ViVidia borescope is a great tool at an affordable price.


Dave Prizio is a Southern California native who has been plying the skies of the L.A. basin and beyond since 1973. Born into a family of builders, it was only natural that he would make his living as a contractor and spend his leisure time building airplanes. He has so far completed three—a GlaStar, a Glasair Sportsman, and a Texas Sport Cub—and he is helping a friend build a fourth, an RV-8. When he isn’t building something, he likes to share his love of aviation with others by flying Young Eagles or volunteering as an EAA Technical Counselor. He is also a licensed A&P mechanic and a member of the EAA Homebuilt Aircraft Council.

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