For years I have been reading about the value of a borescope inspection of the cylinders and valves in determining the health of the engine. Borescopes have steadily reduced in cost, and now it is possible to buy a good quality rigid borescope with an articulating head for $200.
Mike Busch wrote about this in his May 2017 Savvy Maintenance article in AOPA Pilot Magazine, and recommended the Vividia Ablescope VA-400 Rigid Borescope. That unit is available from Oasis Scientific or Amazon, and retails for $200 (as of Dec 2017). That particular model of borescope does not include a display device, and requires a computer or mobile device that accepts a USB input device. Essentially, the borescope is treated like a webcam, and the simple software utility from the manufacturer displays the video image, captures screenshot pictures, or records the raw video file from the borescope.
I took the opportunity to use my new borescope in conjunction with a planned spark plug change. The plugs were already out, so why not scope the cylinders and see how they look? I also performed a differential leak-down test, and those results were added to my maintenance records (no problems indicated).
The scope is a bit tricky to use, and requires a bit of manipulation to get the camera pointed at the intended target of interest (such as a particular valve). The USB cord connecting the scope to my laptop also included a button that activates a screen capture of the current image. I found this feature very useful, far more so that the raw video capture. It was easy to move the scope around to find the best shot of interest, then press the button and capture that image. It's easier than re-watching the entire inspection looking for the perfect angle. I sorted each cylinder's photos into a different folder on my laptop, and archived them for later use. You could very easily record the video of the entire operation as well, and 20 minutes of video would still be easily stored on a computer or mobile device, and even archived on youtube if desired.
The results of the inspection showed all cylinders and valves in good condition. The engine has 300 hrs of use, running a mix of premium car gas and 100LL. The piston tops show a bit of crusty white deposits, that appear to be a few thousands of an inch thick. The pictures are deceptive because the focal length of the lens is so short, and objects up close look unusually big. In any case, they did not look particularly worrisome. I did find a few places where lead from the fuel had adhered to a deposit, but less so than other engines running a diet of straight 100LL.
The one area of particular interest was the exhaust valve of cylinder #5. That cylinder is one of my cooler running cylinders, and I surmise that the internal temps are not high enough to burn off the deposits and lead from this valve. I'll continue to monitor it for changes over time.
NOTE: photos link to full size image