Question for Paul McBride, the General Aviation News engines expert: I recently bought a borescope and used it on my neighbor’s experimental Panther. The engine is an O-320 that had a major overhaul a couple of years ago and has about 100 hours since then. It runs great and the compressions are all 74/80 or better.
But these marks on the bores are really strange. There were no scuffs, just this weird crazing.
Never seen this before. What do you think?
Colin A. Macdonald
Paul’s Answer: Colin, what your new borescope is showing you is a channel chrome cylinder bore. The lubrication factor through those channels is very good and because the surface is chrome, corrosion is never going to be a factor.
The wear capability of chrome cylinders is less than the hardened nitride cylinders more commonly used today, but still offer a good service life when used on overhauled engines.