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.
So, what are the cracks, what caused them, will it shorten the cylinder life, is there a cause of premature engine failure?
That is the normal appearance of a chrome cylinder. That is just the way they look. From what I understand those “channels” are what help lubricate the steel rings used with chrome cylinders. Steel cylinders use chrome rings and chrome cylinders use steel rings.
Thanks Paul. Really appreciate the info