Question about using borescope to check exhaust valve guides on Lycoming IO-360

Ive been skeptical about using a borescope to check exhaust valve guide wear on Lycoming IO-360s without pulling the cylinder but after a few years of trying it on 15 engines I found 3 cases where the scope clearly showed scoring that matched a wiggle test later. The trick was using a 90 degree mirror tip and looking at the guide wall at a specific angle past the valve stem. Anybody else found this method reliable or do you still pull cylinders for that inspection?

2 comments

2 Comments

tyler_baker3d ago

Yeah, I used to think borescopes were useless for that, but this changed my mind.

val_taylor3d ago

Honestly, a cheap one saved me pulling a head off a dead engine last month.