Part of the annual inspection checklist is to examine the cylinders of a plane for evidence of overheating. This can come from running too lean, baffle seals in poor repair, cooling system leaks, bad baffles, under-cylinders baffles undone or wired wrong, exit ramps that are colapsing or just too small of the engine heat generated (High compression STC, Powerflow, Electronic ignition – all which produce more power and thus, more heat.)

Notice the oil that is burning on the exhaust valve (right most valve) and causing it to be dark brown. In extreme cases it will be black and cooking up due to the oil actually burning and will lead to valve sticking. Valve wobble test will be 0, no wiggle at all. Very bad!

Compare this to a normal exhaust valve (300 hour engine) and a cylinder that only got hot occasionally.

Cylinders that are getting hot may start to have helicoils fail and they will warp, or even come out when you remove a spark plug.

Engine management systems are so affordable today, that if you want to get the most out of your engine, you should install one. What you find may surprise you, even when operating the engine according to experts!