Affects of elevated operating temperatures
Too much heat is bad news for the engine because of the damage it can cause. One of the first symptoms of overheating may be detonation (spark knock). An audible pinging or rattling as the engine strains under load may be a signal that there’s too much heat building up in the combustion chambers.
Piston scuffing can occur if the pistons get too hot, and valves (on a 4 stroke) can stick if the stems overheat and run out of clearance in the guides. Thermal overload also puts tremendous stress on the Alloy cylinder head. If these conditions continue late into a Race then there is a real chance of the piston seizing in the bore
Lubrication is another area that will suffer as a result of overheating. The viscosity of the oil gets thinner as the oil heats up, and if it gets too hot it can start to oxidize (burn) causing a breakdown of the lubricant. The parts most likely to suffer are the rod bearings, rings, cylinder walls, valve guides and upper valve train components. The clutch effectiveness can also be affected in a current generation race bike if the Lubricant becomes too hot.