Keeping a motorcycle motor at the correct operating temperature is important to the life of the engine.
If the motor runs too hot, excessive RPM is what will kill the motor as temperature will soar higher & the oil will loose its lubrication properties.
Combined with thermal expansion of pistons, rings etc.
In this situation the edges of the piston crown can start to melt, combined with any carbon deposits glowing; this leads to a pre-ignition situation.
Pre-ignition is then a concern as the temperature ignites the air/fuel mix before the piston reaches top dead centre.
Pre-ignition tries to turn the motor backwards but the combined mass of the moving parts keeps the motor moving in the correct direction.
So there becomes an opposing force which stresses the internals.
Pre-ignition, (detonation) will kill a motor quickly.
This is often a bigger concern for two stroke motors than four strokes.
A motor rising in temperature too quickly can be for a few reasons:
Low oil level resulting in poor lubrication & excessive friction.
Poor oil quality or oil thatâ€™s very old.
Lack of cooling to the motor if its air cooled or in the case of a water cooled motor, the radiator may be too small or lack a suitable size fan.
Blocked radiator creating a lack of coolant flow to cool the engine.
Low coolant level.
Over revving or pulling excessive revs for a period of time.
The motor running too lean, (not enough fuel or too much air).