How is the context oil / cylinder head?
The air-cooled motors have no thermostat and no temperature monitoring or control. As measured with our system, the critical temperature on the surface of the cylinder head is 250 ° C. Then the temperature inside the cylinder head is higher.
The problem part is the shrunk valve guides. Either the aluminum cylinder head is strongly heated before the assembly of the valve guides (expands in the process) or the valve guides are strongly cooled (nitrogen – contract). One thing is clear – the guides are only clamped (shrunk).
At a surface temperature of over 250 ° C, the cylinder head is so expanded that the valve guides can slip out. These then slide on the valve stem onto the actual valve. The next time it closes, the guide jams and the valve no longer closes. The piston strikes the valve and the whole motor is blocked. In most cases the valve will tear off and become wedged in the combustion chamber.
What is about oil temperature?
The information of high oil temperature is far behind the actual cause (hot cylinder head). The cause for the overheating can be a simple overload or even dirt in the main jet of the carburetor or a defect of the air cooling. The main jet then lets too little fuel through and the engine runs too lean.
The external oil cooler keeps the oil temperature low – but it does not increase the performance of the oil pump. The amount of oil that the holes let through does not change. Here it can come to a condition that the cylinder head is overheating – but the oil temperature is at 80 ° C (own experience). The oil cooler manages to keep the oil temperature low – but the flow rate to the head does not manage to cool the head down.