Cooling Fins

Air-cooled engines have rows of thin fins cast into the cylinder and cylinder head. The fins greatly increase the surface area in contact with air, so heat from combustion is carried away by the airflow as you ride. Oil-cooled and liquid-cooled engines rely mainly on oil or coolant and radiators, though many still have fins for looks or extra cooling.

Air cooling works well while moving, but in slow traffic or on hot days temperatures can rise quickly, so don't let an air-cooled engine idle for long periods standing still.

Keep the fins clean – caked mud or dirt insulates the engine. Bent fins can be carefully straightened; broken fins on the head may cause hot spots, and rubber anti-vibration blocks between fins stop ringing noises.