Air-cooling is common on smaller internal combustion engines. They may be small but they still generate a lot of heat.
It’s the air that does the work of keeping them cool, so an air-cooling system is usually simple. That’s useful on an engine where weight is important.
And it works best on the engine that’s exposed to a high airflow.
Almost all motorcycles used to be air-cooled but modern motorcycles are larger and more complex, and some are now liquid-cooled.
Some engines use what are called cooling fins. Their design makes the exposed surface area as large as possible, which allows more heat energy to radiate away, and be carried off in convection currents in the air.
More air flows over the fins and more heat is carried away.
For a vehicle moving at speed, airflow over the engine is high.
At low speeds or during idling, heat builds up. Then the engine can use some help.
Air should always be able to flow over the engine effectively.
One way to remove heat is to use a fan, with shrouds and ducts to direct air to the cylinders.
There are many places to mount a fan and many ways to drive it. For instance, in some engines it’s on the flywheel, driven by fan-belts off the crankshaft.
