As we mentioned earlier, a four-stroke engine has many moving parts and virtually all require lubrication. We tend to think only the pistons and crankshaft require lubricating oil, but these two components are just the at the very tip of the iceberg.

READ HERE: How does a four-stroke engine work?

There are crankshaft journals and bearings, the connecting rod's small end, the camshafts and its lobes, the finger followers, and in the case of motorcycles, the transmission and clutch, too. So how does oil get to these places? As you can imagine, oil needs to be circulated around the engine and not just at the bottom to lubricate the crankshaft. The valvetrain is on top of the engine, thus the oil needs to get up there.

There are two types of lubrication systems.

Wet sump lubrication

There is always oil in the sump/oil pan at the bottom of the engine, and has a single oil pump. Being near the crankshaft, oil is picked up by oil splashers on the crankshaft and er... splashed on the crankshaft and parts near it, including under the piston(s). In the meantime, the pump takes some oil and distributes it to other parts such as the head through oil passages. This is the traditional method - simple and expensive - but it has major drawbacks, especially being unable to circulate enough oil at higher RPMs.

Dry sump lubrication

A dry sump means oil from the sump is sucked out almost entirely and circulated around the engine. As such, the oil reservoir may or may not be at the bottom of the engine. There are jets situated around the engine, including one underneath the piston to shoot oil to cool and lubricate the small end bearing. There are several jets in the head to shoot oil at the camshaft, lobes and top of the valve stems, too.