The following video provides an overview of the aircraft piston engine. The video focuses on airplane, but would be applicable to the piston engines used in helicopters as well.

The following video provides additional information related to the oil system on a piston engine.

Although the following video is related to airplane, the principles apply to helicopters as well.

The following is a good animation of how the carburetor works.

In addition to reciprocating engines, there are also turbine engines.

Turbine Engines

The following video provides and overview of the turboshaft engine.