A cam engine is a reciprocating engine where instead of the conventional crankshaft, the pistons deliver their force to a cam that is then caused to rotate. The output work of the engine is driven by this cam mechanism.

A variation of the cam engine, the swashplate engine (also the closely related wobble-plate engine), was briefly popular.

Cam engines are generally thought of as internal combustion engines, although they have also been used as hydraulic and pneumatic motors. Hydraulic motors, particularly the swashplate type, are widely and successfully used. Internal combustion engines, though, remain almost unknown.

The mechanical design of a cam engine differs from that of conventional crankshaft-driven internal combustion engines. The engine's design incorporates a cam mechanism instead of a crankshaft, presenting distinctive challenges and opportunities for enhancing performance.

The history of cam engines is connected to the development of engines, especially in the late 19th and early 20th centuries. Engineers and inventors explored different mechanical designs to improve engine performance. One of the earliest recorded cam engine concepts dates back to the 19th century, during the Industrial Revolution.

In 1862, a French engineer named Alphonse Beau de Rochas, who is credited with the four-stroke engine, also explored using cams in engines. His work laid the foundation for later developments in internal combustion engines. Another notable figure is Felix Wankel, the German engineer known for inventing the Wankel rotary engine. Wankel's work on unconventional engine designs included experiments with cam-based mechanisms, although his rotary engine became more prominent.

In the early 20th century, many patents were filed for different cam engine designs. These designs were especially important for aviation and industrial applications. During World War I and World War II, there was a lot of interest in alternative engine designs, with various advantages in power-to-weight ratio, durability, and fuel efficiency. However, cam engines never became widely used. This was mainly due to the complexity of their design and durability issues with the cam and follower mechanisms.

The cam mechanism is central to the cam engine, playing a crucial role in converting the linear motion of the pistons into rotational motion—a task traditionally carried out by a crankshaft in conventional engines. The cam, a rotating or sliding component within a mechanical linkage, imparts the desired motion to a follower through direct contact. In the context of a cam engine, the cam is typically configured as a rotating disk or cylinder with a specially shaped profile that interacts with the pistons, carefully engineered to control the timing and movement of the pistons as they reciprocate within the engine's cylinders. As the cam rotates, its profile exerts pressure on a cam follower, causing the follower to move up and down along the cam surface, transmitting this motion to the pistons, thereby driving their reciprocating motion. The shape of the cam determines the piston's stroke length, timing, and speed, directly impacting the engine's performance characteristics. In a cam engine, the cam is linked to a drive mechanism, usually a shaft, which rotates the cam at a specific speed synchronized with the engine's combustion cycle to ensure the pistons are correctly positioned to harness energy from the combustion process. The meticulous design and synchronization of the cam mechanism are vital for the efficient operation of the engine, as any deviation can result in performance issues or mechanical failure.