A multi-shaft engine is a type of piston internal combustion engine equipped with multiple crankshafts. The multi-shaft construction enables the realization of single-piston, two-piston (engine with counter-rotating pistons), and multi-piston engines.

A multi-shaft engine is always equipped with more than one crankshaft. According to the number of shafts, this motor is more precisely called, for example, a two-shaft motor, a three-shaft motor, a four-shaft motor, and so on.

An X engine is a four-cylinder or four-row single-shaft piston internal combustion engine. The cross-section of the X engine forms the shape of the letter X, hence the name.

An X engine is a special type of radial engine, but if it has only four cylinders, it is also a flat engine.

A diesel engine is a piston combustion engine that often burns diesel fuel and converts thermal energy into mechanical work. Thermal energy is obtained in the engine by converting fuel into heat through combustion.

When fuel is burned, the temperature and pressure in the engine increase. The increased pressure of the working substance acts on the pistons of the engine, which convert this energy into mechanical work.