Internal combustion engines convert potential chemical energy in the form of heat derived from a fuel into mechanical energy. Approximately 30% of the energy released in an internal combustion engine is converted into work. The remaining energy is lost in the form of heat and friction in the engine. Engine components are designed to convert energy in an internal combustion engine for maximum efficiency. Materials used for engine components must withstand heat and stress generated inside the engine during operation, and meet size and weight requirements. Engine components commonly required in reciprocating engines include the engine block, cylinder head, crankshaft, piston and piston rings, connecting rod, bearings, flywheel and valve train.