The coupling parts of the nozzle is one of the three precision coupling parts of the traditional diesel engine, including plunger, plunger sleeve, needle valve, needle valve body, oil outlet valve and oil outlet valve seat. The nozzle of gasoline engine is a part of electronic control system of gasoline engine, which replaces the carburetor of carburetor type gasoline engine. The main nozzles used in automobiles include diesel nozzle, gasoline nozzle, natural gas nozzle, etc. now some foreign manufacturers can manufacture special nozzle for hydrogen.

In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings. The bearings hold the crankshaft in place and prevent the forces created by the piston and transmitted to the crankshaft by the connecting rods from dislodging the crankshaft, instead forcing the crank to convert the reciprocating movement into rotation.

While some small single-cylinder engines have only one main bearing, designed to deal with the bending moment exerted by the crank as a result of the force from the connecting rod, most engines have at least two main bearings, one at each end of the crank shaft and may have as many as one more than the number of crank pins. Increasing the number of bearings in an engine will generally increase the size and cost of the engine, but also provides stability to the crankshaft, which would otherwise have to endure greater bending moments from having the crank pin further from a bearing. The combination of bearing number and crankshaft design can also have an effect on engine balance; a more stable crankshaft will better avoid unbalance from flexing, but increasing the crankshaft length or girth to accommodate an additional bearing increases the rotational inertia of the crankshaft, which can have the opposite effect.