The installation relative position of camshaft and crankshaft is unreasonable, because the timing mark is wrong or the belt is loose. Adjust the timing mark or tighten the belt.

camshaft

Camshaft is a component of piston engine. Its function is to control the opening and closing of the valve. Although the speed of the camshaft in a four-stroke engine is half that of the crankshaft (in a two-stroke engine, the speed of the camshaft is the same as that of the crankshaft), it is still very high and needs to bear a lot of torque, so the design requires high strength and support of the camshaft, which is generally made of special cast iron and occasionally used forgings. Because the law of valve movement is related to the power and working characteristics of the engine, the design of camshaft plays a very important role in the design process of the engine.

location

For a long time before, the most common internal combustion engine was the bottom camshaft. Usually in such an engine, the valve is located at the top of the engine, which is the so-called OHV(OverHeadValve) engine. At this time, the camshaft is usually located at one side of the crankcase, and the valve is controlled by the valve mechanism (such as tappet, push rod and rocker arm). Therefore, the bottom camshaft is generally also called the side camshaft. This kind of engine, the camshaft is far away from the valve, and each cylinder usually has only two valves, so the speed is usually slow, the ride comfort is not good, and the output power is relatively low. However, the engine with this structure has excellent output torque and low speed performance, simple structure and convenient maintenance.

structure

The main body of the camshaft is a cylindrical rod with the same length as the cylinder bank. A plurality of cams are sleeved on it for driving the valve. One end of the camshaft is the bearing support point, and the other end is connected with the driving wheel.

The side of the cam is egg-shaped. The purpose of its design is to ensure the full intake and exhaust of the cylinder, specifically, to complete the opening and closing of the valve in the shortest possible time. In addition, considering the durability and smoothness of the engine, the valve should not have too much impact during the opening and closing action because of the acceleration and deceleration process, otherwise it will cause serious valve wear, increased noise or other serious consequences. Therefore, the cam is directly related to the power, torque output and running smoothness of the engine.

Generally speaking, in an in-line engine, one cam corresponds to one valve, while in a V-engine or horizontally opposed engine, every two valves share one cam. However, due to its special structure, rotary engines and valveless valve train engines do not need cams.

boss rod

Crankshaft is the main rotating part of engine. After the connecting rod is installed, it can undertake the up-and-down (reciprocating) motion of the connecting rod and turn it into a circular (rotating) motion. It mainly includes a main journal and a connecting rod journal. The main journal is installed on the cylinder, the connecting rod journal is connected with the big end hole of the connecting rod, and the small end hole of the connecting rod is connected with the cylinder piston. It is a typical crank-slider mechanism. The key technology of crankshaft heat treatment is surface strengthening treatment.