SOHC (single overhead camshaft)

SOHC is divided into two valves and four valves. Today we mainly take the four-valve SOHC as an example.

In the market, the large-displacement performance models have rarely used this SOHC engine, because the common speed of motorcycles is generally high. Only some cruiser retro cars still use two valves despite large displacement. Or the ordinary SOHC engine, this engine is more seen in small displacement models within 250cc, such as Zongshen's NC250 engine, and Yamaha's R15, and the like.

The SOHC structure is simpler than DOHC, but although only one camshaft is transmitted to the four valves through the two-valve rocker arm, the valve opening and closing is controlled.

advantage:

Since only one camshaft is directly driven by the timing gear, the engine's rising speed will not be affected by the rotational resistance of the camshaft, and the output of the low speed portion can be completed more quickly. Low maintenance costs, simple structure, and more economical fuel on low-speed highways.

Disadvantages:

At high speeds, the rocker itself has a certain elasticity, and the reciprocating motion of multiple components produces inertia, so the valve stroke control lacks stability at high speeds and there is some unnecessary vibration or noise.

DOHC (Double Overhead Camshaft)

As the name implies, the DOHC nature is to drive two camshafts that can be rotated directly under the valve through the camshaft. The valve rocker arm is no longer a medium, but requires a longer timing chain or belt drive.

The mainstream mainstream large displacement models in the market are basically using DOHC engines, especially high-performance models! Due to the complexity of the DOHC structure, it also requires high costs to manufacture and maintain.

advantage:

In terms of structure, the stability and accuracy of ventilation at higher engine speeds is better. Give full play to the maximum performance of the engine. Vibration control is better because there are not too many reciprocating components and transfer media. With two separate cams, a V-shaped combustion chamber can be used and the angle of the valve can be designed to be more flexible. The spark plug can be placed in the middle of the combustion chamber and contributes to complete and uniform combustion.

Disadvantages:

Since the two cams are to be driven, the engine's low speed acceleration interval torque will be lost. Due to the complexity of the structure, the cost and difficulty of maintenance will be higher than SOHC.

Combined with the above points

It seems that DOHC is more competitive than SOHC in use, but DOHC is not suitable for all motorcycles.

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