Cylinder Liner Characteristics In 4-S Engines

The four stroke engine liners do not require any ports and are relatively simpler in construction as compared to cylinder liners for two stroke engines discussed previously. Instead of ports, a 4-S engine contains valves and the valve timing is controlled by the cams. The upper end of the liner forms a flange of sufficient strength to support it. A flange is secured between the cylinder cover and the jacket or engine and the lower part of the liner is free for thermal expansion.

The liner thickness gives adequate strength to resist the internal gas load but at the same time another factor has to be kept in mind that is the heat transfer capacity. If the liner is made too thick, it would hinder the smooth transfer of heat and hence it would to thermal stresses in the liner. So the thickness has to be kept at an optimum value which is neither too weak nor to thick for effective heat transfer.

In four stroke engines the valves are used for scavenging and exhaust of the residual gases. Unlike two stroke engines, it requires four strokes of the engine to complete the four processes of the engine cycle namely scavenging, compression, power and exhaust.

Thus the valve is placed on the cylinder head and no cut marks are made on the cylinder liner. The sketch below shows a pictorial description of such a cylinder liner and all the parts are clearly labeled therein. Just take a close look at the sketch before studying further, as that would help you to gain a better idea of what is being talked about.