BETTER LUBRICATION – LESS STRAIN

One of the manifestations of form boring in conrod machining is the introduction of a trumpet contour inside the bush of the small conrod eye. The tolerance range for producing this contour is around 3 – 5 µm.

Advantages of the trumpet contour:

• Improves the piston pin’s lubrication
• Protects the pin from damage
• Reduces the strain on the piston pin

The pin’s lubrication will also be improved in conrods with an elliptical eye. This is because, in an oval bearing, the force from the piston acting on it means that the piston pin will be flattened within its elastic range.

When the pin then returns to its original shape, it creates a suction effect that causes the oil to be “sucked” into the area between the bearing and the pin. This means that a film of lubricant gradually builds up as a result of the capillary effect.