Spinning thousands of times per minute, they control your bike’s valves ‘It has to happen at precisely the right time so the engine runs sweetly’
Tony has worked for Kent Cams (www.kentcams.com) for 31 years and has been designing performance cams for World and British Superbike race bike teams for more than a decade. He used to race Yamaha a RD250LC and The job of a camshaft is to open the inlet valves to let air/fuel in, then open the exhaust valves to let the spent fuel out. This all has to happen at exactly the precise moment, so the engine runs well and the valves don’t hit the pistons as they shoot up the cylinder.
In most modern engines, the camshaft is turned by a belt or chain connected to the crankshaft. As it turns, protrusions called lobes push down on the valve train.
The height of the lobe determines how much the valve is pushed down and is called lift. Then there is duration, which is how long the cam holds the valve open and is determined by the nose of the lobe. Then there are the opening and closing clearance ramps, which are the sides of the lobe and determine how quickly the valve is opened. Finally there is overlap, which is the time when both the inlet and exhaust valves are open at the same time, which changes the torque characteristics, especially in twin-cylinder engines. All these factors can be tailored but there is always a compromise between where the power is required and how much stress is put on the valve train.
This chainoperated cam is from a BMW boxer