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’

Motorcycle News (UK) - - Garage - then pro­gressed to TZ250S.

Tony has worked for Kent Cams (www.kent­ 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

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