2585386 - Introduction - TIMING SYSTEM

The timing system is the collection of components which control the opening and the closing of the inlet and exhaust valves allowing the flow of the air/fuel mixture and burnt gases.These components are operated by the crankshaft and the movement is transmitted via a toothed belt to the camshafts which, in turn, act on the valves. The various components should be perfectly synchronized (TIMED), if this is not the case, the valves could foul against the upper part of the pistons.There are the same number of suitably positioned cams as there are valves to operate; at the front, it is prepared for the fitting of the toothed pulley, through which the motion of the crankshaft is received, by means of a suitably tensioned belt (see ''repair procedures'' section).1, Camshaft oil seal2, Camshaft3, Tappet adjustment shim4, Tapppet5, Cotters6, Upper shim7, Spring8, Oil seal9, Lower shim10, Inlet valve11, Exhaust valve12, Valve guide13, Camshaft pulleyThe camshaft is the component which, through the cams, opens the valves for the required time.Since in 4 stroke engines the working cycle takes place during two revolutions of the crankshaft, whilst the valves have to open only once during the cycle, the camshaft only has to rotate once; therefore, the toothed pulley fitted on the camshaft will have twice the number of teeth as the pulley fitted on the crankshaft.