Introduction - TIMING SYSTEM

1.1, 1.2 8v

A 'spheroid cast iron' overhead camshaft operated by a timing belt.

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 seal

2, Camshaft

3, Tappet adjustment shim

4, Tapppet

5, Cotters

6, Upper shim

7, Spring

8, Oil seal

9, Lower shim

10, Inlet valve

11, Exhaust valve

12, Valve guide

The 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.