3.9.
Fan-belt Pulley Attachment
The fan-belt pulley transmits power from the
crankshaft to the various auxiliary components
such as the water-pump, generator, power steer-
ing and brake-fluid pump, and the cooling fan
itself. The pulley contains a wheel which guides
and supports the fan belt and the hub. The first
main journal of the crankshaft has axial rectan-
gular keyway slot(s) on an extended parallel portion of slightly smaller diameter. The bores of
the timing gear (which, drives the camshaft) and the pulley hub have internal slots and form a
transition push fit with the shaft. However the driving torque is transferred from the shaft to
the gear and pulley through the Woodruff key(s) (Figs. 3.69 and 3.70). To prevent loosening of
the components due to vibration, a large set-bolt is screwed into the end of crankshaft to clamp
the assembly together.
Fig. 3.69. Fan-belt pulley and oil-seal assembly. Fig- 3.70. Crankshaft pulley, timing sprocket, and oil-seal assembly.
The belt generally has trapezium cross-section to match the tapered sides of the pulley-
wheel circumferential groove. The factional grip of the belt transmits the drive which is
reinforced by the wedge action of the tapered contact surfaces. Belts are mostly made from
composite fabrics of rubber and nylon or terylene. The life-span of the belt depends upon the
accurate alignment of the pulley-wheel system and the correct tension in the belt.
