Operation

Fig. 22 Injection timing advance:

The timing piston is held in its initial position by a preloaded spring. During operation, fuel pressure in the pump cavity is regulated proportional to engine speed by the pressure-control valve and the overflow restriction; as a result, the piston side opposite to the spring is under the same pressure, which increases with increasing engine speed.
When engine speed reaches approximately 300 rpm, fuel pressure reaches a value sufficient to overcome the spring preload and move the timing piston, as shown in Fig. 22, to the left. This axial piston motion is transmitted via the sliding block and pin to the roller ring, which rotates in bearings; this alters the arrangement of cam plate and roller ring so that the rotating cam is lifted at an earlier point in time by the rollers. The rollers with their ring are thus turned by a specific angle relative to cam plate and distributor plunger; this angle can be as much as 12 degrees of camshaft rotation or 24 crankshaft degrees.