Isuzu L Series Manual page 7

II. Engine Component Description
Pump Timing
This drawing shows the relationship between cam lift and cam angle when pre-stroke length is
changed. The stroke length represented as "L" is always constant. When the pumps are advanced
by using a thinner shim, the timing sleeve is lowered and the start of injection occurs at the
beginning of the cam lift. (Note: the sleeve is fixed to the pump housing.)
Conversely, when the pump is retarded by using a thicker shim, the pre-stroke is lengthened
because the timing sleeve is raised. Raising the pump housing changes the start of injection to the
last half of the cam lift. It also reduces the total number of cam degrees to complete one injection.
Rack Operation
U
L-Series Diesel
The plunger's roller follower rides directly
on the cam lobe. Plunger position is
controlled by cam lobe lift. Rack movement
rotates the sleeve, changing the spill port
position relative to the plunger's helix. This,
in turn, varies the amount of fuel injected.
NOTE: In order to remove the pumps from
the block, the rack slide must be centered
otherwise the pumps will hang-up on the
cylinder block casting.
6