ENGINEMAN 1 & C
and the manufacturer. The following brief
description of the procedures for equipment made
by two different manufacturers emphasizes some
of these similarities, and further emphasizes the
need for following only the procedures indicated
in the appropriate manufacturers technical
A plunger of a Bosch fuel injection pump can
be loosened by cleaning. However, if the plunger
does not slide freely in the barrel, both the plunger
and barrel should be cleaned with an approved
cleaning fluid, rinsed in clean fuel oil, and blown
dry with compressed air. A small quantity of mut-
ton tallow should then be placed on the plunger.
Working the plunger back and forth and rotating
it in the barrel should remove all gummy deposits.
Instructions for Bosch fuel injection equipment
state that such items as hard or sharp tools or
abrasives of any kind should never be used in
cleaning the pumps.
Freeing the sticking plunger in a GM unit in-
jector may be done in much the same manner as
in a Bosch pump.
Stains on plungers may be removed by the use
of a limited quantity of jewelers rouge on a piece
of soft tissue paper. It is important to remember
that the plunger should not be lapped to the
bushing with an abrasive such as jewelers rouge.
After a plunger has been cleaned with jewelers
rouge, it must be cleaned thoroughly with diesel
fuel before being placed in the bushing. If after
repeated cleanings, the plunger still does not slide
freely, you may assume that either the plunger or
the bushing is distorted.
The principal difference in the cleaning pro-
cedures for these two units of equipment is in the
use of abrasives. If the recommended cleaning
procedure for these units fails to loosen the
plunger so it will slide freely, the plunger and its
mating part will have to be replaced.
Broken Plunger Spring
A pump of an injector will fail when the
plunger spring breaks and fails to return the
plunger after injection has occurred.
Factors which contribute to broken plunger
failure to inspect the springs
thoroughly and careless handling.
Broken plunger springs must be replaced. Also
they should be replaced when there is evidence of
cracking, chipping, nicking, weakening of the
spring, excessive wear, or when the condition of
the spring is doubtful.
Jammed Fuel Control Rack
If an engine is to operate satisfactorily, the fuel
control rack must be completely free to move.
Since the rack controls the quantity of fuel
injected per stroke, any resistance to motion will
result in governing difficulties. When this occurs,
the engine speed may fluctuate (decreasing as the
engine is loaded; racing as the load is removed),
or the engine may hunt continuously or only when
the load is changed. If the fuel control rack
becomes jammed, it may become impossible to
control the engine speed with the throttle. The
engine may even resist securing efforts under such
conditions. Since a sticking fuel control rack can
cause serious difficulty, especially in an emer-
gency, every effort should be made to prevent its
occurrence. The best way to check for a sticking
fuel control rack is to disconnect the linkage to
the governor and attempt to move the rack by
hand. There should be no resistance to movement
of the rack when all springs and linkages are
A fuel control rack may stick or jam as a result
of a stuck plunger, dirt or paint in the rack
mechanism, a damaged rack or gear, or improper
assembly. When this jamming or sticking occurs,
it is necessary to determine the cause of binding.
If it is due to damage, the damaged parts must
be replaced; if the stickiness is due to the presence
of dirt, a thorough cleaning of all parts will prob-
ably correct the trouble. Avoid errors in
reassembly and adjustment by carefully studying
Backlash in the Control Rack
Backlash, looseness, or play in the fuel con-
trol rack, like sticking or binding of the rack, will
influence governing of the engine. Proper
governing is based on the theory that for every
change in speed of the engine, there will be a cor-
responding change in the quantity of fuel injected.