Enlarged or distorted spray holes:
holes. Wires may be used if a smaller size wire is
Caused by cleaning with drills or other instruments.
used than the spray hole.
(b) Inspect cup for plunger seat pattern. If
(4) A clean shop, clean tools and good
plunger seat covers 40 per cent continuous area around
cleaning practices are essential to good injector repair.
cup cone or plunger bore, it is possible cup may be
Most injector failures occur because of dirt. Clean all
parts before assembly:
Caution: Never alter size of injector cup
(2) Injector body.
(a) Inspect injector body plunger bore for
scoring. If scores are not too deep, injector body should
be honed and fitted with an oversized plunger.
(b) Use a strong magnifying glass to check
for burs, carbon and distorted radii in orifices. When
injector orifices are damaged, the injector will not
function properly. Do not attempt cleaning with , wires,
plug gages, etc; use solvent cleaners.
(c) Check injector inlet and drain connection
holes for mutilation to threads and copper gasket
surface, if multilated mark for repair.
Figure 3-74. Injector removal.
(3) Injector plunger.
(a) Check closely for metal seizure. As a
rule this is the only true indication of scuffing or scoring.
(b) Bright spots or surface disruption at top
of plunger, on opposite side at bottom of plunger or at
mid-point, usually are normal results of rocker lever
thrust action. Unless metal is displaced or wear is
measurable at these points, the plunger may be reused.
If worn excessively install a new plunger.
Figure 3-75. Injector in ST-569 holding fixture.
Figure 3-76. New injector cup tip.
(c) Narrow streaks running the length of the
(1) Injector cup.
plunger usually are the result of the varying thickness of
(a) Inspect injector spray holes and tip with
penetrate treatment used to prevent rusting and the
magnifying glass. Compare with new cup shown in
plunger is satisfactory for reuse unless a surface
disruption is evident.
(4) Injector spring.
1. Abrasive wear: This wear can begin
(a) Check spring for excessive wear or
internally; therefore, inspect both interior and exterior,
(b) Test spring tension on spring tester,
Corrosion damage and effect of
excessive heat: This condition usually results from high
acid or sulpher content in fuel or overload operating