Visual Inspection of Plunger

TM 10-3930-634-34

(h) If the valve opening pressure is below 2300

and ending of injection should be sharp and the fuel in-

psi or atomization is poor, replace the needle valve and

jected should be finely atomized.

tip assembly.

(b) If all of the spray tip orifices are not, open

(i) If the valve opening pressure is within 2300

and injecting evenly, clean the orifices during injector

to 3300 psi proceed to check for spray tip seat leakage.

over-haul.

Pump up the injector and maintain a pressure of 1500

(6) Visual Inspection of Plunger.

psi for 15 seconds by actuating pump handle. Inspect

(a) An injector which passes the previous above

the spray tip seat for leakage. There should be no fuel

tests must have the plunger checked visually, under a

droplets although a slight wetting of the end of the

magnifying glass, for excessive wear or for a possible

valve tip is permissible.

chip in the bottom helix. There is a small area on the

(j) Check the needle valve lift (fig. 3-37) as

bottom helix and lower portion of the upper helix, that

follows:

if chipped, will not be indicated in any of the tests.

1. Zero the indicator by placing the bottom

(b) Remove the plunger from the injector as fol-

surface of the plunger assembly on a flat surface and

lows:

zero the indicator dial.

1. Support the injector, right side up, in the

2. Place the spray tip and needle valve assem-

holding fixture (fig. 3-35) or in injector vise jaws.

bly tight against the bottom of the gage with the quill

2. Compress the follower spring; then using a

of the needle valve in the hole in the plunger.

screwdriver, raise the spring above the stop pin and re-

3. While holding the spray tip and needle

move the pin (fig. 3-35). Release the spring gradually.

valve assembly tight against the gage, read the needle

3. Lift the follower and plunger from the in-

valve lift on the indicator. This lift should be 0.008 to

jector body as an assembly.

0.018 inch; if it exceeds 0.018 inch, the tip assembly

4. Inspect the plunger (fig. 3-36) for chipped

must be replaced. If the lift is less than 0.008 inch, in-

edges. If plunger is chipped, replace the plunger and

spect for foreign material between the needle valve

bushing assembly.

and tip seat.

5. If the plunger is in good condition, reinstall

4. If the needle valve lift is within the limits,

the plunger and follower.

install a new needle valve spring and recheck the valve

(7) Needle Valve Test.

opening pressure and valve action. Low valve opening

(a) Remove injector nut and remove all the

pressure or poor atomization with a new spring indi-

valve parts below the injector bushing as outlined be-

cates the spray tip and needle valve assembly is defec-

low.

tive and must be replaced.

(b) Clean all the carbon off the spray tip seats in

(k) Reassemble the injector.

the injector nut as outlined below.

(8) Fuel Output Test.

(c) If the spray pattern test indicated that tip

(a) When injectors are removed from an engine

cleaning is necessary, clean the carbon from the tip

for output testing, and if satisfactory, reinstalled with-

cavity below the needle valve and orifices as outlined

out disassembly, extreme care must be taken to avoid

below.

reversing the fuel flow. Note the direction of fuel flow

(d) With the injector nut and spray tip cleaned,

through the injector before removal from the engine.

clamp the nonthreaded end of the body in a bench vise.

When the fuel flow is reversed, dirt trapped by the fil-

Then, assemble the check valve, check valve cage,

ter element is back-flushed into the injector compo-

spring, spring seat, spring cage, needle valve and tip

nents. To avoid reversing the fuel flow when checking

assembly on top of the body. Carefully pilot the injec-

injector fuel output on the comparator use the appro-

tor nut over the spray tip and valve parts and thread it

priate adapter. The position of the fuel flow pipes illus-

on the injector body. Tighten the injector nut to 75-85

trated in figure 3-38 depends on the adapter being

lb-ft torque.

used and the direction of fuel flow through the injec-

(e) Remove the body with the injector parts

tors.

from the bench vise and install in the adapter in the in-

jector tester as illustrated in figure 3-34,

NOTE

(f) Operate the pump handle until the spray tip

The fuel passages in some adapters are drilled

valve has opened several times to purge the air from

straight through the adapters while others

the system.

are cross drilled.

(g) Operate the pump handle with smooth even

(b) Install and operate the injector in the com-

strokes (40 strokes per minute) and note the pressure

parator and check the fuel output as follows:

at which the needle valve opens. The valve should open

1. Place the injector in the comparator, as il-

between 2300 and 3300 psi. The opening and closing

lustrated in figure 3-39. Then, turn the wheel to

action should be sharp and produce a finely atomized

spray.

clamp the injector and adapter in position.

3-28