cylinder. Low pressure and high temperature indicate late timing; high pressure and high temperature
indicate the injection of too much fuel.
The amount of fuel being injected is checked in the following way: intake and exhaust valves are
closed and a swanneck pipe is installed in the place of the pump's delivery pipe and valve. Move the
pump rack bar to full-load position and bar the engine around until the fuel stops flowing through the
swanneck pipe. The pump is then ready to be tested. Delivery from each pump element is led off to a
set of test nozzles which discharge into measuring cylinders. In this way, the discharge from each pump
can be measured under working conditions.
a. Fuel flow. To measure the flow of fuel, the number of pump strokes must be known as well
as the quantity of fuel for the desired position. A counter measures the number of strokes in either the
forward or reverse direction and an adjusting screw indicates the position of the fuel rack. The adjusting
screw is mounted in a sleeve which is notched in such a manner that the fixed position of the rack--idle,
full fuel, and off--is maintained in the proper relationship. After one of these positions is adjusted, the
screw is locked to the sleeve and the sleeve and screw then move as a unit known as the control sleeve
unit. Other parts of the equipment provide for proper support, filtering, and return of fuel oil. Filtered
fuel is delivered to the injection pump through a flexible hose; relatively constant fuel pressure, 35-40
psi, is maintained by a pressure relief valve. Fuel bypassed by the relief valve is returned to the fuel
storage tank.
b. Other checks. After making sure that the injector nozzles are working properly (par. 2.11),
check the fuel pump discharge valve and spring assembly. If load speed, timing, and water jacket
temperature remain constant, compression and cylinder pressures and exhaust temperatures normally
remain constant. Check the fuel pump timing adjustment; if it is not correct, adjust the thickness of the
shims to raise or lower the position of pump suction support for the individual pump.
2.11.
INJECTION NOZZLES
If defective, an injector nozzle can cause cylinder knock, overheating of the engine, dirty exhaust,
and increased fuel consumption with loss of power. Tightness of all the nuts on the injector should be
checked since a leakage at this point may prevent injection and allow fuel to drain into the crankcase
lubricating oil.
60
Previous Page
