TM 5-3895-346-14
ENGINE OVERHAUL
SHOP NOTES
Figure 2. Refinishing Lapping Blocks
Alternate the blocks from time to time. For example, assuming the blocks are numbered 1, 2, and 3, work 1
and 2 together, then 1 and 3, and finish by working 2 and 3 together. Continue this procedure until all of the
blocks are perfectly flat and free of imperfections
Imperfections are evident when the blocks are clean and held under a strong light. The blocks are satisfactory
when the entire surface is a solid dark grey. Bright or exceptionally dark spots indicate defects and additional
lapping is required.
After the surfaces have been finished, remove the powder by rinsing the lapping blocks in trichloroethylene and
scrubbing with a bristle brush.
When not in use, protect the lapping blocks against damage and dust by storing them in a close-fitting wooden
container.
EFFECT OF PREIGNITION ON FUEL INJECTOR
Preignition is due to ignition of fuel or lubricating oil in the combustion chamber before the normal injection
period. The piston compresses the burning mixture to excessive temperatures and pressures and may
eventually cause burning of the injector spray tip, leading to failure of the injectors in other cylinders.
When preignition occurs, remove all of the injectors and check for burned spray tips or enlarged spray tip
orifices.
Before replacing the injectors, check the engine for the cause of preignition to avoid recurrence of the problem.
Check for oil pullover from the oil bath air cleaner, damaged blower housing gasket, defective blower oil seals,
high crankcase pressure, plugged air box drains, ineffective oil control rings or dilution of the lubricating
oil.
INJECTOR TIMING
If it is suspected that a fuel injector is "out of time", the injector rack-to- gear timing may be checked without
disassembling the injector.
A hole located in the injector body, on the side opposite the identification tag, may be used to visually
determine whether or not the injector rack and gear are correctly timed. When the rack is all the way in (full-
fuel position), the flat side of the plunger will be visible in the hole, indicating that the injector is "in time". If the
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