TM 5-3810-300-24-&P-3
Piston and Piston Rings 1.6
cracks in the piston.
Inspection
Check the cylinder liner and block bore for excessive
If the tin-plate on the piston skirt and the original grooves
out-of-round, taper or high spots which could cause
in the piston rings are intact, it is an indication of very
failure of the piston (refer to Section 1.0 for
little wear.
specifications).
Excessively worn or scored piston skirts, rings or cylinder
Check the tapered fire ring groove width in the current
liners may be an indication of abnormal maintenance or
piston crown with tool J 24599 as shown in Fig. 17.
operating conditions which should be corrected to avoid
Slide the "NO-GO" wire (.106" diameter) of the tool
recurrence of the failure. The use of the correct types
completely around the fire ring groove. Should the wire
and proper maintenance of the lubricating oil filters and
be below flush at any one area, the piston crown must be
air cleaners will reduce to a minimum the amount of
replaced. The "GO" wire (.100"diameter) should be flush
abrasive dust and foreign material introduced into the
or protrude slightly from the fire ring groove.
cylinders and will reduce the rate of wear.
Inspection of the connecting rod, piston pin and piston
Long periods of operation at idle speed and the use of
pin bushing are covered in Section 1.6.1.
improper lubricating oil or fuel must
be avoided,
otherwise a heavy formation of carbon may result and
Other factors that may contribute to piston failure include
cause the rings to stick.
oil leakage into the air box, oil pull-over from the air
cleaner, dribbling injectors, combustion blow-by and low
Keep the lubricating oil and engine coolant at the proper
oil pressure (dilution of the lubricating oil).
levels to prevent overheating of the engine.
Fitting Piston
Examine the piston skirt and crown for score marks,
cracks, damaged ring groove lands or indications of
Measure the piston skirt diameter lengthwise and
overheating. Any piston that has been severely scored
crosswise of the piston pin bore. Measurements should
or overheated must be replaced.
Indications of
be taken at room temperature (70F or 21C). Refer to
overheating or burned spots may be the result of an
Section 1.0 for specifications.
obstruction in the connecting rod oil passage.
Use the magnetic particle inspection methods outlined in
Fig. 18- Measuring Piston-to-Liner clearance
Fig. 17 - Checking Fire Ring Groove in Piston Crown
Section 1.3 under Crankshaft Inspection to check for
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