TM 5-3895-359-14&P
Examine the piston skirt and crown for score marks,
The bearing must be installed before
cracks, damaged ring groove lands or indications of
assembling the piston skirt and
overheating. Any piston that has been severely scored
crown.
or overheated must be replaced.
Indications of
2. Lubricate the metal seal ring (Fig. 6) with engine oil
overheating or burned spots may be the result of an
and install it with the chamfer or counterbore directed
obstruction in the connecting rod oil passage.
toward the bottom of the piston.
NOTE
Check the tapered fire ring groove width in the current
The current seal rings are made of
piston crown with tool J 24599 as shown in Fig. 5 Slide
cast iron and are identified by the tin-
the "NO-GO" wire (.106" diameter) of the tool
plating on the outside diameter, a
completely around the fire ring groove. Should the wire
black oxide finish, or a dull cast iron
be below flush at any one area, the piston crown must
color. These rings can be mixed in
be replaced. The "GO" wire (.100" diameter) should be
an engine. The former steel ring,
flush or protrude slightly from the fire ring groove.
identified
by
a
very
shiny
appearance, must not be used for
Check the cylinder liner and block bore for excessive
service.
out-of-round, taper or high spots which could cause
3. Compress the seal ring with ring compressor J 23453
failure of the piston (refer to Page 10-2-133 for
and push the skirt into position on the piston crown.
specifications.)
NOTE
Before completely assembling the
Inspection of the connecting rod, piston pin and piston
piston, check to make sure the seal
pin bushing are covered on Page 10-2-86.
ring does not stick in the ring
groove.
It is imperative for
Other factors that may contribute to piston failure
satisfactory engine operation that the
include oil leakage into the air box, oil pull-over from the
seal ring is free in the piston crown
air cleaner, dribbling injectors, combustion blow-by and
groove.
Check the full 360
low oil pressure (dilution of the lubricating oil).
circumference of the groove to be
sure there are no tight spots. When
the piston crown, seal ring and
piston skirt are assembled, the skirt
should spin freely on the crown
(crown top down on the bench). If
the seal ring sticks, remove high
spots or nicks in the groove with a
flat file. If this does not relieve
sticking, replace the piston crown.
Fig. 7. Installing Piston Pin
Assemble Piston
1. Install the bearing (bushing) in the piston crown. It
should slide into the piston crown without force. With
Fig. 8. Tightening Connecting Rod to Piston Pin
new parts, there is .0005" to .0105" clearance between
Bolts
the edge of the bushing and the groove in the piston
crown.
NOTE
10-2-81
