TM 5-2420-230-24-2
B3.9 and B5.9 Series Engines
Piston Rings (001-047)
Section 1 - Cylinder Block - Group 01
Page 1-87
Inspect the piston rings for the following:
Abrasive wear.
NOTE: Abrasive wear is indicated by concentrated vertical
scratches (B). The chromium plate is worn through and the
face of the ring has a brighter finish compared to the dull
satin finish of a new ring (A).
Abrasive wear can be caused:
1. Ingested abrasive material
2. Inadequate cleaning during a previous repair
3. Particles embedded in the liner.
4. Scuffing and scoring.
NOTE: Scuffing and scoring is indicated by heavy scratches,
metal discoloration, and voids (B).
Scuffing and scoring can be caused by.
1. Engine overheating
2. Oil dilution
3. Improper maintenance of the lubrication system
4. Piston cooling nozzle malfunction.
5. Oil ring plugged by deposits.
NOTE: Scuffing and scoring on the piston rings indicates
a breakdown of the oil film on the cylinder liner wall, caus-
ing transfer of material from the piston ring face to the
cylinder liner.
NOTE: Oil ring plugging is indicated by deposits on the oil
ring grooves (B).
Oil ring plugging can be caused by:
1. Low engine operating temperatures long periods of
idling or a cooling system malfunction
2. Extended oil change intervals
3. Use of the wrong grade of engine oil
4. Use of a poor-quality engine oil.
NOTE: Plugging of the oil ring drains restricts oil drain
back, which floods the piston ring belt area, resulting in a
loss of oil control.
Measure (001-047-010)
Use a new piston ring to measure the clearance in the ring
groove.
Ring Clearance
mm
in
Top
0.075
MIN
0.003
0.150
MAX
0.006
Intermediate
0.085
MIN
0.003
0.150
MAX
0.006
Oil Control
0.040
MIN
0.0016
0.130
MAX
0.0051
L-765
