TM-9-2320-272-24-4
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 4 OF 4
JUNE 1998
TM-9-2320-272-24-4 - Page 206 of 836
TM 9-2320-272-24-4
5-29. CRANKSHAFT AND GEAR MAINTENANCE (Contd)
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Inspect connecting rod caps (14) for cracks, breaks, and pits. Replace connecting rod caps (14) if
cracked, broken, or pitted.
Inspect main bearing caps (7) for cracks, breaks, and pits. Replace main bearing caps (7) if cracked,
broken, or pitted.
Inspect engine block (9) for scratches, grooves, wear, and stripped threads. Replace or repair if
engine block (9) is scratched, grooved, worn, or threads are stripped.
Measure outside diameter of main bearing journals (2) for out-of-roundness across points A and B.
Replace crankshaft (1) if difference of measurements exceeds 0.002 in. (0.0051 mm).
Measure outside diameter of main bearing journals (2) for taper at points C and D. Replace
crankshaft (1) if difference of measurements exceeds 0.0005 in. (0.013 mm).
Measure outside diameter of connecting rod journals (3) for out-of-roundness across points A and B.
Replace crankshaft (1) if difference of measurements exceeds 0.002 in. (0.0050 mm).
Measure outside diameter of connecting rod journals (3) for taper at points C and D. Replace
crankshaft (1) if difference of measurements exceeds 0.0005 in. (0.0127 mm).
Inspect front (4) and rear (5) crankshaft seal wear surfaces for scratches and grooves. Replace
crankshaft (1) if scratched or grooved.
CAUTION
Ensure main bearings are installed in proper mating seats.
Failure to do so will cause engine to fail.
Install new thrust bearing (8) in No. 4 main bearing seat (11).
Install six new upper main bearings (7) in main bearing seats (10). Ensure tangs (12) of upper main
bearings (7) are aligned with slots (13) of main bearings seats (10).
Install crankshaft (1) in engine block (9).
Install seven new lower main bearings (6) in main bearing caps (7).
Place plastic strips across width of seven main bearing journals (2).
5-200
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