TM-9-2320-272-24-3
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 3 OF 4
JUNE 1998
TM-9-2320-272-24-3 - Page 56 of 799
TM 9-2320-272-24-3
4-52. AIR COMPRESSOR MAINTENANCE (Contd)
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Place new intermediate compression ring (3) in groove of piston (1). Using feeler gauge, measure
distance between groove wall and intermediate compression ring (3). If distance exceeds 0.0045 in.
(0.114 mm), replace piston (1).
Place new top compression ring (2) in groove of piston (1). Using feeler gauge, measure distance
between groove wall and top compression ring (2). If distance exceeds 0.0045 in. (0.114 mm), replace
piston (1).
Inspect compressor crankcase (4) for scoring, breaks, and wear. If scored, broken, or worn, replace
compressor crankcase (4).
Measure inside diameter of piston bore (5) at two places, 1 in. (25.4 mm) below compressor head
surface (6) of compressor crankcase (4). If inside diameter exceeds 3.629 in. (92.18 mm), replace
compressor crankcase (4).
Subtract two bore diameter measurements. If difference of diameters exceed 0.002 in. (0.05 mm),
replace compressor crankcase (4).
Inspect compressor crankcase bushing (8) for nicks, scoring, and wear. Measure inside diameter of
bushing (8). If nicked, scored or inside diameter exceeds 1.878 in. (47.70 mm), replace compressor
crankcase bushing (8).
Perform steps 19 through 22 bushing requires replacement.
Support compressor crankcase (4) on arbor press with bushing bore (7) facing up.
Press bushing (8) from bushing bore (7). Discard bushing (8).
Lubricate new bushing (8) with clean engine oil.
Using arbor press, install new bushing (8) in bushing bore (7) until flush with bore surface.
4-320
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