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 18 of 836
TM 9-2320-272-24-4
5-3. CYLINDER HEAD REPAIR (Contd)
28.
Inspect valve crossheads (1) in accordance with instructions in para. 2-15. Discard crossheads (1) if
defective.
a. Check valve crossheads (1) for damaged adjusting screw threads (5) and excessive wear on rocker
lever contact area (2).
b. Using micrometer, set small bore gauge at 0.4402 in. (11.181 mm).
c. Attempt to insert gauge into bore (4). Discard valve crosshead (1) if bore gauge goes into bore (4).
d. Check for out-of-round bore (4) by gauging at several points 90° apart. Discard valve crosshead (1)
if bore (4) is out of round.
e. Check valve stem counterbore depth (3). Discard crosshead (1) if depth (3) is not 0.1200-0.1400 in.
(3.048-3.556 mm).
29.
Inspect eight valve guides (9) in accordance with instructions in para. 2-15. If defective, mark valve
guides (9) for replacement.
a. Check eight valve guides (9) for chips, cracks, burrs, or broken out sections. If chipped, cracked,
broken, or burrs are found, mark for replacement.
b. Check valve guide (9) for protrusion (7). If protrusion (7) is not 1.270-1.280 in. (32.26-32.51 mm)
above cylinder head surface (8), mark valve guide (9) for replacement.
c. Set small bore gauge at 0.4552 in. (11.562 mm) and attempt to insert gauge into guide bore (6). If
gauge goes into bore (6), mark guide (9) for replacement.
30.
Check valve head (14) and intake and exhaust valves (15) for cracks, warping, pits, burns, or
cupping. Discard valve(s) (15) if cracked or warped, pitted, burned, or cupped.
a. Check rim thickness (13) on intake and exhaust valves (15). Discard valve (15) if rim thickness (13)
is less than 0.105 in. (2.67 mm).
b. Check intake and exhaust valve keeper grooves (11) for wear. Use new keeper to check grooves (11).
Discard valve(s) (15) if new keepers fit loosely in grooves (11).
c. Check valve stem (12) for cracks, scoring, and galling. If cracked, scored, or galled, discard valve (15).
d. Measure valve stem (10) outside diameter with micrometer. If stem (10) outside diameter is less
than 0.449 in. (11.41 mm), discard valve (15).
CAUTION
Use care when selecting replacement valve springs. Intermixing of
old and new valve guides in any one cylinder head is permissible
only if a specific crosshead has two of the same type or equivalent
guides and springs installed under it.
31.
Inspect valve springs (16) in accordance with instructions in para. 2-15. Discard valve springs (16) if
defective.
a. Check valve springs (16) for distortions, cracked, or collapsed coils. Discard valve spring (16) if
distorted, or if coils are cracked or collapsed.
b. Check valve spring (16) free length. No. 1 valve spring is 2.29 in. (58 mm) in length. No 2. valve
spring is 2.69 in. (68 mm) in length.
c. Using spring tester, inspect for serviceability by checking load when spring is compressed.
Discard spring No. 1 if spring does not give load of at least 150 lb (667 N) when compressed to
1.77 in (45 mm). Discard spring No. 2 if spring does not give load of at least 143 lb (636 N) when
compressed to 1.72 in. (44 mm).
5-12
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