ARMY TM 9-2815-259-24
AIR FORCE TO 38G1-125-2
MARINE CORPS 09249A/09246A-24
5.4.2. IDLER GEARS AND IDLER GEAR SHAFTS.
The following procedures require complete access to the engine. If
necessary, remove engine from generator set, refer to TM 9-6115-671-14.
Mount engine on repair stand (NSN 4910-01-016-1835 or equal) as outlined
in paragraph 4.10.
a. Idler Gear End Play and Backlash Test.
Remove timing gear cover, refer to paragraph 4.9.2.
Remove oil pan, refer to paragraph 4.5.3.
Measure idler gear end play as follows:
Using dial caliper, check end play of upper and lower idler gears. Refer to Table 5-4 for
Observe specifications for new end play and maximum acceptable end play.
Measure idler timing gear backlash as follows:
Using a dial indicator, measure backlash between timing gears. Refer to Table 5-4 for
Measure upper idler gear-to-camshaft gear. Refer to Table 5-4.
Measure upper idler gear-to-injection pump gear. Refer to Table 5-4.
Measure upper idler-to-crankshaft gear. Refer to Table 5-4.
Measure lower idler gear-to-crankshaft. Refer to Table 5-4.
Measure lower idler gear-to-oil pump gear. Refer to Table 5-4.
If backlash is not within specification, install new timing gears.
Table 5-4. Camshaft and Timing Gear Train Specifications
Upper Idler Shaft OD
2.7463 - 2.7471 in. (69.757 - 69.777 mm)
Upper Idler Gear Bushing ID
2.7481 - 2.7493 in. (69.802 - 69.832 mm)
Lower Idler Shaft OD
1.7495 - 1.7505 in. (44.437 - 44.463 mm)
Lower Idler Gear Bushing ID
1.7515 - 1.7535 in. (44.489 - 44.539 mm)
Upper and Lower Idler Gear End Play
0.0037 - 0.0057 in. (0.095 - 0.145 mm)