0398072 JOHNSON CARB ASSY., Lower

Do not operate or work on this product unless you have read and understood the instruction and warnings in the relevant Operation and Maintenance Manuals and relevant service literature. Failure to follow the instructions or heed the warnings could result in injury or death. Proper care is your responsibility.
The new rear accessory drive is adaptable back to first production. Groups included in the new rear accessory drive are listed in Table 1.Replacement or modification of the existing flywheel housing is required for the upgrade to the new spur gear drive system. If modifying an existing housing, follow the instructions listed in Step 2 of the "Rework Procedure".The new accessory drive is effective with the following serial numbers:
FDB01752 for low altitude engine arrangements ( 235-0300 Engine Ar)
FDB01749 for high altitude engine arrangements ( 235-0280 Engine Ar)The new accessory drive is effective for the engine serial numbers S/N:8WM03134-UP.
Table 1
New Part Number Former Part Number
387-2879 Accessory Drive Gp 350-1830 Accessory Drive Gp
398-3070 Flywheel Housing Gp 317-7596 Flywheel Housing Gp
386-2937 Rear Gear Gp 121-5720 Rear Gear Gp
Table 2
Required Parts
Qty Part Number
1 442-2324 Gear Shaft
2 443-6069 Idler Gear As
2 156-9744 Camshaft Drive Gear
1 382-1828 Auxiliary Drive Gear
1 443-9634 Idler Gear As
1 386-3188 Cluster Gear Assembly
1 390-0481 Shaft As
1 397-9308 Idler Shaft
1 398-3068 Flywheel Housing (1)
or
461-9988 Flywheel Housing (1)
1 399-7361 Crankshaft Gear
(1) This housing is required only if the existing flywheel housing is not being modified.Rework Procedure
Reference: Disassembly and Assembly, SENR1126, "3500 and 3500B High Displacement Engines for Caterpillar Built Machines" Disassembly and Assembly, RENR8334, "793D Off-Highway Truck"Note: Installation of the new accessory drive is best performed with the engine out of the truck chassis.
Remove the following parts after removing the engine from the truck chassis:
Flywheel
Flywheel housing
Accessory drive
Rear gear group
Illustration 1 g03337671
Modify the existing housing by creating clearance for the new spur gear system in four areas. The areas requiring clearance are the camshaft drive port, the accessory drive port, the crankshaft gear port, and the material between the crankshaft gear port and the idler cluster gear port.If using a 398-3068 Flywheel Housing or a new 461-9988 Flywheel Housing, proceed to Step 3.
Illustration 2 g03299837
View of detail A, the camshaft drive port.
(A) BossNote: Some flywheel housings will not be affected by boss (A)
Create a clearance of 262.9 0.5 mm (10.4 0.02 inch) concentric with the camshaft. Refer to Illustration 2.
Illustration 3 g03299838
View of detail B, the accessory drive port.
Create a clearance of 265 0.5 mm (10.4 0.02 inch) concentric with the accessory drive pilot hole to the accessory drive shaft hole. Refer to Illustration 3.
Illustration 4 g03299839
View of detail C, the crankshaft gear port.
Reduce the outside diameter (OD) of the flywheel housing lip by 2.6 0.5 mm (0.10 0.02 inch) Refer to Illustration 4.
Illustration 5 g03337568
Measuring for clearance
Measure the distance between the opening of the crankshaft gear port and the cast shoulder that encircles the port. Measure at a location nearest to the idler cluster gear port. The maximum acceptable distance is 28.3 0.1 mm (1.114 0.004 inch).
Illustration 6 g03337576
View of detail D
(E) 28.3 0.1 mm (1.114 0.004