HOUSING AS-FRONT 1260102 - Caterpillar

All 3408B And 3412 EnginesDescription of Change: A new timing gear housing, nut and washer are used in the front housing groups on 3408B and 3412 Engines. Formerly, relative movement between the front housing group and the cylinder block could be induced by the fan drive, water pump, or other driven components bolted to the timing gear housing. The relative movement could cause the gasket between the housing and cylinder block to be worn away. This could allow oil to leak between the housing and cylinder block. The new timing gear housing has one additional mounting hole. See Illustration 1. The new mounting hole coincides with a new stud in the cylinder block groups. See Illustration 2. The additional mounting hole along with the new stud, washer, and nut will allow the front housing groups to be held more securely on the front of the cylinder block. This will eliminate relative movement between the front housing group and cylinder block which will help prevent oil leaks between the front housing group and the cylinder block.Adaptable As: The new 7C4843 Timing Gear Housing, 1D4717 Nut and 5M2894 Washer are in effect with the front housing groups on 3408B and 3412 Engines as shown in Chart A. The new 7C7407 Stud is in effect with the cylinder block groups on 3408B and 3412 Engines as shown in Chart B. The new 7C4843 Timing Gear Housing, 1D4717 Nut, 5M2894 Washer, and 7C7407 Stud are adaptable to all earlier 3408B and 3412 Engines. On earlier engines, a 1/8" pipe plug is located where the new 7C7407 Stud is installed. See Illustration 2. Remove the plug and install the end of the stud with 1/8" pipe threads in the hole in the cylinder block.
Illustration 1. Location of the new hole in the timing gear housing.
Illustration 2. Location of the new 7C7407 Stud in the cylinder block. The additional hole can be added to earlier timing gear housings as shown in Illustration 1. The timing gear housing must be removed so that the 1/8" pipe plug can be removed from the cylinder block, where the 7C7407 Stud is to be installed. See Illustration 2.
An additional fastener can be added to earlier timing gear housings and cylinder blocks without removing the timing gear cover. Add the additional mounting hole to the timing gear housing at the location shown in Illustration 3. Then counterbore the housing and drill and tap the cylinder block as shown in Illustration 4. Use a S1588 Bolt and a 5M2894 Washer to fasten the housing to the block.
Illustration 3. Location of additional mounting hole in the timing gear housing.
Illustration 4. Dimensions for hole in cylinder block and counterbore in housing.