Usage:
793 (3SJ),
793B (1HL),
793C (4AR) Off-Highway Trucks
Description of Change: Three changes have been made to the high pressure turbocharger groups on the engines in these trucks. Changes were made to the compressor housing, thrust bearing, and compressor seal. These three changes combine to improve the service life and reliability of the high pressure turbochargers on the above trucks.
Compressor Housing
The 793, 793B, and 793C turbochargers are now made with a cast iron compressor housing with improved resistance to warping caused by heat. The absence of the warping makes it easier to remove and install the compressor housing on the cartridge. Also, the warping of the former aluminum compressor housing could allow the compressor wheel to rub part of the compressor housing. The cast iron compressor housing will also better resist wear and erosion caused by relative movement between the compressor housing and the air pipe. This will help prevent boost leaks. The new cast iron compressor housing bolts to the bearing housing. The former aluminum compressor housing clamped onto the bearing housing.
Thrust Bearing
The 793 and 793B turbocharger thrust bearing changed to a single piece bonded design. The bonded thrust bearing does not use rivets to attach to the back plate. The former thrust bearing used rivets to attach to the back plate. These rivets would sometimes become loose. The 793C turbocharger has had this single piece bonded design since first production.
Compressor Seal
The new turbocharger and cartridge groups contain a dynamic compressor seal with a wear stop. This will improve the service life of the 793, 793B, and 793C turbochargers.
Adaptable To: This section is divided into two parts. First are the changes that are adaptable to 793 and 793B Off-Highway Trucks. Second are the changes that are adaptable to 793C Off-Highway Trucks.
793 And 793B Off-Highway Trucks
Charts A and B provide lists of the improved serviceable parts that are adaptable to the high pressure turbochargers in the 108-5559 (793) and 9Y-8911 (793B) Turbocharger Groups.
The new high pressure turbocharger group and major parts are all serviceable and can be ordered through the Caterpillar part system. The new cast iron compressor housing can not be used with the former cartridge groups.
This is because the new cast iron compressor housing bolts to the cartridge group, while the former compressor housing clamps on the former cartridge group.
To provide clearance for the new compressor housing, different adapters are needed for the turbocharger oil and cooling lines. Due to the need for additional clearance, bolts with low profile heads should be used to attach the new compressor housing to the new cartridge group. Chart C lists the parts needed to install a new compressor housing and new cartridge group.
NOTE: Some early 138-2292 Turbocharger Groups were shipped with the 125-5325 Bolts attaching the cast iron compressor housing to the cartridge. These bolts should be replaced with 147-3737 Bolts prior to installation of the turbocharger group on the engine.
These improvements are effective with Remanufactured 3516 Electronic Unit Injected (7CL394, 399 - Up) Engine for use in 793B Off-Highway Trucks.
793C Off-Highway Trucks
Charts D and E provide lists of the improved serviceable parts that are adaptable to the high pressure turbochargers in the 121-5802 Turbocharger Group.
NOTE: Both the new 138-2305 and former 134-0386 Turbocharger Groups include the new style single piece bonded design thrust bearing. This prevents looseness with the back plate.
These improvements are effective with the 3516B (7TR) Engines in 793C (4AR155) Off-Highway Trucks.
