HOUSING ASSEM. 2P8695 - Caterpillar

--------------- END SUPPLEMENT ---------------Description of Change: New diverter valve groups and a new plunger assembly are used in the hydramechanical shut off (HMSO) group on the above engines. The new diverter valve groups have a latch design which holds the fuel rack in the "shut off" position. To release the rack the low oil pressure override actuator must be pushed. Also, several diverter valve groups are now available for different applications.
Formerly, a check valve was used along with the diverter valve group to prevent the loss of oil pressure in the rack circuit when the rack moved to the "shut off" position. Also, with the former diverter valve group the fuel rack was automatically released when the engine RPM had decreased below the overspeed set point. During an oil pressure failure, it was possible for the engine to cycle from high to low RPM.
The new bypass valve plunger assembly is flat on the end to give a large area to seal against. The former plunger assembly had a tapered end a smaller area for a seal.
There have also been some failures of the drive splines in the HMSO group. Most of these failures have been caused by not enough lubrication. Changes have been made to permit pressure lubrication to the spline area. The top of the engine oil pump must be filled with two liters (quarts) of engine oil before start-up if the HMSO oil sump has been drained. The fitting in the illustration must be removed and the two liters (quarts) oil may be added.
Adaptable As: The new diverter valve groups and their applications are shown in Chart A. The new valve groups are in effect with the serial numbers shown in Chart B. The former diverter valve is still available for earlier engines. The new 5N9063 Plunger Assembly is a direct replacement for the former 8M874 Plunger Assembly in this application.
The new plunger assembly is in effect with the serial numbers shown in Chart C.
Illustration 1. Location of fitting in oil pump.