COVER-FUEL PUMP GEAR 9N5576 - Caterpillar

Industrial Engines:
3508 (S/N: 95Y1-UP; 68Z1-UP)
3512 (S/N: 49Y1-UP; 65Z1-UP)
3516 (S/N: 27Z1-UP; 71Z1-UP)
Generator Set Engines:
3508 (S/N: 23Z1-UP; 70Z1-UP)
3512 (S/N: 24Z1-UP; 67Z1-UP)
3516 (S/N: 73Z1-UP)
Marine Engines:
3508 (S/N: 96Y1-UP; 69Z1-UP)
3512 (S/N: 50Y1-UP; 66Z1-UP)
3516 (S/N: 29Z1-UP; 72Z1-UP)
Marine Auxiliary Engines:
3516 (S/N: 25Z1-UP)
Description of Change: New hydramechanical shutoff groups (HMSO) are used on these engines. The new hydramechanical shutoff groups have the following improvements:
A new gasket with adhesive backing is used in these groups. The new gasket will provide improved service life.
A new assembly procedure is used. The new procedure provides improved gasket retention. The new assembly procedure is listed later in this article.
A new plug with a smaller orifice is used in the pump cover. The smaller orifice reduces oil flow to the HMSO. This change helps prevent improper shutdowns. The new orifice plug also makes the HMSO more responsive to high water temperature events and low oil pressure events.
A new spring seat is used on the overspeed adjustment. The new seat has purge holes, in order to prevent buildup of oil pressure behind the seat. This change also makes the HMSO more responsive.Adaptable To: A cutaway view of the HMSO is shown in Illustration 1. The major components of the HMSO Groups are identified in Table 1.
Illustration 1 g00665618
Table 1
Identification of Components in the HMSO Groups    
Item     Description     New Part No.     Former Part No.    
1     Pump Cover     172-0263     5N-8484    
2     Gasket     172-0271     5N-8459    
3     Gerotor Pump     172-0265     5N-1925    
4     Seat     172-0264     3N-5748    
5     Control Housing Assembly     5N-6141     5N-6141    
6     Seal Plate     5N-8432     5N-8432    
7     Pipe Plug     172-0272     7N-4333    Illustration 2 shows the location of the new 172-0272 Pipe Plug.
Illustration 2 g00665775
(1) 172-0263 Pump Cover (7) 172-0272 Pipe Plug (X) View of Section B-BThe part numbers for the HMSO Groups are listed in Table 2. The new HMSO Groups are direct replacements for the former HMSO Groups. The former HMSO Groups are cancelled.Note: Because of limited usage, not all of the new HMSO Groups are available for parts service. The new HMSO Groups that are not serviced are called out in Table 2. To service these groups, order parts from the following Tables: Table 3, Table 4 and Table 5.Table 3 lists the components that are common to all of the HMSO Groups. Table 4 lists the springs that are required. The springs are specific to the governed speed of the engine. Table 5 lists the special fittings that are required for the HMSO Groups.
Table 2
Part Numbers for the Shutoff Control Groups (HMSO)    
Type of Protection     Engine Speed (rpm)     New HMSO Group Part No.     Former HMSO Group Part No.    
A (1)     1800     172-0255 (2)     5N-1960    
A     1500     172-0256     5N-5330    
A     1200     172-0257     5N-5329