2000/07/01 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

Illustration 2	g00665775
(1) 172-0263 Pump Cover (7) 172-0272 Pipe Plug (X) View of Section B-B

The 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.

Assembly Procedure

1. Clean the 5N-8432 Seal Plate (6) and the 172-0263 Pump Cover (1). All grease, oil, and other surface contaminants must be removed from the parts. Make sure that the parts are completely dry.

Note: Shake the 169-5464 Quick Cure Primer well before you apply the primer. Make sure that the temperature of the primer is above 0 °C (32 °F) before you apply the primer.

2. Apply 169-5464 Quick Cure Primer to the 5N-8432 Seal Plate and to the 172-0263 Pump Cover .

3. Allow one to two minutes for the primer to dry.

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Illustration 3	g00665657
This illustration shows the new 172-0271 Gasket (2). Apply a thin layer of 1U-8846 Sealant (Anaerobic) to area (A). The diameter of area (A) should be a minimum of 30 mm (1.18 inch).

4. Apply a thin layer of 1U-8846 Sealant (Anaerobic) to area (A) of the 172-0271 Gasket. Apply the sealant to both sides of the gasket. The sealant should be applied to an area of at least 30 mm (1.18 inch) in diameter.

5. Install the 172-0271 Gasket between the 172-0263 Pump Cover and the 5N-8432 Seal Plate. Complete the assembly process by fastening the 172-0265 Gerotor Pump (3) to the 5N-6141 Control Housing Assembly (5) .

6. Allow the assembled shutoff control group to cure for 24 hours before operating.