ENGINE CHANGES REVISED P/N'S (NEW OIL PUMP ASSEMBLY)

SUBJECT: W4 ENGINE CHANGES (NEW OIL PUMP ASSEMBLY)

VEHICLES AFFECTED: 1986-88 W4 FORWARD/TILTMASTER WITH 4B01-T ENGINE (VIN CODE H)

This bulletin has been revised to add revised part number for oil pump kit and oil pump kit installation instructions. This bulletin cancels and replaces Product Service Bulletin 88-6-508 dated November 7, 1988, all copies of which should be discarded.

Since the introduction of the 4BD1-T Engine in the W4 Truck, Isuzu has made continuous changes to this vehicle. Several of these product changes were effective with 1988 vehicles built after VIN number J7003969 (engine number 894348). Engine changes included revised:

1. Oil Pump - Trochoid (wheel) to gear type.

2. Oil Jet and Check Valve Assembly - Improved cooling of piston.

3. Piston - Revised internally.

Service Procedure:

Whenever a repair is performed which involves these components, it is recommended that the latest (Updated) parts be used for replacement.

Oil Pump Kit:

Upgrading from a trochoid (wheel) to gear type oil pump requires an oil pump kit, P/N 94055973. Included in the Oil Pump Kit is a set (four) of Oil Jets and Check Valves.

Note: Before installing the Oil Pump Assembly, apply a mixture of 20% MOS (Molybdenum Disulfide) and 80% engine oil to the Oil Pump Pinion Drive Gear.

The following procedure can be used to install the new style gear-type oil pump kit (P/N 94055973) in the above subject vehicles which were originally equipped with a trochoidal-type pump.

Service Procedure:

1. Drain engine oil.

2. Remove engine oil pan (Refer to 1988 W4 Service Manual, Page 6A6-42).

3. Remove two bolts (10) securing oil pump hole cover (9). Save bolts for later use, discard cover (Refer to Figure 1 when performing Steps 3 through 18).

4. Remove original oil pump drive pinion gear (7) from original oil pump shaft. Discard gear.

5. Remove four bolts (15) which secure the pump-to-block oil pipe (11). Discard bolts and pipe.

6. Remove two bolts (5) which secure original pump (4) to cylinder block. Discard bolts and pump.

7. Remove set screw (2) from cylinder block and discard.

8. Press out the original steel bushing (1) from the cylinder block's top side (drive the bushing upward). Discard bushing.

IMPORTANT: New partial engine assemblies are equipped with the new style bushing and, therefore, it is not necessary to remove when installing the new gear-type oil pump.

9. Install the new bushing (1) into the cylinder block with the two notches facing upward (as illustrated) until it bottoms.

NOTICE: To avoid damaging the bushing surfaces, use a brass drift punch (or equivalent soft faced tool) to drive in the new part.

10. Install the new set screw (2) into the cylinder block until flush with the outside of the block casting.

11. Slide new coupling (3) over splined end of new oil pump shaft.

12. Insert the new pump (4) (with coupling in place) into the cylinder block. Secure the pump to the block with two new bolts (5) (52 Nm, 38 ft/lbs.).

13. Slide new collar (6) over new pinion gear shaft (7). Coat the new pinion gear with moly grease (MoS2). Insert the pinion gear/collar (7) and (6) assembly into the cylinder block making sure that splined end of shaft properly engages with coupling, and that pinion gear is engaged with camshaft drive gear.

14. Insert new 0-ring (8) into new oil pump hole cover (9). Install cover (9) with original bolts (10) (26 Nm, 18 ft/lbs).

15. Remove any remaining pump-to-block oil pipe gasket material from block surfaces.

16. Install new pump-to-block oil pipe (11) with one gasket (12) at each end. Secure with four new retaining bolts (15) (26 Nm, 18 ft/lbs).

17. Remove four original check valves (14) and oil jets (13), and discard.

18. Install new oil jets (13) and check valves (14) (20 Nm, 15 ft/lbs).

19. Reinstall engine oil pan.

20. Fill engine with the proper oil.

Piston:

The new piston is interchangeable with the earlier piston. Whenever a piston/liner set is being replaced (before engine number 894348), it is recommended the new piston be installed in sets of four (4).

Oil Jet and Check Valve:

These assemblies are interchangeable with the earlier assemblies. Whenever upgrading, it is recommended that the Oil Jet and Check Valve Assemblies be replaced in sets of four (4).

Parts Information

Part Name Part Number ---------- ----------- Piston Grade (A) 94332538 Grade (C) 94332539

Liner Set Grade 1 94055975 Grade 2 94055976 Grade 3 94055977 Grade 4 94055978

* Oil Pump Kit 94055973 Oil Check Valve 94324049 Oil Jet Pipe 94319593

Partial Engine 94055974

Note: It is recommended when performing major engine repairs on vehicles built before VIN J7003969 (Engine No. 894348), the upgraded Piston/Liners and Oil Pump Kit be installed.

* Oil Pump Kit includes Oil check Valves and Oil Jet Pipes.

Parts are currently available from CANSPO.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.