Idler Stub Shaft Mounting Bolts; Idler Gear Sleeve Bearings Caterpillar

Reference: Service Magazine; June 14, 1993; Page 13; "Lock Removed From Front Timing Gear Group To Help Prevent Loss Of Tightening Torque".

Service Magazine; June 14, 1993; Page 14; "New Fuel Pump Drive Idler Gear Assembly And Shaft Used In Front Timing Gear Groups".

Problem:

There has been a recent increase in reports of front gear train failures. These failures have been the result of:

* Loosening of the bolts and nut mounting the fuel pump drive idler shaft to the front of the cylinder block.

* Idler gear sleeve bearing flaking.

This surge in failure reports may be related to the:

* Higher fuel pump injection pressures that are needed for the reduced emissions requirements of recent years.

* From the mixing of vintages of idler shafts and idler gear bearings.

Solution:

Engine Engineering is continuing to work on long term improvements to this problem, but for the short term, when the front housing has been removed for any reason, or after a gear train failure, take the following steps to minimize the possibility of the shaft mounting bolts/nut loosening or the idler bearing failures occurring:

1. Remove the two 0S-1618 Bolts (8) and 8N-4960 Plate (7) securing the fuel pump idler gear (6) to the idler shaft (3), and remove the idler gear assembly.

2. Remove the two 0S-1594 Bolts (2) and the one 5B-9079 (4) Nut that fasten the idler shaft (3) to the front of the cylinder block and remove idler shaft.

3. Inspect idler shaft mounting face and pilot for signs for wear. If the shaft does not have a "105-9772" part number stamped on the flange, or if the pilot diameter is worn below specification of 25.345 ± 0.013 mm (.9978 ± .0005 in), replace with a new 105-9772 Idler Shaft.

4. Inspect condition of pilot bore for the idler shaft in front of cylinder block. The pilot bore should be 25.311 ± 0.020 mm (.9965 ± .0008 in) in diameter and should not show signs of "wallowing out" of the bore.

5. Inspect the condition of 5S-8462 Stud in front of cylinder block. The stud must be tight, and the threads must not be unusually worn. Replace stud if necessary. Put a light coat of 9S-3263 Thread Lock on the stud threads prior to installation.

6. Reinstall 105-9772 Idler Shaft (3) in block. Be sure the idler shaft mounting flange is pressed flush against the front face of the cylinder block prior to installing the mounting hardware. You should note a tight fit when pressing the idler shaft pilot into the bore in the cylinder block. Use a soft-headed hammer or mallet to facilitate assembly.

7. Put a light coat of 9S-3263 Thread Lock on two new 0S-1594 Bolt (2) threads and to the stud threads. Use a new 5B-9079 Nut (4) on the stud. Tighten the two 0S-1594 Bolts and one 5B-9079 Nut to a torque of 50 ± 10 N·m (37 ± 7 lb ft).

8. Inspect fuel pump idler gear (6), fuel pump drive gear (1), and cam drive gear (5) for gear tooth wear or chipping. Replace if necessary.

9. Inspect idler gear bearing for chipping on the ends or deep scratches in the middle caused by sharp edges in the oil feed holes in the idler shaft. Either of these failure modes are possible with the former 8N-4959 Idler Shaft, even with the 2S-6692 Bearing. If the idler shaft must be replaced with a new 105-9772 Idler Shaft, press the old bearing out of the idler gear and replace with a new 2S-6692 Bearing. Do NOT use a 5S-7630 Bearing in an idler gear with the 105-9772 Idler Shaft.

10. Apply oil to the idler shaft. Install the idler gear (6) onto the idler shaft (3).

11. Inspect the 8N-4960 Plate (7). Replace the plate if there is any unusual wear. Make sure the markings on the plate are on the outside. Install the plate with two new 0S-1618 Bolts (8).

Front Timing Gear Group

COPYRIGHT 1997 CATERPILLAR ALL RIGHTS RESERVED