Section 1.25
Compact Gear Train and Engine Timing

The compact gear train is completely enclosed between the gear case and gear case cover and is located at the front of the engine. The camshaft drive gear is part of the camshaft gear assembly and is located in the cover of the assembly. The gear train consists of a camshaft drive gear, camshaft idler gear, air compressor and power steering pump drive gear, bull gear, oil pump drive gear, crankshaft timing gear, water pump drive gear, accessory pulley drive gear, and adjustable idler gear. The gear train is lubricated by oil splash. The gear ratio of each gear in relationship to the crankshaft timing gear is shown directly below the gear title. See Figure "Compact Gear Train" .‪

Figure 1. Compact Gear Train

The crankshaft timing gear, pressed onto the front end of the crankshaft, directly drives the bull gear and oil pump drive gear, and indirectly (through the bull gear), drives the air compressor and power steering pump drive gear, accessory pulley drive gear and water pump drive gear.‪

The camshaft gear assembly must be in time with the crankshaft timing gear. Since there are three gears between them, timing marks have been stamped or etched on the face of the crankshaft timing gear and bull gear to facilitate correct gear train timing.‪

There are no timing marks on the drive gears for the air compressor and power steering pump, water pump, accessory drive pulley, adjustable idler gear or camshaft drive gear. Therefore it is not necessary to align these gears in any particular position during installation..‪

The lash between the various mating gears in the gear train should be 0.051 - 0.229 mm (0.002 - 0.009 in.) and should not exceed 0.305 mm (0.012 in.) backlash between worn gears.‪

Gear train noise is usually an indication of excessive gear lash, chipped, pitted or burred gear teeth or excessive bearing wear. Therefore, when noise develops in a gear train, the gear case cover should be removed and the gear train and its bearings inspected. A rattling noise usually indicates excessive gear lash whereas a whining noise indicates too little gear lash.‪

The correct relationship between the crankshaft and the camshaft must be maintained to properly control the opening and closing of the intake and exhaust valves, the operation of the fuel injectors and to help maintain engine balance.‪

An “out of time” engine may result in valve-to-piston dome contact, a no-start condition or loss of power.‪

Section 1.25.1
Repair or Replacement of Gear Train and Engine Timing

To determine if repair is possible or replacement is necessary, perform the following procedure. See Figures "Flowchart for Repair or  Replacement of Gear Train and Engine Timing – Part 1 of 3" , and .‪

Figure 2. Flowchart for Repair or  Replacement of Gear Train and Engine Timing – Part 1 of 3

Figure 3. Flowchart for Repair or Replacement of Gear Train and Engine Timing – Part 2 of 3

Figure 4. Flowchart for Repair or Replacement of Gear Train and Engine Timing – Part 3 of 3

Section 1.25.2
ENGINE TIMING

When an engine is out of time, the camshaft timing can be checked by following the camshaft timing check procedure. Refer to "1.28.6.1 Testing of Camshaft Timing for Diesel Engines" . If the engine is out of time, a visual inspection of the gear train is required. Refer to "1.11.2 Removal of Gear Case Cover" and perform all of the steps under "Removal of Gear Case Cover." ‪

Section 1.25.2.1
Check Engine Timing

Gear train noise is usually an indication of excessive gear lash, chipped, pitted or burred gear teeth, or excessive bearing wear. Therefore, when noise develops in a gear train, the gear case cover should be removed and the gear train and its bearings inspected. A rattling noise usually indicates excessive gear lash. A whining noise indicates too little gear lash.‪

1. Check engine timing as follows:
   1. Examine timing marks to ensure they are aligned. See Figure "Compact Gear Train and Engine Timing Marks" .
   

   1. Crankshaft Timing Gear‪	3. Bull Gear and Crankshaft Timing Gear Timing Marks‪
   2. Bull Gear‪

   Figure 5. Compact Gear Train and Engine Timing Marks

   2. It may be necessary to remove the gears to align the timing marks of the bull gear and crankshaft timing gear. See Figure "Compact Gear Train and Engine Timing Marks" .
   3. If any gears are removed or installed, or if lash between any two gears is out of specification, check the lash between the mating gears.
2. Check the crankshaft timing gear-to-oil pump idler gear lash measurement as follows:
   1. Fasten a dial indicator and magnetic base to the cylinder block so that the stem of the dial indicator rests on a tooth of the oil pump drive gear. See Figure "Crankshaft Timing Gear-to-Oil Pump Idler Gear Lash Measurement" .
   

   Figure 6. Crankshaft Timing Gear-to-Oil Pump Idler Gear Lash Measurement

   2. Hold the crankshaft timing gear stationary, and rotate the oil pump drive gear in one direction, as far as it will go, without moving the crankshaft timing gear.
   3. Zero the dial indicator.
   4. Move the oil pump drive gear in the opposite direction, as far as it will go, without moving the crankshaft timing gear.
   5. Read and record the total gear lash.

   Note: The gear lash must be checked in four positions 90 degrees apart.

   Note: The lash between the crankshaft timing gear and oil pump drive gear must be measured with the engine assembled and positioned to run. See Figure "Crankshaft Timing Gear-to-Oil Pump Idler Gear Lash Measurement" .

   Proper lash between the crankshaft timing gear and oil pump drive gear is 0.051-0.229 mm (0.002 -0.009 in.). ‪

   The gear lash between the crankshaft timing gear and the oil pump drive gear can be adjusted utilizing shims inserted between the oil pump body and the cylinder block. See Figure "Lubricating Oil Pump Shim Installation" .‪

   

   Figure 7. Lubricating Oil Pump Shim Installation

   6. Remove or install shims as necessary to obtain the proper gear lash clearance.

   Note: When adjusting for gear tooth lash by installing or removing shims, the same number of shims must be changed under each foot so that the pump will always be level on the engine block. The insertion or removal of one 0.127 mm (0.005 in.) shim will change the gear tooth lash by approximately 0.102 mm (0.004 in.).

   Note: If it is necessary to remove the oil pump, refer to "3.2.2 Removal of Oil Pump" .

   7. If the use of shims cannot bring gear lash within acceptable limits, the gear or gears for that gear set must be replaced.
3. Check the crankshaft timing gear-to-bull gear lash measurement as follows:
   1. Install a dial indicator and magnetic base. See Figure "Crankshaft Timing Gear-To-Bull Gear Lash Measurement" .
   

   1. Bull Gear‪	3. Crankshaft Gear‪
   2. Dial Indicator‪

   Figure 8. Crankshaft Timing Gear-To-Bull Gear Lash Measurement

   2. Adjust the stem of the dial indicator to rest on the center of a tooth on the bull gear.
   3. Preload the bull gear.
   4. Zero the dial indicator pointer.
   5. Hold the crankshaft timing gear stationary with one hand. Rotate the bull gear and check the total gear lash in four positions of crank gear, approximately 90 degrees apart.
   6. Although gear lash for the remaining gear sets is not adjustable, the lash must still be measured. Lash specifications is 0.051-0.229 mm (0.002-0.009 in.) for new parts and a maximum of 0.305 mm (0.012 in.) for used parts.
   7. If lash measurement is exceeded, replace gear with a new part.
4. The procedure for measuring the lash between the bull gear, air compressor and power steering pump drive gear is similar to the steps just mentioned. Refer to step 3 and perform step 3a , as the first step and refer to step 3g , as the final step.

   Gear case cover must be installed to continue on checking the engine timing. Refer to "1.10.3 Installation of Gear Case Cover" and perform all of the steps under gear case cover installation. ‪

   Note: Due to the possibility of damaging the crankshaft front oil seal, whenever the gear case cover is removed, the front crankshaft oil seal must be replaced. Replace the crankshaft front oil seal after the gear case cover is installed. Refer to "1.8.5 Installation of Front and Rear Crankshaft Oil Seal and Wear Sleeve" .

5. The procedure for measuring the lash between the accessory drive gear and air compressor pump drive gear (on vehicle without power steering) is similar to the steps just mentioned. Refer to step 3 and perform step 3a , as the first step and refer to step 3g , as the final step.

   Note: Lash can be measured with the gear case cover installed. Access covers are provided for checking the lash between these gears and the bull gear.

6. The procedure for measuring the lash for the adjustable idler gear is similar to the steps just mentioned. Refer to step 3 and perform step 3a , as the first step and refer to step 3g , as the final step.

   Note: These gears are measured with the gear case cover installed.

7. The procedure for measuring the lash between the bull gear and the water pump drive gear is similar to the steps just mentioned. Refer to step 3 and perform step 3a , as the first step and refer to step 3g , as the final step.

   Note: These gears can be measured with the pump installed.

8. Check the bull gear-to-accessory drive gear lash measurement as follows:
   1. Install the gear lash tool (J–38662) and mount a magnetic dial indicator base and dial indicator to the gear case cover. See Figure "Accessory Drive Gear-to-Bull Gear Lash Measurement" .
   

   Figure 9. Accessory Drive Gear-to-Bull Gear Lash Measurement

   2. Position the dial indicator to read between the scribed lines on the tool. See Figure "Accessory Drive Gear-to-Bull Gear Lash Measurement" .
   3. Rotate the accessory drive pulley, read and record the total gear lash.
   4. Gear lash measurements are 0.051-0.229 mm (0.002 -0.009 in.) for new parts, and 0.305 mm (0.012 in.) for used parts.
   5. If proper lash measurement cannot be obtained, replace gear with a new part.
   6. Remove the dial indicator and gear lash tool.
9. Check the bull gear-to-water pump drive gear lash measurement with water pump gear lash tool (J–38977–A) as follows:
   1. Remove the pipe plug in the gear case cover.
   2. Install the water pump gear lash tool (J–38977–A) through the hole in the gear case and thread it into the special water pump drive gear retaining bolt. See Figure "Water Pump Gear Lash Tool Method" .
   

   Figure 10. Water Pump Gear Lash Tool Method

   3. The arm of this tool has an inscribed line. Measuring with a dial indicator at this line of the tool, the gear lash measurement will be an exact 1:1 reading. Gear lash specifications are 0.051-0.229 mm (0.002 -0.009 in.).
   4. If proper lash cannot be obtained, replace the gear with a new part.
   5. Remove the dial indicator and the gear lash tool.
   6. Install the pipe plug in the gear case cover. Torque to 24-31 N·m (18-23 lb·ft).
10. Check the bull gear-to-air compressor drive gear lash measurement as follows:
    1. Mount a magnetic dial indicator base and dial indicator to the gear case cover so that the stem of the dial indicator may be positioned on a tooth of the air compressor drive gear.
    2. Preload the drive gear in one direction.
    3. Zero the dial indicator.
    4. Rotate the air compressor drive gear, read and record the total gear lash. Gear lash measurements are 0.051-0.229 mm (0.002 -0.009 in.) for new parts, with a maximum of 0.305 mm (0.012 in.) for used gears.
    5. If proper lash cannot be obtained, replace the gear with a new part.
    6. Remove the dial indicator and magnetic base.
    7. Install the power steering drive coupling to the air compressor drive gear (if equipped with power steering) and insert a new O-ring on the power steering pump (if so equipped).
    8. Install the power steering pump to the gear case cover, meshing the drive coupling properly.
    9. Install and torque the power steering pump mounting bolts to 30-38 N·m (22-28 lb·ft). Tighten the five bolts alternately and evenly, in a star-shaped pattern, to progressively draw the power steering pump into the gear case cover.

    Note: Do not force the bolts. If resistance is encountered, remove the power steering pump and re-engage the drive hub with the coupling.

    10. If the engine is not equipped with power steering, install the air compressor drive gear access cover using a new gasket.
    11. Install and torque the retaining bolts to 30-38 N·m (22-28 lb·ft), using a star-shaped pattern.

Section 1.25.2.2
Engine Timing for the Compact Gear Train Assembly

The procedures for measuring and adjusting the gear lash for the compact gear train are as follows:‪

1. If the camshaft gear assembly has been removed, refer to "1.26.5 Installation of Camshaft Bearings and Camshaft Gear Assembly" for installation instructions.
2. With the camshaft gear assembly installed, remove idler gear centering tool ( J–46306–A ) see Figure "Idler Gear Centering Tool (J–46306–A)" and camshaft gear alignment tool ( J–45946 ). See Figure "Camshaft Gear Alignment Tool (J–45946)" .
   

   Figure 11. Idler Gear Centering Tool (J–46306–A)

   

   Figure 12. Camshaft Gear Alignment Tool (J–45946)

3. Remove two plugs located on gear case cover. See Figure "Idler Gear and Bull Gear Access Holes" .
   

   1. Plug‪	3. Bull Gear Access Location‪
   2. Idler Gear Access Location‪

   Figure 13. Idler Gear and Bull Gear Access Holes

   Note: Gear lash measuring tool (J–46303) is magnetized.

4. Install the gear lash measuring tool (J–46303) onto the center of the camshaft drive gear at the three o'clock position. See Figure "Compact Gear Train Gear Lash Measurement" .
5. Attach the magnetic base on dial indicator to the camshaft gear cover. Adjust the stem of the dial indicator to rest on the flat of measuring tool ( J–46303) at the scribe line on the bar at a 90° angle. Zero the dial indicator. See Figure "Compact Gear Train Gear Lash Measurement" .
   

   1. Adjustable Idler Gear Retaining Nut‪	3. Dial Indicator‪
   2. Magnetic Base‪

   Figure 14. Compact Gear Train Gear Lash Measurement

6. If the adjustable idler gear has been removed, torque the three nuts that retain the adjustable idler gear hub to the gear case to 57-67 N·m (42-49 lb·ft) to seat the assembly before proceeding.
7. Loosen the three nuts that retain the adjustable idler gear hub to the gear case until they are hand tight.
8. Insert the dowel portion of the gear lash adjusting tool (J–35596–A) through the hole in the adjustable idler gear retaining plate and into the adjustable idler gear hub, using the bottom two adjustable idler gear cover bolt holes. See Figure "Compact Gear Train Gear Lash Measurement" .

   Note: Ensure screwdriver is inserted between camshaft and idler gear teeth and not on the perimeter of the gear, incorrect insertion of the screwdriver will result in incorrect lash measurement readings.

   Note: Do not apply side load with the screwdriver; prying the gears will result in incorrect lash measurement readings.

9. Insert a screwdriver through the idler gear access hole provided in the gear case cover. Engage the screwdriver between two of the idler gear teeth and apply pressure on the screwdriver to secure the gear. This will prevent the gear from moving. See Figure "Compact Gear Train Lash Adjustment" .
   

   Figure 15. Compact Gear Train Lash Adjustment

10. Zero the dial indicator.
11. Using a rag to protect against the sharp edges of the camshaft, rotate the camshaft by hand and observe the dial indicator pointer.

    Note: Turn the adjuster on tool J–35596–A clockwise to decrease gear lash and counterclockwise to increase gear lash.

12. Secure the adjustable idler gear with a screwdriver; refer to step 9 .
13. Turn the adjusting screw of the gear lash adjusting tool (J–35596–A), approximately 1-1/2 turns. Gear lash should be 0.051-0.229 mm (0.002-0.009 in.). Repeat steps 11 and until proper lash is obtained.

    Note: If there is zero lash between the two gears, the dial indicator pointer will not move from zero.

    Note: Torque idler gear nuts first to prevent any gear movement which would change gear lash settings.

14. When the proper readings of 0.051-0.229 mm (0.002-0.009 in.) are obtained at all four positions, secure the idler gear and torque the three adjustable idler gear nuts to 103-113 N·m (76-83 lb·ft.).
15. Check the gear lash with the measuring tool (J–46303) at 3, 6, 9, and 12 o'clock positions.
16. Remove the gear lash adjusting tool (J–35596–A), measuring tool (J–46303) and the dial indicator.
17. If proper lash measurement cannot be obtained, replace gear(s) with new part(s).
18. Before installing the rocker arm shaft assemblies, check the torque on the end studs to ensure they were not loosened at the time of removal. The torque specification is 101-116 N·m (75 -86 lb·ft).
19. Install the rocker arm shaft assemblies to the cylinder head. Refer to "1.3.3 Installation of Rocker Arm Shaft Assembly" .
20. Adjust the intake and exhaust valve clearances, and fuel injector heights. Refer to "13.2 Valve Lash, Injector Height (Timing) and Jake Brake® Lash Adjustments" .
21. Install the valve rocker cover. Refer to "1.6.8 Installation of One-Piece Rocker Cover" for a one-piece valve rocker cover and refer to "1.6.9 Installation of Two-Piece and Three-Piece Rocker Covers" for two-piece and three-piece rocker covers.
22. Install the camshaft drive gear access cover. Torque the five bolts to 30-38 N·m (22-28 lb·ft) and install the two plugs into the gear case cover and torque the plugs to 38-42 N·m (28-31 lb·ft).

Section 1.25.3
Installation of Removed Compact Gear Train Components

After all of the gear lash measurements have been taken, assemble the engine components as follows:‪

1. Install the air conditioner compressor and brackets (if so equipped). Install the air conditioner drive belt.
2. Install the alternator and brackets. Refer to "9.2.3 Installation of Alternator" .
3. Install the alternator drive belts. Refer to "14.6.9 Drive Belts" .
4. Install the fan and fan hub assembly. Refer to "4.6.6 Installation of the Engine Cooling Fan" .
5. Adjust the alternator, fan and air conditioner compressor drive belts to specifications. Refer to "14.6.9 Drive Belts" . Torque the accessory mounting bolts to specifications.
6. Install any other equipment such as hoses, brackets, lines or electrical looms that were removed to gain access to the engine gear case cover.
7. Install the engine oil pan. Refer to "3.11.4 Installation of Oil Pan" .
8. Fill the engine crankcase. Refer to "14.6.1 Lubricating Oil" .
9. Refer to "12.7 Engine Run-in Instructions" for verification of proper gear train and engine timing.