1977/06/08 Caterpillar

3408, 3412 Engines In All Applications

Description of Change: A number of improvements have been made to components of the fuel injection pump and governor on the above engines. Since most of these improvements are directly adaptable to earlier engines, this article gives a list of the changes so it can be used to check earlier pump and governor groups during reconditioning.

The changes have numbers to permit easy reference and identification with the illustrations.

1. Several changes to the governor oil pump increase the oil pressure at slow engine rpm. This improves governor action to prevent engine stall, especially when the rpm of a hot engine is rapidly lowered to low idle.

a. The thickness of the oil pump gears is increased from .250" (6.35 mm) to .375" (9.53 mm).

b. The outside diameter and number of teeth on the oil pump gears is changed, so the drive gear has 11 teeth and the idler gear has 9 teeth. Formerly, each gear had 10 teeth.

c. The drive gear now has a tighter press fit on the pinion so it will not work loose.

d. Because of the thicker gears, the oil pump cover is changed to use longer retainer bolts and the counterbore for the front bolt is not as deep.

2. An added O-ring seal is used on the outside diameter of the servo cylinder to prevent oil leakage between the cylinder and the governor plate assembly. Illustration 1.

Illustration 1. Changes 2, 5 and 6-governor.

3. The fuel ratio control is changed as follows (Illustration 3):

a. A bevel is added to the end of the control lever which makes contact with the fuel rack. This prevents possible contact between the lever and the fuel injection pump housing to make sure the lever operates freely.

b. The spring preload is decreased so it will give less resistance to the opposite force of the spring in the control linkage.

c. A.141" (3.57 mm) diameter hole added to the bottom of the bracket fits on a new slotted pin installed in the fuel pump housing. This prevents rotation of the bracket when the mounting bolt is tightened, and keeps the lever in correct alignment with the housing.

4. The fuel injection pump housing is changed to increase the thickness of the mounting boss and add a slotted pin for alignment of the fuel ratio control bracket. See Illustrations 4, and 5 or 6. The thicker mounting boss will prevent possible cracks in this area.

5. An increased spring preload is used in the linkage between the governor and fuel rack to give more positive operation, especially in conditions which cause a high resistance to movement. Illustration 1.

6. The governor control pin is now made of an alloy steel with higher strength to prevent possible cracks in the upper flange (.468"-11.80 mm diameter), and increased hardness for longer service life. Illustration 1.

Illustration 2. Changes 12 and 13-governor.

Illustration 3. Change 3-Fuel ratio control bracket assembly.

Illustration 4. Changes 4 and 8-Fuel injection pump housing.

Illustration 5. Changes 4 and 7-Fuel injection pump housing for 3408 Engines.

7. The surface area of the camshaft bearings is increased to extend bearing service life. Dimensions to install the new bearings are shown in Illustrations 5 and 6.

8. The bearings for the governor drive pinion are now longer to give more bearing surface, and the chamfer is removed from the outside diameter at one end. See Illustration 4. Removal of the chamfer improves the pump discharge pressure.

9. The governor shut-off lever has improved material specifications for more strength and better resistance to impact stresses. Illustration 7.

Illustration 6. Changes 4 and 7-Fuel injection pump housing for 3412 Engines.

Illustration 7. Changes 9 and 10-Governor control levers.

Illustration 8. Change 11-Shut-off solenoid.

10. Self-locking bolts are now used to hold all levers to the shut-off shaft. Illustration 7. Formerly, it was possible for vibration to loosen the bolts.

11. The electric shut-off solenoid now has a wider slot (notch) in the end of the shaft where it makes contact with the shut-off lever. See Illustration 8. This prevents side loads that can break the lever in some conditions.

12. A shorter right rear bolt is used to hold the governor cover to the governor housing. See Illustration 2. Formerly, it was possible for the bolt to make contact with the governor lever and limit the high idle.

13. Since the speed limiter has been removed (disconnected on earlier governors), the later governors are not machined for the speed limiter. Illustration 2.

14. On the "dashpot" 3% governor (generator set), the design is changed so the check valve assembly for the oil reservoir is now part of the cover assembly. With this design, the adapter plate between the governor housing and the cover assembly is not needed. Illustration 9.

Illustration 9. Change 14-Governor housing and cover.

15. A change to the fuel line fitting at the transfer pump outlet gives more clearance for a dial indicator. This permits the rack position to be checked during engine operation.

16. New fuel injection pump groups (basic) are used, including new plunger and barrel assemblies with a shorter plunger and stronger lifter assemblies. See the article "New Plunger and Barrel Assembly and Stronger Lifter Assemblies Used in Fuel Injection Pump Group" on Pages 3 and 4 of the December 8, 1976 Engine News.

17. A new seat for the governor spring is made in one piece to prevent loss of governor stability which can be caused by separation of the parts of the former seat. See the article "New Spring Seat Made in One Piece For Hydra-Mechanical Governors" on Page 4 of the September 13, 1976 Engine News.

Adaptable To: When the necessary parts are used together, the above changes are adaptable to all 3408 and 3412 Engines except as follows:

... Changes 1, 2, 5, 6 and 9 are not adaptable to engines equipped with Woodward governors.

... Changes 12 and 13 are not adaptable to engines equipped with either Woodward or "dashpot" 3% governors.

... Change 14 is adaptable only to engines equipped with "dashpot" 3% governors.

... Change 15 is adaptable only to 3408 Truck Engines.

INSTALLATION: For most of the changes, the new parts are direct replacements for the former parts and no special instructions are needed for installation. To install parts for changes 4, 7 and 8, use the information in the paragraphs that follow:

Change 4: To install an earlier 6N6964 Bracket Assembly for the fuel ratio control on a new fuel injection pump housing, it will be necessary to either remove the 8L6565 Slotted Pin from the housing or drill a.141" (3.57 mm) hole in the bracket. Special Instruction Form SMHS6996 gives complete information to make this change.

Change 7: The new camshaft bearings must be installed to the correct dimensions. See Illustration 5 or 6 for the engine model.

Change 8: Install the lower pinion bearing first, with the sharp edge that has no chamfer down. The top of the bearing must be below the oil hole, and the bottom of the bearing must not extend beyond the bore in the housing. Install the upper bearing with the sharp edge that has no chamfer up and flush (even) with the surface of the housing. Be sure the bearing is turned so the notch is in correct alignment as shown. See Illustration 4.