LINES GP-TURBOCHARGER OIL 4N3923 - Caterpillar

3412 Engines In All ApplicationsDescription 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