Usage:
D379 Industrial, Marine And Generator Set Engines And G379 Natural Gas Engines
Correct installation of the crankshaft is very important. If the crankshaft assembly is installed backwards in the D379 and G379 Engines, the valve timing will not be correct. The valves can hit the pistons and the balancer gear position will not be correct. For installation purposes, the end of the crankshaft that must be installed toward the front of the engine has the letters "FRT" on the flange face. The end of the crankshaft that is to be installed toward the rear of the engine has a short line that is at least 6.4 mm (.25") long. This line is used for the alignment of the flywheel identification mark and the top dead center hole during assembly. The illustrations show the location of the marks on both ends of the crankshaft.
It is possible that some 3N2957 Crankshaft Assemblies have the "FRT" mark on the wrong end or the "FRT" mark was left off. To tell if the "FRT" mark is on the correct end of the crankshaft, or to identify the front if the mark was not put on the crankshaft, use the information that follows.
The information which follows permits the crankshaft to be checked for correct installation by removing only the flywheel on the rear of the engine and the vibration damper and adapter on the front of the engine. For a standard rotation engine, three teeth on the front crankshaft gear have punch marks. See Illustration 1. One tooth will have four to six punch marks along the top of the tooth. This tooth is used for alignment with the "C" mark on the 4L3407 Idler Gear which it runs against. This tooth is approximately 42° counterclockwise (as seen from the front) from the centerline of the number one journal. The centerline of the number one journal will be in alignment with the centerline of one of the threaded holes in the crankshaft flange. One tooth on the crankshaft gear will not be in alignment with the centerline of this hole.
Illustration 1. Location of identification is marked on front end of crankshaft.
To find the top center of the crankshaft number one journal when the crankshaft is installed in the engine, it will be necessary to use a dial indicator to find the top dead center position of the number one piston. This will put the top dead center position of the crankshaft 30 degrees counterclockwise from the vertical centerline as shown in Illustration 1 and 30 degrees clockwise as shown in Illustration 2.
Illustration 2. Location of identification marks on rear end of crankshaft.
The next two teeth counterclockwise (as seen from the front) have two punch marks along the length (top) of the teeth. These two teeth are used for alignment with the "R" mark on one tooth of the 4L3406 Idler Gear when the engine is changed to reverse rotation. There is only one marked tooth on the rear crankshaft gear. See Illustration 2. This tooth has four to six punch marks on the top. It has a location 30° counterclockwise (as seen from the rear) from the centerline of the last crankshaft journal. Since the teeth on the gear are 7.5° apart, one tooth will be in alignment with the center of a threaded hole in the crankshaft flange. The tooth with the four to six punch marks will be the fourth tooth.
This information permits a fast way to tell if the crankshaft is installed backwards, if the "FRT" mark was left off or put on the wrong end of the crankshaft. It does not tell if the teeth are marked correctly or in alignment when viewed with the damper or flywheel removed. It does permit a quick check to determine if the crankshaft is in backwards even if "FRT" isn't stamped on the crankshaft or is stamped on the wrong end. To check for correct tooth alignment of the gears, additional disassembly of the flywheel or front accessory housing is necessary.