D399, G399, D398, G398, D379, G379 ENGINES Caterpillar

A vibration damper counteracts torsional vibrations that occur within the operating speed range of the engine.

When an engine is running, the crankshaft twists back and forth about its axis due to the regular pattern of power impluses imposed along its length. This twisting of the crankshaft is called torsional vibration. A vibration damper installed on the end of the crankshaft opposite the flywheel helps to reduce torsional vibration and prevents it from building up to harmful proportions.

The damper is constructed of a solid cast iron weight (1) enclosed in a metal case (3). The small space (2) between the case and weight is filled with a viscous fluid that permits the iron weight to move in such a manner within the case as to damp the vibrations of the crankshaft.

TYPICAL VIBRATION DAMPER CROSS SECTION
1-Solid cast iron weight. 2-Space between case and weight. 3-Case.

If the case becomes dented, the viscous fluid may partially solidify or the case and iron weight may actually rub against each other. In either instance it will restrict the movement of the iron weight; and instead of damping crankshaft vibrations and reducing gear train noise, it may actually increase vibrations that could result in crankshaft failure. It will in most cases, cause excessive gear train noises "clatter" at varing points in the speed range.

Avoid welding, hammering or prying on the damper case. A damper that has the mounting holes worn oblong should be replaced.

The damper should be checked occasionally for dents or bulges in the damper case, and to see that mounting bolts are tight. A dented or bulged case requires that the damper be replaced. Damage can occur to the damper, the adapter, and to the crankshaft if the engine is operated with mounting bolts loose.

Install a new damper:

1 At major overhauls.

2 Any time a crankshaft failure (indicated as a tortional-type) has occurred.

3 Whenever a damper is found to be defective.

Damper Removal And Installation

1. Remove the fan group and radiator, if so equipped.

COVER REMOVAL (D399 Engine Illustrated)
1-Bolts. 2-Cover.

2. Install a 3/4" NC guide pin (5), 8 in. (203 mm) long for D398 Engines, 1" - 14 18 in. (457 mm) long for D399 Engines and two 1/2" - NC forcing screws (6) in the vibration damper (4).

3. Using the forcing screws (6), force the vibration damper (4) out on the guide pin (5) until a suitable hoist can be attached and the vibration damper removed. Approximate weight 125 lbs. (57 kg) for D398 Engines and 270 lbs. (122 kg) for D399 Engines.

NOTE: The damper is a single unit requiring no service. If it is damaged, it must be replaced.

PREPARING TO REMOVE THE VIBRATION DAMPER (D399 Engine Illustrated)
3-Bolts. 4-Vibration damper.

VIBRATION DAMPER REMOVAL (D399 Engine Illustrated)
4-Vibration damper. 5-Guide pin. 6-Forcing screws.

4. When installing the damper, apply 9S3265 Retaining Compound to bolt threads. On D399 Engine, tighten 1" bolts to torque of 560 - 720 lb. ft. (77,4 - 99,6 mkg). Tighten 3/8" bolts to torque of 27 - 37 lb. ft. (3,7 - 5,1 mkg). On D398 Engine, tighten adapter-to-crankshaft 7/8" bolts to torque of 345 - 405 lb. ft. (47,7 - 56,0 mkg) and damper-to-adapter 3/4" bolts to 210 - 250 lb. ft. (29 - 34,6 mkg).