D343 REAR ENGINE FOR 666 AND 657 SCRAPERS Water Pump Drive Belt Caterpillar

Water Pump Drive Belt
1.1. Vibration Damper

The belt should be checked every 250 service hours for proper adjustment. If the belt is operated too loose it will slap against the pulleys causing unnecessary wear to the belt. If the belt is operated too tight, unnecessary stresses are placed upon the bearings and belts, which might shorten the life of both.

Adjusting Belt: To adjust the belt tension loosen the locknut (2). Turn the adjusting nut (1) until the belt can be pushed inward 1/2inch (1.27 cm.) as shown at (3) with a force of approximately 25 pounds exerted midway between the pulleys. Recheck the adjustment after tightening the locknut.

1-Adjusting nut. 2-Locknut. 3-Correct adjustment allows 1/2 inch (1.27 cm.) slack at this point.

Vibration Damper

The viscous type vibration damper, mounted on the fan drive pulley at the front of the crankshaft, reduces crankshaft vibration and gear train noise.

1-Solid cast iron weight. 2-Space between case and weight. 3-Case.


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.

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.

A viscous type damper that is operating correctly absorbs energy to damp out torsional vibrations and becomes much warmer than the surrounding engine parts. A damper that is not operating correctly will remain at approximately the same temperature as surrounding engine parts, which is probably 10° to 15° above ambient air temperature. Therefore, by feeling the damper after at least one hour of engine operation, a faulty damper may be detected.

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

Excessive heat can also damage a viscous damper. It is therefore necessary that adequate ventilation be provided around the damper to eliminate excessive heat. Complete enclosure of a viscous type damper should be avoided.

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

Whenever a damper is found to be defective it should be replaced.