HT4100 ENGINE ACCESSORY DRIVE BELT TENSIONING

Jack screw adjusters are used for tensioning drive belts on most HT4100 engine accessories. Using an improper jack screw adjustment procedure may result in an overtensioned drive belt causing an increased load on both the engine crankshaft and the specific accessory bearing. An overtensioned belt may be diagnosed as an engine or accessory noise and/or vibration.

Overtensioning may occur if the accessory component pivot and adjustment slot bolts are excessively loose allowing the accessory to rotate towards the front of the engine as the jack screw adjustment is made. Consequently, when the bolts are tightened, the accessory is forced back to its normal position resulting in an overtensioned belt.

To avoid accessory drive belt overtensioning, use the following jack screw adjustment procedure:

1. Loosen pivot and adjuster slot bolts only enough to allow accessory movement. Do not loosen excessively. (Also loosen rear support when adjusting A/C compressor drive belt.)

Install belt tension gage, J-23600, midway between pulleys on belt being adjusted.

3. Turn jack screw adjuster until specified belt tension is indicated on gage (refer to Figure 1).

4. Remove belt tension gage.

5. Tighten adjuster slot bolt first and pivot bolt second to specified torque (also tighten rear support when adjusting A/C compressor drive belt).

6. Reinstall belt tension gage to check that belt tension did not increase due to tightening of bolts.

7. If belt tension is incorrect, repeat procedure.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.