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TENSION CHECKING & ADJUSTING

Fig. 1: A gauge is recommended, but you can check belt tension with thumb pressure

Fig. 2: Various belt tension adjustments on the diesel engine

Fig. 3: Alternator belt tension adjustment

Fig. 4: Rotary engine belt tensioning points

Fig. 5: Some belts have adjuster pulleys that allow you to tighten and loosen tension simply by turning a screw . . .

Fig. 6: . . . while others require you to pry on them to tighten tension and push on them to loosen

Fan Belt
  1. Apply thumb pressure (about 22 lbs.) to the fan belt midway between the pulleys and check the deflection. It should be approximately 3⁄8 in. for new belts and 1⁄2 in. for used belts.
  2. To adjust the tension, loosen the alternator mounting bolt and adjusting bolt.
  3. Move the alternator in the direction necessary to loosen or tighten the tension.
  4. Tighten the mounting and adjusting bolts and recheck the tension.
Thermactor Air Pump Belt
  1. Check the air pump drive belt tension by applying thumb pressure at a point midway between the air pump pulley and the crankshaft pulley. The deflection should be 1⁄2 – 5⁄8 in.
  2. If the tension is not correct, loosen the mounting and adjusting bolts slightly.
  3. Pry the air pump outward (or inward) until the proper deflection is obtained.
  4. Tighten the adjusting and lower bolts to 22 ft. lbs.

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