Alternator Belt Tension

18 Apr 2006 Alternator Belt Tension

From Vern Little on the Van’s Air Force website:

Belt deflection is an unreliable method of tightening the belt.

Instead, use a torque wrench on the pulley nut and adjust the tension so that you get about 12 ft-lbs before the belt slips.

A loose belt can lead to under-voltage or over-voltage from the alternator. Overvoltage is caused by the regulator trying to force more output from the alternator while the belt is slipping. When the belt grabs, it puts a surge of voltage on the bus.

Please don’t ask me how I found out!

Lycoming SI 1129A Accessory Drive Belt Tension

New 3/8″ 11-13 ft/lbs 132-156 in/lbs
Used 3/8″ 7-9 ft/lbs 84-108 in/lbs

New 1/2″ 13-15 ft/lbs 156-180 in/lbs
Used 1/2″ 9-11 ft/lbs 108-132in/lbs

Vern Little 9A