Earlier this week I adjusted the alternator belt tension, torqued the tension arm and pivot bolt, and safety wired them. The B&C installation instructions didn't have any info on the alternator belt tension, so Google to the rescue. Thanks to Mickey Coggins for putting the info where Google found it, and thanks to Vern Little for doing the original research and making the posting on the VAF WWW forum.

Vern Little's VAF WWW post:

Belt deflection is an unreliable method of tightening the belt.

Instead, use a torque wrench on the pulley belt 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!

ref Lycoming s. i. 1129A

Lycoming SI 1129A Accessory Drive Belt Tension

New 3/8 inch wide belt 11-13 ft/lbs 132-156 in/lbs. used 3/8 inch wide belt 7-9 ft/lbs 84-108 in/lbs

New 1/2 inch wide belt 13-15 ft/lbs 156-180 in/lbs. used 1/2 inch wide belt 9-11 ft/lbs 108-132in/lbs

Vern Little 9A