MS20074-05-06 torque question

[SomeGuyInCentralJersey]

Hello group, hoping experts can weigh in and clarify how to determine correct torque for alternator bracket to engine (RV14 390). These bolts are 5/16-18 course thread. AC 43.13 charts show specs for bolt and nut combo, but what about when the bolt goes into the engine?

 

[Pixair]

Engine Maintenance/Overhaul Manual has torques listed for all the fasteners on the engine. Google Service Table Limits Lycoming O390.

 

[Stevea]

It doesn't really matter that the bolt threads into the engine boss instead of into a nut. The bolted joint is still a 5/16-18 thread....so follow the toque spec for a 5/16-18 thread...,..80-90 inch pounds. AND, use p/n 10-1011 locking tab washer as shown in the drawing. These bolts get the "belt and suspenders" approach to thread locking, because the alternator is a relatively heavy mass, cantilever mounted off the engine as shown.

The required torque may (as suggested by Pixair) or may not be shown in the Maintenance manual. I don't remember if it is or not.......but if it is not listed specifically for that bolt, use the general table you listed above.

 

[Freemasm]

.......These bolts get the "belt and suspenders" approach to thread locking, because the alternator is a relatively heavy mass, cantilever mounted off the engine as shown....

Locking feature is required because they are installed in a blind hole.

Edit = Good question by the OP, BTW. Threading steel into a softer material could/should require some scrutiny.

 

[SomeGuyInCentralJersey]

90 inch pounds is no where near the 17 ft/lbs the lycoming documentation shows. Thanks Pixair.

 

[Stevea]

To quote Roseanne Roseannadanna, "Never mind."

 

[Tandem46]

- B&C manual states 110-150 in-lbs
- Superior manual list 200 in-lbs
- Lycoming manual (as already stated in post #5) lists 204 in-lbs