Using Nylon Threads

by Gil Alexander

... here it is!! ... straight from the FAA mechanics bible .... AC43.13-1A "Acceptable Methods, Techniques and Practices - Aircraft Inspection, Repair and Alteration"
  1. Torque for clean, dry threads - no lubrication.
  2. You can use the manufacturer's recommendations (if you can find them!), measure the prevailing torque from the fibre locking ring, and add this torque to the recommended torque... OR ... you can use the figures from the table (quoted below) and just use them as a final torque.
  3. Apply a smooth, even pull, if any jerking motion occurs, back off and re-torque.
  4. Fibre lock nuts can be re-used any number of times, as long as the nut cannot be turned by finger pressure.
  5. Do not use fibre locking nuts on bolts with a drilled cotter pin holes in sizes less than 5/16. At 5/16 and above, make sure no burrs exist around the drilled hole.
  6. Self-locking nut/bolt combinations with NO cotter pin ARE OK for control systems as long as they clamp on an inner race of a bearing, and the bolt itself is not used as a pivot. This is the general RV control system arrangement, but there are exceptions.
SELECTED TORQUE VALUES from AC43.13-1A Chapter 5

AN bolt, AN365 nut (the usual RV combination)

#10 (AN3) 20-25 in.-lbs.
1/4 (AN4) 50-70 in.-lbs.

AN bolt, AN364 thin locknut
#10 (AN3) 12-15 in.-lbs.
1/4 (AN4) 30-40 in.-lbs.
If you use a high strength bolt (such as NAS1300 series) with AN365 locknut
#10 (AN3) 25-30 in.-lbs.
1/4 (AN4) 80-100 in.-lbs.
The all metal locknuts are usually rated the same as the AN365 fibre locknut.

OK .. for all of you who are not convinced by the FAA recommendations, Aircraft Spruce offers a "Belt and Braces" approach. They sell MS17825 self-locking castle nuts. This gives the best of both worlds, fibre locking AND a cotter pin, but at about a $1.00 each.

Get a copy of AC43.13, or borrow one from your friendly FAA Mechanic, it's well worth reading.

Gil Alexander RV6A #20701

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