Prop Bolt Torquing

April 1987

Some builders seem to think that by "overtorquing" their prop bolts they can get around having to check the torque. This is not true. There is no way around the fact that you have to periodically check your prop bolts for correct torque. Overtorquing makes no sense and can crush the prop hub over a period of time until the bolts run out of thread and bottom out! Very dangerous since you are not now gripping the prop!

Your prop, once badly crushed, may not run true anymore, leading to vibration. Also, it is possible to ruin the threads in the drive lugs. The correct prop torque value for 3/8"-24 bolts is 200/250 inch/pounds (18/20 ft/lbs) for any 5 laminate wood prop, and 300 inch/pounds (25 ft/lbs) for the new multi-laminate wood props. For Defiants and those using the 7" diameter flange with 1/2-20 bolts, we have used 400/500 inch/pounds (33/42 ft/lbs) with no sign of crushing the new multi-laminate props.

Even so, you still have to periodically check your op bolts torque. This is true whether you fly a factory built Champ, Cub, or whatever. If it has a wood prop, it must be checked every 50 hours or so. If you move from a wet climate to a dry climate, check it more often.

Copyright 1999-2017 All Rights Reserved