PROPELLER TORQUE- a basic primer
The torque specifications for propellers are generally a propeller manufacturer specification. Torque varies for Wooden or Metal propellers, and based upon bolt size and bearing area on the hub.
For wood propellers, Sensenich has a very good tech article on proper installation "torque". Their position is that it's more about wood crush and height of the hub, than torque. See table 1.
A base line torque for Wood props (direct mounted) is:
3/8 in bolt 200+/- 25 in-lbs
7/16 in. bolt 250 +/- in- lbs
½ in. bolt 300 +/- in-lbs
Torque for mounting in a propeller hub is:
3/8 in bolt 23-25 ft-lb, 280-300 in-lbs
7/16 in. bolt 40-45 ft-lb, 480-540 in- lbs
½ in. bolt 60-65 ft-lb, 720-780 in-lbs
Sources are Sensenich Wood Propellers; Installation, Operation, and Maintenance, Integral Flange Crankshafts
The Continental Engine overhaul manual calls for 200-220 Inch/Pounds, or 16.7 to 18.3
FT.Lbs, OR 23 to 25,3 meters/Kg
For Sensenich Metal Propellers:
3/8 inch bolts use 23 to 25 lb-ft (280 to 300 lb-in) (31.6 to 33.9 newton-meters)
7/16 inch bolts use 40 to 45 lb-ft (480 to 540 lb-in) (54.2 to 61.0 newton-meters)
½ inch bolts use 60 to 65 lb-ft (720 to 780 lb-in) (81.3 to 88.1 newton-meters)
For metal props, McCauley also has an excellent service bulletin (SB 227B) on mounting bolt torque values.
The torque value for fixed pitch metal McCauley propellers is based on the propeller mounting bolt size.
For a 3/8" prop bolt, the torque is 25-30 pound-feet or 300-360 pound-inches.
Continental Engine Tapershaft Propeller Hub Torque
Torque for the taper shaft propeller adapter is located in the A-65, 85, and O-200 manual. Section 6-4 Propeller Installation.
The torque is 200 to 225 FOOT-Pounds for the center retaining nut with the (4) holes in it.
IE using a 3 foot bar, Pull approximately 70# for full tightness of the Hub on to the tapered crankshaft.
These hubs should be inspected at each removal for cracks in the hub at the keyway and between the lightening holes. These cracks propagate quickly and can result in catastrophic failure. The hub cracks can be induced by over torquing the hub to the crankshaft.
Copyright © 2004, Douglas Combs
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