HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Posted (7 years 11 months 2 weeks 2 days 19 hours ago) and read 1721 times:
On the Bolt-Nut Assy for the JT8Ds at the FCU Cross shaft to Start/Thrustr Cable attachment.The AMM states if a Locknut is used the Torque values of Bolt A is 50-70lb in[pound inch] & Bolt B is 100-140 lb in.
Whereas if a Castellated Nut is used the Torque Values reduce to 30-40 lb in & 60-85 lb in resp.
The question is Understandably that the Second method has a Split pin for added safety but why should the Torque values differ.
How is it determined that lower values will be needed for the Second method.
regds
MEL
NORTHSEATIGER From United Kingdom, joined Sep 2003, 432 posts, RR: 5 Reply 1, posted (7 years 11 months 2 weeks 2 days 19 hours ago) and read 1710 times:
I would think that the higher torque will be to "run down" the lock nut which I would imagine will be either eliptical or have a nylon coating, so the extra tq will deform the nut/cut the nylon and ensure the correct tq and locking where as with the split pin the tq is applied then the pin put through for safety.
Air2gxs From , joined Dec 1969, posts, RR: Reply 2, posted (7 years 11 months 2 weeks 2 days 11 hours ago) and read 1649 times:
Hawk,
Quite simply the cotter key takes the place of the torque. As you know, the property of elasticity is what allows fasteners such nuts, bolts, screws, etc. to hold, in conjunction with the locking system used, when torqued to the appropiate value. When using a cotter key we do not need to torque anymore than that required to bring the components together, unless the AMM calls for anything different.
In fact I know of one application where the torque is zero. On the CFM56 the VBV feedback cable is attached to the MEC with a bolt, nut washer and cotter key. There is a line item step to inspect that the nut/bolt assy is free to turn by hand.
Air2gxs From , joined Dec 1969, posts, RR: Reply 4, posted (7 years 11 months 2 weeks 11 hours ago) and read 1584 times:
In this particular application (VBV feedback), you want the fastest and most accurate response to the position of the VBV's, especially when moving into reverse. The zero torque allows an almost frictionless connection.
FredT From United Kingdom, joined Feb 2002, 2184 posts, RR: 26 Reply 5, posted (7 years 11 months 6 days 21 hours ago) and read 1530 times:
You have friction in the locking in the lock nut, which reduces the torque actually working to put traction on the bolt.
Compare it with wet and dry torque. If you use oil when tightening, you need less torque as less is being used to overcome friction. It is a common pitfall to put a bit of oil on when tightening a nut which is supposed to be tightened dry and has a torque specified accordingly. There you are left staring at your stripped (but well oiled) threads and wondering what just happened.
Cheers,
Fred
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