Torquing jam-nuts on rod-end bearings.

[johnp]

i know a lot of you just go for the "german torque" here (guten-tite), but i wanted to try to torque them. here's what i came up with.

i got a set of offset box-end wrenches (cheap, from harbor freight). i took the 9/16 and cut a gap in it so it would slide around the bearing, then i could put it down on the jam nut. but before i did, i drilled a hole in the handle, 5 inches from the center of the box. i also picked up a couple of fish scales from academy -- one is 0 to 20 pounds, the other 0-50 pounds. with the jam nut finger tight, i put the wrench on it, hooked the fish scale (spring balance) into the hole, and pulled until the balance read 35 pounds. i figure that's 175 inch-pounds. [i sure hope that's the correct torque for those buggers -- the thread is 3/8" diameter, and that's what the torque guide in chapter 5 says for 3/8 -- 160 to 190.] so, it might not be as accurate as a real torque wrench, but i figure it's alot closer than wingin' it.

the offset on the box-end was about an inch or so -- not enough to clear the rolled edge (i was doing elevators), but enough to clear the skin as it sticks out past the spar.

[drill_and_buck]

Anyone try torquing the jam-nuts with a crows foot and torque wrench?

I understand that there are some calculations you need to consider, but I haven't researched this yet.

-Mike
RV-8 Fuse
N468RV

[Thermos]

Mike,

That's how I tightened the jam nuts on my elevator and rudder. Worked fine, and the equation is pretty simple. Check out this website -

http://www.engineersedge.com/manufac...e_wrench_1.htm

for a good description of the process and a torque wrench extension calculator. Dan Checkoway also has a calculator on his website.

John,

Those jam nuts are AN316 shear nuts, and I think they have a lower torque spec than normal AN365 nuts. The Standard Aircraft Handbook has a table for both types, and if I recall correctly 3/8" AN316s only get torqued to 90-110 in-lbs...but check me on that - I don't have the book in front of me.

Hope this helps...

Dave

[johnp]

John,

Those jam nuts are AN316 shear nuts, and I think they have a lower torque spec than normal AN365 nuts. The Standard Aircraft Handbook has a table for both types, and if I recall correctly 3/8" AN316s only get torqued to 90-110 in-lbs...but check me on that - I don't have the book in front of me.

Hope this helps...

Dave

thanks, dave. i've got one of those books somewhere -- couldn't find it, so i went with the info i could find in chapter 5 of the van's manual. i'll do some more digging and find that book and check it out.

john