Removing sheared bolts

Jeff R · #1 10-08-2007, 06:31 PM

Well, I got a brand new torque wrench so I could properly tighten all those bolts in my RV9. I first used it attaching the aileron bell crank mounting brackets to the wing spar. I looked up the suggested torque for an AN3 bolt and found 20 to 25 inch pounds (or at least that is what my brain thought it read). I set the wrench to 20 and thought as I was tightening the bolts that, "wow, that is a lot more force than I thought it would be". I tightened more than I was comfortable with and stopped before the wrench clicked.

Fast forward a week. I had to remove the bracket and I was surprised at how easily the bolts came out. I thougt "Didn't I really torque these in"? When I went to reinstall the bracket and bolts, I couldn't get the derned bolts to go in. I looked a bit closer and saw that all 4 bolts had sheared off inside the nut plate! Yikes! (I will avoid mentioning potential fates that could have befallen had I not discovered this.)

Did I use the right torque value or is my wrench terribly out of calibration (even though it is new and is supposedly in calibration)? And what is the best way to remove those bolts????

N941WR · #2 10-08-2007, 06:40 PM

Jeff,

Three things...

One, have you used a click type torque wrench before? The click on mine is very subtle and you can easily miss it.

Two, is your torque wrench for inch-pounds or foot-pounds?

Three, it is possible that your wrench is not calibrated correctly. You may have to return it.

kentb · #3 10-08-2007, 06:43 PM

Are you sure that your wrench is not calibrated in Foot Pounds instead of Inch Pounds?
When I torqued my AN3 bolts, it surprised me at how little effort it took. I don't remember the inch pounds, but the 20 sounds about right.

As for getting them out, you might hold out for a better answer, but I think that you will need to drill a hole through the bolt and then use an easy-out to remove the piece. Unless you can get to the other side. If that is possible I would try grabbing the part that sticks out with vice grips. Or what might work the best is to drill out the platenut and replace it.

Kent

szicree · #4 10-08-2007, 06:47 PM

The click gets stronger the higher the setting. At 20 inch-pounds it's almost nothing. With aircraft, if it feels like too much torque, it is. 20 inch-pounds is about what you get with a good twist on a screwdriver.

Captain Avgas · #5 10-08-2007, 07:11 PM

Quote:

Originally Posted by Jeff R

I looked a bit closer and saw that all 4 bolts had sheared off inside the nut plate!
And what is the best way to remove those bolts????

If you have snapped off the bolts in tension by over torquing then the nutplates will not be re-useable...there will certainly be damage to them as well. Nuts typically take three quarters of the load on just the first few threads.

If you have the fuel tank on the wing you'll have to take it off to get into the other side of the spar to remove and replace the nutplates. It's not a huge job.

Some people might recommend that you just attempt to remove the broken bolts and re-use the nutplate. Don't listen to them. Those are fasteners on a very critical component of the control system. If they fail in flight... you die.

Jeff R · #6 10-08-2007, 07:28 PM

The wrench is in inch pounds, but I guess I was thinking the wrench would give out when it reached the torque setting. I guess this type of wrench doesn't work this way. At least I didn't use it for other than those 4 bolts, as it sure seemed like I was applying a lot of force and I was going to test it out before using it again.

The fuel tank is off, so I can drill out the nut plates from the aft side of the spar and buck new rivets by reaching inside the leading edge?

And we weren't supposed to discuss what could happen with sheared bolts in the control system!

Thanks for all the replies.

terrykohler · #7 10-08-2007, 07:34 PM

Interesting that this thread pops up the same time as another thread on crummy, useless tools. If you really want an outstanding tool for aircraft, go to snapon.com and look up the QDRIVER4. This is an adjustable torque screwdriver that measures from 5 to 40 inch-pounds and can get into very tight spaces (empennage). Price is $177.00. Another great tool is their ratcheting stubby screwdriver. While not inexpensive, there are a number of good reasons why nearly every professional mechanic in America uses their stuff. If the prices scare you, keep shopping at Walmart and keep your expectations low.