How can I get out my flap stop bolts? They appear to be both rusted and painted in place. I tried to loosen one, but the nut part seems to be turning in its hole in the bracket.
Search strings: flap bumper bolts, flap adjustment bolts, flap up-stop bolts
Technical Editor:
Virtually every plane I see has badly rusted stop bolts in the outboard flap stop bracket. In many cases they have the incorrect bolt installed, leading to the head of the bolt chewing up the stop bracket. Sometimes a standard AN3 bolt has been installed, with insufficient threads for proper adjustment.
These bolts should be proper Cad-plated, MilSpec adjustment bolts. They have very high strength, have threads for most of their length, and have the proper crowned (slightly domed) heads, with recessed head stamps. These can be very hard to find in the needed dash 3 size. You should also use a new AN316-3L (thin) Cad-plated check nut with each bolt.
The best time to replace these is when the flaps are being readjusted anyway (though they can be changed any time). You’ll need to apply Corrosion X and let it soak for a week, if the old bolts are rusty.
The bolts are mounted in a Riv-Nut. Those things are a royal pain if they start spinning on you. To remove each bolt, first break loose the check nut. Then snug it back down, and back out the bolt while using the check nut to hold the head of the RivNut clamped against the bracket face. If it isn’t hard to back out the bolt, you don’t have the check nut clamped down tightly enough. Once you have successfully removed the old bolt, you must do two more things to ‘save’ the old Riv-Nut. Gently clean out the Riv-Nut threads with a 10-32 hand tap. Then try to ‘re-set’ the Riv-Nut.
If you do not have a setting tool, you can get by with re-setting it using the new bumper bolt and check nut. Install the bolt with the nut on the shank, and a flat washer under the nut. Make sure that the bolt threads go completely through the Riv-Nut. Then snug down the check nut pretty tightly, clamping the washer against the Riv-‘Nut. Loosen the nut, take the bolt out to remove the washer, and reinstall the bolt and nut assembly. Make sure that the bolt will move in the Riv-Nut with no more than a slight drag. If necessary, clean out the Riv-Nut threads again.
Once the flaps have been properly adjusted in the up position, the flap drive rod secures the inboard end. The outboard stop bolt should be adjusted so that it keeps the flap from ‘chattering’, but not so tightly that it warps the outboard end of the flap aft.
I like to set the flap adjustment all the way up, nested into the wing, with the FAA-approved Teflon chafe tape (from Spruce) applied to prevent wear from the wing skin. Do a BAC search on ‘flap adjustment’ for more information.