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Aileron Bell-crank Binding

caapt

Well Known Member
Any one else have this problem? When I tork them down (85 inch/lbs) they bind up severely. The bellcrank is shorter than the brass bushing and even when they bind I can slide them up and down the bolt.
Any advice?
 
I had a similar problem with my RV-7 bellcranks. The inside bores were a bit rough at the welds, so I honed them out slightly with sandpaper taped to and wrapped around a dowel.

I also had a problem with a Dynon roll servo bracket that was misdrilled from the factory, causing the pivot bolt to bend slightly when torqued, and bind in the bellcrank. Dynon replaced the bracket at no charge, and the problem went away.

Hope this helps!
 
You don't need a new bellcrank. When they are welded the welds intrude into the tube the bushings fits into. Use the appropriate sized drill bit or reamer and clean out the welds inside the tube. This a very common issue.
 
mystery solved

Had my DAR take a look. The brass bushing (tube) is slightly bowed. Same problem with replacement tubes. By rotating the bushing in place we found a position that allowed free movement for that part of the arc that the bell crank needs to travel. Still binds up beyond that.
 
Had my DAR take a look. The brass bushing (tube) is slightly bowed. Same problem with replacement tubes. By rotating the bushing in place we found a position that allowed free movement for that part of the arc that the bell crank needs to travel. Still binds up beyond that.

Does this solve the problem? Is there any chance that it could become repositioned later and bind in flight?

Forgive me if I'm being an idiot, I'm trying to understand better for my own learning curve...
 
Any one else have this problem? When I tork them down (85 inch/lbs) they bind up severely. The bellcrank is shorter than the brass bushing and even when they bind I can slide them up and down the bolt.
Any advice?

If this is a brass bushing inside the weldment it is caused by the ends of the brass bushings not being square. When the bolt is tightened the brass bushing bows
 
Bellcranks

If this is a brass bushing inside the weldment it is caused by the ends of the brass bushings not being square. When the bolt is tightened the brass bushing bows

I had this problem but determined that it was a function of the steel brackets not being bent exactly 90 degrees. A good way to check this is to assemble the brackets, bushing and bellcrank on the bench and check for free bellcrank movement and parallel legs on the steel brackets. Mine were great on the bench but would drag when installed on the spar.
 
3rd set of bushings in the mail

Talked to vans. They are sending another set of bushings. We are at a loss. Bellcrank has been reamed. Brass bushing is longer than bell crank. All are binding.
 
I had a problem with mine binding once it rotated past a certain amount. Vans said to sand the interior but that didn't seem to help. I ordered a new one and a new bushing to see how those work. I was thinking that my bushings might not be square on the ends. I sanded them to final length on my HF 1" belt sander so they probably aren't perfectly square on the ends.

I may try to rig up some sort of fence thing to keep it square. I'm not sure if this has anything to do with my problem but hopefully with the options I now have with the new parts I can get it to work correctly.
 
Success!

Installed 3rd set of bushings. It was Easy! Minimal reaming for bolt insertion and installed. Worked first try! These bearings were straight
 
How I solved the problem

I had a problem with mine binding once it rotated past a certain amount. Vans said to sand the interior but that didn't seem to help. I ordered a new one and a new bushing to see how those work. I was thinking that my bushings might not be square on the ends. I sanded them to final length on my HF 1" belt sander so they probably aren't perfectly square on the ends.

I may try to rig up some sort of fence thing to keep it square. I'm not sure if this has anything to do with my problem but hopefully with the options I now have with the new parts I can get it to work correctly.

I had the same problems. Working on the parts myself helped a little, but did not completely solve the problem. The fact that the bushing fit well in some positions but not others told me something wasn't straight, but I didn't have the tools available to determine whether the bellcrank tube or the bushing was the main culprit. I took the parts to a local machinist to have them inspect the parts. The verdict was that both the bellcrank and the bushing were rough, and the bushing wasn't straight. He was able to smooth out the interior of the bellcrank tube, ream out the center of the bushing and polish the exterior enough to allow smooth operation without bringing it out of tolerance. The lesson here is that these are nice parts... but they aren't finished parts built to spec; they will require some fettling. He also recommended a superior lubricant for this application: Kluber Lubrication Isoflex Topas NB 52. It's waterproof and very clingy, yet lightweight with very little stiction, and it holds up better in use than most other greases would. There are other aerospace lubricants that may work as well... but he recommended the Kluber as being the best.
 
Another contributor to sticky bushings is over torquing the bolt, literally squeezing the bushing into the steel bellcrank tube. The OP was applying 85 in/lb to the bolt (mis-reading torque values in section 5.2), AN365- 1/4" nylocks should be torqued to 50 to 70 in/lb.
 
Another contributor to sticky bushings is over torquing the bolt, literally squeezing the bushing into the steel bellcrank tube. The OP was applying 85 in/lb to the bolt (mis-reading torque values in section 5.2), AN365- 1/4" nylocks should be torqued to 50 to 70 in/lb.

Thanks for supplying that torque spec; saved me some additional research. I bought some standard 1/4-28 and 10-32 nuts to use for bench testing the assembly. I discussed the cinch-binding with my machinist and he concurred with your assessment. Reaming the bushing will also alleviate that to some extent, but proper torque is the key.
 
Correction: I was TOLD Kluber was imported from Germany... but now that I'm looking at photos I took, I see "Made In USA" on all the various containers of it. So I guess it's made in the USA. That makes it seem more expensive... or maybe that's the reason why.
 
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