Broken bell crank attach bracket bolt

rickmellor · #1 07-24-2006, 02:17 AM

I feel like a total dork for this one. I was doing final assembly on the aileron bell crank in my 7A QB wing and I managed to twist the spar attach bolt off in the hole. It turns out that my fancy new inch pounds torque wrench doesn't work.

I had it set to 20 inch lbs and I snapped the bolt off without even thinking about it (blindly trusting the tool). Now I've gotta figure out how to recover without destroying the platenut. The leading edge skin is on so I can't reach it to replace it.

Do you guys have any tips for this? I've got a tap set on the way from Avery but I've never done this before and this is a bad place to be learning.

-Rick
RV7A QB (emp done, working on the wings)

rv8ch · #2 07-24-2006, 03:07 AM

I hope you get some better answers, but here's what I'd do. Drill a small hole in the center of the bolt, and get after it with an ez-out.

Avery sells them, and I'll bet you can get them at your local hardware store.

http://www.averytools.com/p-427-alde...w-remover.aspx

Dave Cole · #3 07-24-2006, 06:11 AM

If I understand you correctly, you were installing the aileron bellcrank bracket in the wing, and broke one of the attach bolts. If so, the broken bolt is threaded into a nut plate that is riveted to the tie-down bar, and the tie-down bar is bolted to the font side of the spar. With the fuel tank removed, you have easy access to the tie-down bar, so you can remove it and replace the nut palte.

rickmellor · #4 07-24-2006, 12:14 PM

Yes, this is exactly the problem. It doesn't look like the x-outs will work because the bolt head twisted off. However, I'm going to pick up a set of these and see if it'll work. They'll come in handy anyway, I'm sure.

I hadn't thought about getting at it with the tank off. I haven't done anything with the tank yet so it didn't even occur to me. Thanks for the suggestion, that'll work beautifully and I won't have to worry about the integrity of the fix.

-Rick
RV7A QB (emp done, working on the wings)

frankh · #5 07-24-2006, 12:27 PM

Do you think you must have put on the bolt?....To snap the bolt you must have put several times the torque required on the bolt...Or are these bolts weak?

Not critisising, just wondering how weak the bolts are??

Frank

rickmellor · #6 07-24-2006, 12:45 PM

It's an AN3 bolt so it's not too large. However, I'm a pretty strong guy and I have no sense for what 20 inch pounds feels like. After this my feeling is that it's not too much ... probably not much more than 'snug'.

I'm going to contact CDI and see if they can repair the wrench (or tell me how I'm using it incorrectly). The pic below is the wrench that I'm using. $149 from Avery.

Jekyll · #7 07-24-2006, 01:05 PM

Rick:

Are you new to using a click torque wrench? If not, disregard, if so, you may have just missed the indication. It can be very subtle depending on the wrench. Some give an audible click but most just give a small "yield" as you are pulling on the wrench. Make sure you use a VERY smooth and SLOW pull on all torque wrenches so that you can "feel" the subtle give.

Jekyll

rickmellor · #8 07-24-2006, 01:32 PM

Yes, this is my first attempt with one. I was expecting something like a ratchet effect once the set torque level had been exceeded ... kind of like the torque setting on my drill.

This model wrench is supposed to make a click sound when you reach the proper level ... I didn't hear one. After the nut broke I wanted to find out what was up so I put an extension in the vise, set the wrench down to the lowest level and tried to turn it. The thing would have broken before it clicked.

On a good note, I called Avery and they said to just return it for a full credit. They've never had one fail before, but maybe that's just my luck.

trib · #9 07-24-2006, 05:25 PM

That wrench looks awfully big, are you sure it wasn't 20 ft-lbs you were applying

. What is the torque range of the wrench? For reliable accuracy, the value should fall between 25% and 90% of the wrenches maximum value.

mlw450802 · #10 07-24-2006, 06:13 PM

Quote:

Originally Posted by rickmellor

Yes, this is my first attempt with one. I was expecting something like a ratchet effect once the set torque level had been exceeded ... kind of like the torque setting on my drill.

This model wrench is supposed to make a click sound when you reach the proper level ... I didn't hear one. After the nut broke I wanted to find out what was up so I put an extension in the vise, set the wrench down to the lowest level and tried to turn it. The thing would have broken before it clicked.

On a good note, I called Avery and they said to just return it for a full credit. They've never had one fail before, but maybe that's just my luck.

Rick,
If you've never used one of these wrenches before, the "click" at the lower torque settings can be barely audible and often is felt as much as heard.
The wrench does not have a clutch like your drill and if you continue to increase force after the torque setting is reached you can certainly break the fastener.
It might be best to set the wrench at a fairly high setting and try using it against a large fastener in your vise to get a feeling of the operation. The click will be more pronounced at the higher torques. Keep testing at progressively lower settings until you get used to what to expect when the setpoint is achieved.
Just remember, 20 in-lbs is only 2 lbs force on a 10 inch lever (2x 10).
That is not much.

-mike