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-   -   rocker box bolt keeps snapping (http://xlforum.net/forums/showthread.php?t=1787009)

purpony 13th June 2014 13:29

rocker box bolt keeps snapping
 
I installed Buell XB rocker boxes on my Buell X1 a few years back and when i did the rear cylinder rear 1/4-20 grade 8 HD hex bolt snapped/sheered off on me. I have had my rockers off all winter and machined a drill guide and drilled this bolt out, and put a helicoil in the head. So i am installing the rocker boxes last night and torquing the bolts to spec and in the same location, the bolt snaps again!!! Im torquing them to what my service manual calls out - 10-14 ft/lbs. Pulled it all apart and lucky the way the bolt snapped I was able to just spin it out with pliers. Its a 1/4-20 grade 8 HD bolt and it snaps at 10 ft/lbs of tq, what gives?

cHarley04 13th June 2014 15:36

Just some thoughts/questions.
Are you sure the wrench is in calibration?
Torque wrenches are inherently not real accurate at the bottom or top of their range. For accuracy, you want to work in the middle of the wrenches range, not at either end.
For 10-12 ft/lbs, the better wrench choice might be something like a 20-250 IN/lbs wrench, torquing at 120-144 IN/lbs.
Are you using any extensions on the wrench and not recalculating for the extension factor?

Bob s hog 13th June 2014 16:00

better yet are you bottoming out the bolt g8 bolts are pretty taught . as stated above good tq wrench are a must.

aswracing 13th June 2014 16:04

ft-lb torque wrenches aren't real accurate that far down the scale.

I use an in-lbs torque wrench and torque to 150 and they don't break.

Wheelies 1st August 2014 14:15

The same happened to me on my front rocker box. I agree with the idea that torque wrenches suck at those low torque specs. My wrench clicked over fine on the rest of them but the very last one snapped off.

Folkie 1st August 2014 14:24

Torque wrenches are accurate at the top of the range, but not at the bottom.

rejeanprimeau 1st August 2014 14:41

I use a cheap beam type torque wrench ; never break bolt.

I love those clicker, I make money welding holes busted being over torque by clicker.

Keep clicking so we the machine shops and welders make money with your mistakes.

A 19.00$ sears beam type 3/8 is perfect for that job.


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