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Old 09-15-2009, 11:07 PM
smokenjoe50 smokenjoe50 is offline
Join Date: Jul 2008
Location: corona california
Posts: 74
Default Banjo bolt torque

When I torqued my fuel return line banjo bolt it snapped. I had to order a new one and that bolt cost 65 bucks
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Old 10-10-2011, 08:16 AM
Catbird Catbird is offline
Join Date: Oct 2009
Location: Birmingham, Alabama
Posts: 128

I'm buffaloed, stymied, confused, and concerned.

A few weeks ago when working through the fuel line clamp block assembly on Page 46-09, I removed the M8x1x17 Banjo Bolt and removed the orifice jet from the bolt per the instructions. Two pages later (Page 46-11), I torqued down the Banjo Bolt with the banjo fitting and two copper washers to 90 in-lb. No problem, except that I couldn't leave good enough alone. I wasn't quite satisfied with the position of the banjo fitting and the angle of the hoses, so removed the Banjo Bolt a second time. Upon retorquing to 90 in-lb, the bolt failed along the plane of the drilled holes in the shank. I assumed this was due to my fussing with it too much and ordered two (that's 2!) replacement Banjo Bolts at a total cost of $137!!!

When the replacement bolts arrived, I rechecked the setting on my torque wrench at 7.5 ft-lbs (90 in-lbs) and went to work. But before I got to 7.5 ft-lbs, the second Banjo Bolt failed in the same place, exactly like the first one. Upon close inspection, it's obvious that there is very little metal remaining in the shear plane where the holes are drilled. I grabbed the second replacement bolt (the third to be put in the hole) and switched to my in-lb torque wrench, which only goes up to 75 in-lb. I torqued this bolt smoothly to 75 in-lb, but could've sworn that it felt like the bolt was deforming (twisting) as I approached 75 on the dial. As much as I hate to admit it, I won't be satisfied until this third Banjo Bolt has been removed and replaced with a fourth one at an even lower torque.

Searching this forum, there has been very little discussion on the torque value for these Banjo Bolts. Has anyone else been having similar problems, or is it just me?
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Old 10-10-2011, 09:07 AM
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Lemmingman Lemmingman is offline
Join Date: Jun 2010
Location: McKinney, TX
Posts: 675

I know you've tried it on two separate wrenches, but have you considered the possibility your wrenches are out of calibration?
Gil Brice
McKinney, TX EAA-1246
RV7 - Working on fuse, fuel, brakes etc...
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Old 10-10-2011, 09:12 AM
Catbird Catbird is offline
Join Date: Oct 2009
Location: Birmingham, Alabama
Posts: 128

Yes, both wrenches have been calibrated. Has anyone else had this problem of breaking these drilled bolts?
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Old 10-10-2011, 12:40 PM
Mich48041 Mich48041 is offline
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,636

I read that first post (about the banjo bolt breaking) before I worked on mine. So I was very careful tightening the banjo bolt. Instead of using a torque wrench, I went by feel, basically turning until it felt tight, then turning another 10 degrees. There are lots of variables that affect bolt tension when using the torque method of tightening. Instead of torque, some engineers specify degrees of turning.
Here is a quote from:
Torque wrenches do not give a direct measurement of the clamping force in the screw, and indeed much of the force applied is lost just to overcoming friction.
More accurate methods for setting the clamping force rely on defining or measuring the screw extension; for instance, measurement of the angular rotation of the nut can serve as the basis for defining screw extension on thread pitch.
A quote from this website:
When you feel a bolt yield while being tightened, take it out and throw it away-don't even look at it
Since you have determined by experimenting that the banjo bolt fails when torqued to 90 inch-pounds, maybe the maximum torque should be 70 inch-pounds (based on the above references).
Joe Gores
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Old 10-10-2011, 01:08 PM
Catbird Catbird is offline
Join Date: Oct 2009
Location: Birmingham, Alabama
Posts: 128

Thanks, Joe, for the valuable info. The plans and instructions for the RV-12 are so complete and detailed that I sometimes forget to think, fixating instead on the torque values provided.

Considering the effects of a failure in flight of the Fuel Line Banjo Bolt (power failure due to loss of fuel pressure/flow to carbs and fire hazard due to gasoline leak on top of hot engine), I'll order two more Banjo Bolts and replace the third, which is suspect for failure. The fourth bolt will be torqued by feel instead of blithely reading the dial on the wrench.

California Power Sports is going to think I'm trying to corner the market on these banjo bolts.
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Old 10-10-2011, 01:56 PM
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DonFromTX DonFromTX is offline
Join Date: Oct 2010
Location: La Feria Texas
Posts: 3,746

I would still be concerned about just HOW close to breaking the bolt is when you have it tight. For my use, I would think of a better way to accomplish the mission.
The fuel pressure gauge I added to my Cummins Diesel had the same thing, I twisted the first one off before it even went to the spec. I drilled a hardened bolt myself, no problem now.
A&P, PP-SEL, Pathological Flier, EAA Technical Counselor
EAA Chapter 595 President,
Retired US Army Officer
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Old 10-10-2011, 02:28 PM
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GAHco GAHco is offline
Join Date: Dec 2006
Location: Paso Robles, CA
Posts: 1,177
Question Was it metric, or otherwise special?

Originally Posted by smokenjoe50 View Post
When I torqued my fuel return line banjo bolt it snapped. I had to order a new one and that bolt cost 65 bucks
My guess it was a Rotax special part. If it was AN banjo bolt I might have had what you needed?

Best wishes!
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