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  #1  
Old 07-24-2016, 03:03 PM
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spaceflightmeow spaceflightmeow is offline
 
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Default Torqueing AN818 nuts for vent and fuel lines?

I'm working on installing the vent tube in the RV-7 fuel tank but I'm puzzled on how to torque the AN818 nut.

The tank vent tube is 1/4" 3003 AL and takes a AN818-4D nut. AC43.13 says to torque the nut to 40-65 in-lbs. I have a 1/4" drive torque wrench (20-150 in-lbs). I need a 9/16" crowfoot in a 1/4" drive, which I cannot find. It seems most crowfoot wrenches are 3/8" drive, but virtually all 3/8" drive torque wrenches can barely get down 65 in-lbs (5.4 ft-lbs).

Also I've seen people tighten the nut so many flats. How many turns is needed for a AN818-4D nut on a 3003 tube?
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  #2  
Old 07-24-2016, 03:17 PM
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Default 3/8 - 1/4 adapter

Why can't you use a 3/8 to 1/4 adapter for the crowsfoot? Extensions do not change the torque. Just turn the crowsfoot 90? to the Tq wrench.
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Old 07-24-2016, 06:48 PM
deek deek is offline
 
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I'd just "tighten" it... but if you wish to torque it simply use your 9/16" open/box combo wrench and measure the distance from the nut CL to the center of the box. Do the math and hang the requisite weight from the box end.

For example, if your combo wrench had a 12" arm you'd hang a 4# weight from the box end and Bob's your Uncle.
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Old 07-24-2016, 07:47 PM
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I got a 3/8 to 1/4 adapter and a 3/8 crows foot set, installed the crowfoot at 90 deg to the torque wrench and torqued a couple of test fittings to 65 in-lbs. Here's the first one after I torqued it, removed it, torqued again, then sectioned.



I turned the nut until it just started to interfere, marked with a sharpie, then torqued. Both times, the wrench clicked at 1/2 flat of additional turn. Again, this is with 3003 1/4" tubing provided by Vans for the tank vent lines.
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  #5  
Old 07-24-2016, 08:27 PM
BillL BillL is offline
 
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Default Good Research Work

You did your homework. Tested and verified. I did the same thing. Keep it up and you will have a well built plane.
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Old 07-24-2016, 08:28 PM
rapid_ascent rapid_ascent is offline
 
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I measured my crowsfoot wrenches and made a spreadsheet with the corrected values. I think the calculation is in AC43.13. I know a lot of people do the 90 degree thing but I don't think its technically correct. It may be close and good enough though.
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Old 07-25-2016, 05:57 AM
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Check on Amazon. I was able to find a set of 1/4" drive crow's foot. If I recall, the set wasn't that expensive.
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Old 07-25-2016, 07:45 AM
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Quote:
Originally Posted by rapid_ascent View Post
I measured my crowsfoot wrenches and made a spreadsheet with the corrected values. I think the calculation is in AC43.13. I know a lot of people do the 90 degree thing but I don't think its technically correct. It may be close and good enough though.
It IS correct. At 90 degrees, the correct torque is unchanged from the specified value.

http://www.dmctools.com/Products/tor...on_charts.html
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Old 07-25-2016, 08:20 AM
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Quote:
Originally Posted by spaceflightmeow View Post
I got a 3/8 to 1/4 adapter and a 3/8 crows foot set, installed the crowfoot at 90 deg to the torque wrench...

Just in case anyone misinterprets... This photo does *not* show the crows foot at 90 degrees to the wrench.
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Old 07-25-2016, 11:26 PM
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Quote:
Originally Posted by Snowflake View Post
Just in case anyone misinterprets... This photo does *not* show the crows foot at 90 degrees to the wrench.
I'm embarassed to admit that I thought the orientation shown in the picture is 90 degrees. Then again I didn't look too closely, since there was a bit of wobble to the wrench thanks to the 1/4" to 3/8" adapter.
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