Question for the fellow mechs and gearheads – normal torque wrenches everywhere, but where can I find an open end torque spanner with interchangeable (imperial) bits? Something like this ?
They are called ’Crow’s foot’ wrenches and are quite widely available.
One thing to remember is that the torque calibration will only be correct when the Crow’s foot is at 90° to the handle. Otherwise you need to apply a correction for the ratio of lengths from the hand grip to the torque head over the distance to the bolt centre (those distances are the same at 90°).
Or just use a ordinary combination wrench with the round socket on the torque wrench.
That combo won’t work – i need to tighten a nut that has a pipe going through the middle.
Mark_1 wrote:
They are called ’Crow’s foot’ wrenches and are quite widely available.
+1
Spend some time in a shop and notice how little use they make of torque wrenches… If it’s difficult to reach, get a feel for the torque somewhere else and do it that way.
AC43.13 chapter 7 discusses how to correctly torque with an extension – http://www.faa.gov/documentLibrary/media/Advisory_Circular/Chapter_07.pdf
For flared pipe fittings, there is an official torque, but it is much less critical than in load bearing structure as the requirement is just a good seal between the pipe flare and the 100° cone surface on the fitting. I would usually apply a little gasket compound to the thread and tighten to a ‘snug’ fit i.e. one finger pressure on the end of the spanner.
If you’re fitting a Hartzell prop to an engine, then you will need a crow’s foot and an accurate torque wrench.
This is a good guide – http://www.vansaircraft.com/pdf/Torque_Spec_Aluminum_Fittings.pdf
Shorrick_Mk2 wrote:
That combo won’t work – i need to tighten a nut that has a pipe going through the middle.
The round end on the torque wrench and the open end on the nut.
I am just trying to understand the correct procedure for tightening hydraulic line fittings and found this old thread. Comparing the recommended torque values in the document referenced by @Mark_1 the they are nearly twice the values as recommended in the FAA AC43.13-1b table.
There are several other publications that on the other hand prefer a defined amount of turning the nut either based on counting the flats (FFWR, flats following wrench resistance) or simply turning one quarter turn after hand tightening. Actually the turn method makes more sense to me because you want a defined pressure between the flared tube and the fitting which can be described best by a exact movement on the threads. The torque method in my opinion is dependent on factors like friction which can be influenced by lubricants, re-use of the fitting etc.
Understanding that it is vital not to tighten to much causing cracks in the tube or the fitting but also not risking leaks by undertightening I guess this is important to do it right, What practical approach do others recommend?
There are several types of crowsfoot wrenches. If it looks like an open end wrench, which can be slid onto the flats of the hex from the side, it’s the wrong type for a flare nut on plumbing. The correct type of crowsfoot wrench for flare nuts can be found by searching under that term. It will have more than the four internal flats, and have to be slid onto the hex axially along the tube. It should be used with the correct calculations with a torque wrench, to the torque specified in the maintenance manual for the product. AC43.13 torques are for use when no other information is available, and for dry threads.