Torque Wrenches - my answer... (Fifield, Douglas)

[SJ]

I think we understand the general theory by now. The problem lies in the
data details.

The best way to illustrate this problem would be with an example using real
numbers.
Tell us what the the torque on the crank bolt should be. Use your formula,
and whatever numbers you have available. Just give us the primary source for
any of your data.

I'll help you out.
Length of 2079 tool = L2079 = 1.0 ft (from a lister that has the tool, I'm
tracking down this number)
Length of the torque wrench = LT = 1.46 ft (I measured my torque wrench,
Sears Craftsman Digitork)
Setting for torque wrench = TW = 258 ft lbs (Bentley 5000S 84-88, pg 13.13)

Assume that all the tools will be in line perfectly so we can eliminate the
alignment complications from the discussion.

Does this sound like a setup? :-)     It is, but this is the best way to
illustrate the problem. Go along with me.

Interesting Footnote:
Bentley 5000S 84-88, pg 13.13 >>> "..apply corrosion inhibitor AMV 186 011
02 to top threads and contact surface of bolt head."

pg 13.18 >> Turbo Diesel > "...258 ft lbs . . .coat threads and contact
surface of bolt head with Loctite 573 or equivalent."
No direct reference to tool 2079. Warning says to see pg 13.16. Nothing
there of importance. Showing how to use tool 2079 is on pg 13.15. I'll
assume this is a typo error in the Bentley.
Loctite 573 Gasketing Product
Fills gaps up to 0.1 mm. Slow cure. Easy disassembly. High resistance to
loads and vibrations.
  a.. Medium strength, bright green colour

  b.. Applications:
  For sealing rigid flange faces on transmissions and engine casings,
differential housing covers, bearing caps, etc.. Fills gaps up to 0.1mm max.
Hmmmm . . .seems using loctite is incorrect, unless you have a diesel.


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q


> From: Gregory Megara <megara at mac.com>
> Subject: Re: Torque Wrenches - my answer... (Fifield, Douglas)
>
> Yes, I agree, though there are a few caveats. I have a civil engineering
background, and being in construction, I have been around a few torque
wrenches.
>
> Doug has it correct but I'll make it simpler:
>
> Torque is Force x Length of lever arm. So, to figure the torque on the
crank bolt can be done with the derived equation:
>
> Needed Torque on the crank bolt = NT
> Length of the torque wrench = LT
> Length of 2079 tool = L2079
> Setting for torque wrench = TW
>
> TW = (NT * LT) / (LT + L2079)
>
> The problem comes when the torque wrench and the 2079 tool are not in line
with each other and that the crank bolt's axis isn't running perpindicular
through this whole torquing action which will reduce calculated torque on
the crank bolt. But torquing isn't something that can be exacted to the
letter in practice. Whatever the NT is in the Bentley manual, there is sure
to be a fair amount of leeway around that.
>
> --Greg