Manual Torque Formulas

  • WyattsRide
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22 Jan 2011 09:17 #2995 by WyattsRide
Manual Torque Formulas was created by WyattsRide
I read this over at RL and thought it might be a good topic to save here. Thanks to the guys at RL (and here) for their help.

To determine the length of the breaker bar on a nut (such as the rear axle) and applying your weight (standing on the bar and not holding onto anything) to get a certain Torque, without the use of a Torque wrench, the following formulas can be used.

T= Torque (ft/lb)
W= Weight (lb)
L = Length (ft)

Example 1: You know T required (330 ft/lb) and your W (200 lb). Where on the breaker bar (BB) do you apply your weight?

L = T / W or 330 ft/lb / 200 lb = 1.65 ft
or 19.8 inches from the center of the socket.

Example 2: You know T required (330 ft/lb) and max length of the BB (1.65 ft). How much weight do you need to get the correct T?

W = T / L or 330 ft/lb / 1.65 ft = 200 lb

Example 3: You know max length of the BB (1.65 ft) and your W (200 lb). What is the Torque you can apply?

T = L x W or 1.65 ft x 200 lb = 330 ft/lb

max length of the BB can also be any point (from the center of the socket) or length on an infinite size bar.

I hope I wrote this out correctly. Let me know if I didn't. :cool:

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22 Jan 2011 13:11 #2997 by 928mac
Replied by 928mac on topic Manual Torque Formulas
Very interesting.

Stan should something like this be copied into the tech tips and should we just leave it here

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22 Jan 2011 13:35 #2999 by srshaw3
Replied by srshaw3 on topic Manual Torque Formulas
Looks like a good tip to list, so my vote is tech tips.

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22 Jan 2011 16:58 #3000 by the flying scotsman
Replied by the flying scotsman on topic Manual Torque Formulas
May be a good idea to look up some engineering manuals and verify before locking in to tech tips.

No offense to the OP, just being careful.

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23 Jan 2011 13:29 #3012 by WyattsRide
Replied by WyattsRide on topic Manual Torque Formulas
Not sure if I like my title. How about "Manual Torque formulas"?

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23 Jan 2011 17:11 #3013 by 928mac
Replied by 928mac on topic Manual Torque Formulas

Not sure if I like my title. How about "Manual Torque formulas"?


Ok I changed it for you

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31 Jan 2011 01:17 #3183 by Kiln_Red
Replied by Kiln_Red on topic Manual Torque Formulas
Just to elaborate on this subject a little, I know that these formulas work first hand. I used to use the same math back before I ever owned a torque wrench. In most situations, I would angle torque if that was an option. I still angle torque as a first option, and torque to spec only when there is no other way. Torque to spec is alright for tightening lug nuts. Angle torque bearing caps and head nuts/bolts.

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31 Jan 2011 18:50 #3222 by WyattsRide
Replied by WyattsRide on topic Manual Torque Formulas

Just to elaborate on this subject a little, I know that these formulas work first hand. I used to use the same math back before I ever owned a torque wrench. In most situations, I would angle torque if that was an option. I still angle torque as a first option, and torque to spec only when there is no other way. Torque to spec is alright for tightening lug nuts. Angle torque bearing caps and head nuts/bolts.


Austin,
Just so I understand.

Torque to spec is using the formulas above.
Angle Torque is using the wrenches.

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06 Feb 2011 11:51 #3312 by Kiln_Red
Replied by Kiln_Red on topic Manual Torque Formulas
Torque to spec, as some people refer to it, is a specific value that you're trying to torque to. Angle torquing is where you turn a nut/bolt in X amount of degrees. To do this, you simply mark the hardware in a fashion that allows you to see how much you're turning it in degrees.

For torque to spec, you must use either a torque wrench or your method originally posted. Of course, you must lubricate the threads and it's advised to use new hardware every time as well. Usually it's okay to use just new nuts and washers where necessary, in my opinion. On torque-to-yield hardware, it's recommended to also change the studs however. Angle torquing is more precise, particularly where greater torquing is necessary. That's why you see it used more for critical engine components such as cylinder heads and stud girdles for the crankshaft main bearings.

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