Tension Wrench Question

**d2dave** · 14th June 2016, 09:33 PM

Fitting a new harmonic balancer to Td5. Bolt tension required is 340 ft lb.

My tension wrench(TW) only goes to 120 ft lb.

I do not wish to go and purchase a bigger TW for one bolt.

Now I know that if I make up a length of steel that I can fit between the TW and the bolt, I can achieve 340 ft lb with my TW.

Does anyone know the formula for working this out.

I have done a lot of googling and every site I find has formulas that include the length of the TW.

I can't see how the length matters. For example, if I put an extension on the handle of my TW, it will not affect the bolt tension, it would just mean that less effort would be required for the same result.

**bee utey** · 14th June 2016, 10:37 PM

Your torque wrench needs a force of X pounds at Y feet to produce a torque of X.Y lb-ft. Say your torque wrench handle is 1.5 ft from the centre of the drive bit to the centre of the handle. You then need a force of 80lb to produce a torque of 120 lb-ft. If you added a cheater handle to triple its length you need 80/3 =26.6 lb instead. But that's not what you need.

Instead of that, you move the drive bit onto an adaptor so that the centre of the torque wrench handle is now 3x that distance from the crank bolt. The same 80lb that makes the wrench read 120 lb-ft now is multiplied by 4.5 ft to produce a torque of 360 lb-ft. Measure the distance of the centre of the torque wrench handle to the drive centre as best you can. Tripling this distance gives you a simple 3x ratio that is easy to calculate but of course any other ratio would work too, just needs more calculating.

**alien** · 14th June 2016, 11:10 PM

I do as you want to Dave.
I add a pipe etc. into the system and do the maths.
The setting usually is around 80ft/lb with my set up after doing the calculating.

Torque Wrench Adapter Extended Equations & Calculator | Engineers Edge

**damienb** · 15th June 2016, 05:46 AM

I just put a digital fishing scale on the end of a breaker bar or cheater pipe and calculate torque/distance to get force. You can make up or buy an extender, but this is easier. Note that any inaccuracies are also multiplied with an extender.

**Gerokent** · 15th June 2016, 03:01 PM

Also, over extending of the max torque setting on your TW will render it U/S for next time you want to use it.

Tombie · 15th June 2016, 04:24 PM

Hire one!

**d2dave** · 15th June 2016, 05:22 PM

Originally Posted by bee utey

You Measure the distance of the centre of the torque wrench handle to the drive centre as best you can.

This is the bit I don't understand. I would have thought that I would only need to measure from the bolt head to the point on the TW where you attach the extension piece.

If I use my TW normally, it makes no difference as to the handle's length.
As I said in my OP. If say I had a crook shoulder and needed 100 ft lb,
I could set the TW at 100 and then put any length of pipe I want over the handle and it would make no difference.

Tombie · 15th June 2016, 05:49 PM

http://www.engineersedge.com/manufac..._extension.htm

Tombie · 15th June 2016, 05:53 PM

In short - to make it easier to reach the torque (say with a dickie fin) extend the bar...

To make it generate higher torque - extend the "socket" from the TWs original position by a multiplying factor (not the handle end)

**bee utey** · 15th June 2016, 06:10 PM

Originally Posted by d2dave

This is the bit I don't understand. I would have thought that I would only need to measure from the bolt head to the point on the TW where you attach the extension piece.

It's really quite simple. If you apply 80 lbs at 1.5 feet from the pivot you will have a torque of 120 lb-ft. If your torque wrench is calibrated correctly it will also read 120 lb-ft. If you apply 80 lbs force at 4.5 feet from the pivot using a 3 ft adaptor, your torque wrench will still read 120 lb-ft but a torque of 80 lb x 4.5 ft = 360 lb-ft will be generated. Now add an extra 1.5ft extension handle to the torque wrench to make it 3 ft long. Put a 40lb force on the handle. Your torque wrench will still read 120 lb-ft but your actual torque will be 40 lb x 6 ft = 240 lb-ft. Moving your hand will affect the desired result quite considerably because the torque wrench calibration only works with its original geometry. In the opposite direction, you can apply your 80 lb force to the pivot of the torque wrench where it is connected to the adaptor. The torque wrench would obviously read zero but you would still be applying a torque of 80lb x 3 ft = 240 lb-ft to the fastener.

You don't have to understand anything other than the basic maths, torque equals force multiplied by distance. A torque wrench scale will let you calculate what force is being applied to the handle only if you know the distance from its pivot. Leaving your hand in the exactly same spot guarantees that the force is the same for any given reading. Then multiply the calculated force by the new distance using the adaptor and you have your new torque. If you borrowed a spring balance you could try the various scenarios and see what I mean. Or just use the spring balance and a lump of pipe.

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