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Torque Wrench extensions

If, like me you don't have a torque wrench that has the capacity to torque up the Rear hub nuts of the Flywheel gland nut, here is the solution.
You do still need a torque wrench, but only one that is capable of up to 100 lbs.ft. You will also need an appropriate extension.
You can increase the output of a torque wrench by putting an extension between the wrench and the nut in question. Following is an extract from a torque wrench manual:

Before carrying out this process be sure you fully understand the theory. Nuts and bolts incorrectly torque loaded can cause damage or injury.

How adaptors affect torque

To understand why certain types of adapters and extensions change the amount of torque delivered at the bolt head it should be remembered that the amount of torque produced at the bolt is the result of the amount of force applied and the length of the torque wrench plus the length of the extension or adapter. Remember the torque law:

Force x distance = torque.

However, when special accessories are used that add length to the torque wrench, the setting no longer reads true and corrections must be made to compensate for any added length. Adapters or extensions may be used with a torque wrench for many reasons.

  1. To adapt torque wrench to special fittings or applications.
  2. To increase or multiply torque past the capacity of the wrench.
  3. To torque fasteners in hard to reach locations.

How to compute torque

If an adapter is attached to the square drive of a torque wrench, the wrench will not give the actual torque indicated by the setting of the handle. A simple formula however, allows you to figure out what the setting should be to deliver a pre-determined amount of torque at the end of any adapter to the fastener.

Here is the formula:

The letters in the formula have the following meaning.

A = length of torque wrench
B = length of adapter
C = torque wrench setting
D = desired torque at end of extension

Here is a typical problem:
You have an adapter 42" long and you want to acheive a torque at the nut of 256 lbs.ft.
Your torqye wrench is 18" long.
So, using the above letters:

A = length of torque wrench = 18
B = length of adapter = 42
C = torque wrench setting = ?
D = desired torque at end of extension = 256

So, with your 42" extension on your 18" torque wrench, to acheive 256 lb.ft at the nut you need to set your torque wrench to 76.8 lbs.

Here is a general view of the extension made up of a 3/4" breaker bar with an extension bar fitted. I have welded a 1/2" socket 42" from the socket end (indicated by the arrow).

Measure the length of the extension from the centre of the socket square drive to the centre of the torque wrench adapter square drive.

Measure the length of the torque wrench, here measured to the centre of the knurled handle.

One thing to note when operating the wrench is to ensure that the wrench stays inline with the extension.