Torque wrench

I would suggest you take a look at Ebay. CDI(snap on owned) and other American made 3/4 dial style torque wrenches can be had for less than $100.

Good Luck.

The quick answer is buy a geared torque multiplier from Snap-On. BIG $$$. Or a 3/4 drive dedicated torque wrench. Also BIG $$$. Unless you are "in the business", those actions are not practical.

If I were you, I would fabricate an extension and use a standard 150 lb-ft torque wrench which you may already have. The extension should be the same length as the torque wrench (between the midpoint of the hand grip to the square drive centerline). The extension simply extends the distance between your grip and the bolt you are trying to tighten...beyond what is available with the torque wrench alone. If that distance is now twice what it normally would be, 138 lb-ft on the torque wrench equals to 275 lb-ft on the fastener...a 2:1 increase.

You could make such an extension from a sturdy steel rod with an old socket welded on one end to accept the square drive of your torque wrench (likely 1/2"). A square drive adapter could be welded on the other end to mate with the drive of the socket that engages the head bolts.

A relatively inexpensive solution IMO.

Rod

The torque (or twisting moment) applied to anything is determined by an applied force acting through a radial distance. Say you have a torque wrench that is one foot long from the center of the hand grip to the centerline of the square drive. That wrench will indicate a torque of 50 lb-ft when a force of fifty pounds is applied by your hand: 50 lb X 1 ft = 50 lb-ft. If that wrench were two feet long instead, that same applied 50 lb would result in an applied torque at the end of 100 lb-ft (and registered as such by the wrench).

You are correct in suggesting that for twice the length, you can achieve the same torque with half the applied force. I guess what I am trying to say is that if you apply the same force through twice the distance, you will get twice the torque at the end. In the 275 lb-ft example, the torque the wrench will see (and indicate) will be 138 lb-ft at some force applied at the handle. The torque seen by the bolt at the same time will be twice that (275 lb-ft) since it is twice the radial distance from the same applied force as the wrench square drive is. In other words, the torque that is being measured by the wrench is not the same as that being applied to the bolt.

I believe this is a correct analysis but must confess that I have never actually tried it. It's the same principle as being able to twist off a small bolt a lot easier with a long wrench than a short one.

Rod

Yes, you are correct that the wrench measures torque AT THE HEAD. In the 275 lb-ft example the wrench is, indeed, measuring the torque at the head - 138 lb-ft. However, the torque applied to the bolt is NOT the same as being measured by the wrench. It is actually twice that indicated by the wrench. This is due to the fact that the distance from your hand to the bolt is twice the distance from your hand to the head of the wrench.

This would be true for all types of torque wrenches; beam style, click type or dial type. When you add such an extension, the torque being applied TO THE BOLT is NOT the same as that being measured by the wrench. The user must calculate the actual torque by the unique dimensions involved. In the example, the "cheater" was the same length as the wrench itself. That resulted in a 2:1 increase over the wrench reading. If the "cheater" was twice as long as the wrench, the torque on the bolt would be three times that being indicated (measured) by the wrench.

Skinner is correct; there can all kinds of odd shaped extensions (or adapters) to gain access to fasteners that you can't get the head of the torque wrench on. If the math is done correctly, the wrench can be used quite nicely to obtain the proper torque. The same principles apply. Check out the link for a more authoritative analysis. It is a page from one of my Snap-On torque wrench manuals (pdf file).

Rod

• Torque Extensions

A shop I was working in had the same question, we asked the Snap On man, when he came in about using extensions on torque wrenches. He went into a lot of doubletalk trying to discourage us, and trying to sell us a torque wrench. I think he was talking about using crow foot wrenches at the time.

I thought Snap On had something to do with this question.

The torque wrench is calibrated for the length of the handle. Change the length of the handle=change the calibration...

Cool. Something to file away in the brain for when I need it.