Torque Wrench Buyer's Guide

Torque wrench tips for tractor restoration projects

- By Dave Mowitz

Torque wrenches aren't used often in your restoration chores. Brought out sparingly, these specialized ratchets are key to tightening specific fasteners. But often, their lack of common use results in these tools being misunderstood or abused.

For starters, a torque wrench is not just another ratchet wrench. Actually, they should never be used as the primary means of tightening or loosening bolts and nuts.

Value of a Torque Wrench

Why use a torque wrench in the first place, when you could use a simple ratchet wrench to get a fastener down as tight as possible?

First of all, a torque wrench doesn't get a bolt or nut down “tight as possible.” Instead it tightens a fastener to the exact pressure needed for the situation.

For example, overtightening an engine head bolt could “squeeze” the head's gasket, jeopardizing the gasket's ability to form a tight seal.

The proper torque for a fastener is also impacted by the overall length of a bolt, the material of the clamped parts, the presence of a gasket between the two parts, and even the alloy of the bolt itself. Plus, proper torque values take into account the friction between the threads, which is the single biggest variable that affects the relationship between the torque applied to the bolt head and the clamping force. Friction arises from the threads, as well as the rotating bolt face scrubbing along the stationary workpiece.

Overcoming friction can account for as little as a few percent or as much as 50% of the force needed while tightening a fastener. And that means the clamping force can vary widely.

Most torque wrenches are length specific or dependent. This means that holding a wrench at different locations along its handle changes the torque applied to the fastener, even if the wrench is preset.