Tool of the Month

People who work on cars are sometimes asked, "What is your favorite tool?" A better question is, "What is the most important tool?" My answer is a torque wrench. Tool collections usually begin with a variety of wrenches, pliers, screwdrivers, hammers, feeler gauges and other simple items. With them, an enthusiast can disassemble most components of a car, make adjustments and put many things back together. But reassembling the more sensitive components-for example, almost any part of the engine or even properly mounting a wheel- requires a torque wrench. It ensures that fasteners apply the correct clamping force to the components they hold, neither loosening over time nor damaging parts or the fasteners themselves by over tightening. A careful mechanic is useless without one.

Most enthusiasts get by with a 1/2-in. drive torque wrench, typically covering a range from about 20 to 150 ft-lb, but a complete tool collection has both large and small torque wrenches. Many smaller fasteners' torque specs, though usually ignored, are just as important. For example, after very carefully manually tightening his cam cover nuts through the many repetitions of a large cam test, a friend was surprised to find several of the cam cover studs beginning to pull out of the aluminum head. Other small fasteners may be for rubber mounts that require just the right amount of tension to work properly. Bottom line, every fastener on a car is torqued precisely at the factory, for a reason. Working on a car correctly requires that these specs be followed. An inch-pound torque wrench is a necessity.

I recently discovered Precision Instruments. From its founding in 1938 until 2003, Precision Instruments' only customer was Snap-on Tools, for which it invented, patented and produced a variety of torque wrenches. Snap-on decided to change suppliers in 2002, and Precision Instruments invented itself as a marketing entity in order to continue in business, selling the same products and supporting users of its products already in the field.

The mechanism of most click wrenches releases with a fixed amount of travel. A coil spring is preloaded to determine the load at the point release occurs. The spring will sag if left preloaded for any length of time, ruining the wrench's calibration, so the wrench must be adjusted to the minimum setting after every use.