Motorcycle Precision Measurements - Part 5
Torque is the amount of rotational or twisting force that can be exerted by an engine, instrument, or other rotating object. In the English measuring system, the common measurements or specifications are in inch-pounds or foot-pounds. The length in inches indicates the distance from the center of rotation; the force in pounds indicates the pressure exerted at that distance from the center of rotation. In the metric system the specifications are given in kilogram-centimeters or kilogram-meters.
The force exerted by an engine is specified as a given torque at a given rpm of the engine. The force exerted by a fastener is specified in a torque applied to that fastener. A common example of this is a cylinder head that is tightened with all of the head bolts or fasteners applying a retaining force or torque of the same specification. The manufacturer might specify that all head bolts be torqued to 25 foot-pounds. Torques for fastening most components of a vehicle are often specified.
Three common styles of torque wrenches are the dial indicator type, the pre-set click type, and the beam type. Air impact wrenches are also capable of applying high torque. There is usually an adjustment on these for pre-setting the amount of torque desired. Forgetting to adjust this torque will often result in broken bolts or stripped threads. Other wrenches are also designed to apply a certain torque within a given range. A smaller wrench with a short handle will obviously apply lower amounts of torque than the same size wrench with a longer handle, or a larger wrench with a longer handle. Adding some kind of extension to a wrench of a given design destroys the designer's intended torque range for that wrench.
A mechanic needs to calibrate his equipment, care for it, and store it correctly to insure that it will continue to give accurate measurements. For instance, calibrating a 1-inch micrometer is accomplished by closing it until the spindle just touches the anvil, then observing that the reading is zero. Of course, a micrometer should not be stored this way. The anvil should never touch the spindle during storage. Calibration of a pressure gauge is accomplished by measuring it against a known standard, such as a master pressure gauge, to see if both gauges read exactly the same for a given pressure.
Many instruments, such as scales or rules, are not designed to be recalibrated. Therefore, they must be used and stored carefully. This includes lubricating the moving parts where necessary and applying silicone spray or wax to prevent rust on unfinished metal parts. Common sense should be employed when using or storing measuring instruments. They should be used only to do the job that they were designed for. Never substitute a measuring tool for some other device just because it's handy.
It is particularly important to clean measuring tools before returning them to their proper storage place. Clean, dry storage insures more accurate readings. Also, returning them to their proper storage place will insure that you will know where to find them the next time you need them. A special storage cabinet or box is "a must" for a measuring instrument if it is to retain its accuracy. Measuring tools are some of the most expensive equipment a mechanic ever purchases; they should be treated with the proper care. Accurate calibration, careful storage, and proper usage are necessary ingredients to protect your investment.