torque wrench). This establishes a specific and initial level of clamping force. Final tightening takes place by continuing to rotate the bolt head by a specified number of degrees. This method, developed by OEM engineers, theoretically eliminates the variable encountered with regard to thread friction. Engineering research has determined that by continuing to tighten the bolt by a certain number of degrees stretches the bolt into its desired range of elasticity for optimum clamping force.
Degree tightening can be accomplished by several different approaches, including placing a dot on the bolt head and observing how far the bolt head is rotated (for example, by 45 degrees, 90 degrees, etc.). This is a crude method, because it relies on your estimation of degree travel. An inexpensive tool that aids in angle tightening is a small degree wheel that is attached to a wrench. The wheel features degree increments and an adjustable needle to establish your zero mark and is observed as the bolt is rotated. The downside is that this requires using your torque wrench for initial tightening, setting the torque wrench aside, grabbing a wrench that’s equipped with the degree wheel, and continuing to tighten, while carefully observing the travel.
Another approach involves the use of a digital combination torque/angle wrench. This eliminates the need to switch tools in midstream. By pressing a button, you choose your torque format (ft-lbs or Nm) and your torque value (let’s say 35 ft-lbs for example). When the selected torque value is approached, the tool begins to beep and/or LED lights illuminate to let you know that you’re getting close. After the selected value is reached, the tool provides an audible alert, as well as the illumination of a final red light and a vibration in the tool handle (the types of alerts may vary among tool brands and models).
After the bolt is torqued, you simply press another button to switch to the angle mode, select the degree, and continue to tighten. The same alerts take place during the angle tightening phase. Depending on the tool model, you can even ratchet the tool during angle tightening without losing the angle reference (Snap-on’s TechAngle wrench is an example of this). A number of leading precision tool makers now offer these digital wrenches, including Snap-on, Mac, and others. Granted, they’re a bit pricey, but they work well and eliminate the need to use multiple tools. If you’re using performance aftermarket connecting rods and high-performance rod bolts, a torque-plus-angle approach is not required.
A sonic thickness gauge uses frequency bounce-back signals (similar to sonar) to measure material thickness. A thickness gauge is most commonly used to measure an engine block’s cylinder wall thickness, prior to overboring, to determine existing wall thickness and to make sure that no areas of a cylinder wall are too thin after the cylinder is bored. Potential thin areas include those adjacent to cooling passages. The sonic gauge is first set up using a checking standard, which is a sample piece of metal that is similar to that of the engine block (since iron castings can vary depending on the makeup of the iron). Some gauge kits will include sample standards of a marked thickness. The gauge is calibrated using the appropriate sample. The gauge probe is then lightly coated with a special grease that promotes a good signal. The probe is then put into contact with the cylinder wall, while monitoring the thickness readout. Cylinder walls should be checked from top to bottom at various clock positions, making note of the thinnest reading. Minimum acceptable cylinder wall thickness may vary depending on the specific type of engine block, but generally speaking, a final minimum of about .200 inch should be acceptable. If a specific block is specified for a minimum of, say, .220 inch, and the cylinder wall’s thinnest area currently measures .223 inch, for example, this tells you that a maximum of .003 inch should be removed during boring and honing. A cylinder wall that is considered too thin may be a candidate for sleeving.
After calibrating the sonic checker for the type of block material (some sonic checkers include sample standards of various iron compositions; if not, a section of accessible and easy-to-measure area of the block should be measured with a mic or caliper to calibrate the tool), the tool’s probe is placed against the cylinder wall, with a light coating of supplied grease that permits accurate measurement.
Cylinder walls should be measured for thickness at top, halfway down the bore, and bottom, at a variety of clock positions. Although engine block designs vary in terms of cylinder wall thickness, generally speaking, a minimum of about .200 inch should be acceptable.
The use of a torque wrench allows us to apply a specific amount of rotational force (torque) to a bolt or nut. Torque wrenches are available that provide adjustments in formats including ounce-inch, foot-pounds (ft-lbs), inch-pounds (in-bs), or Newton-meters (Nm). Torque wrenches are available in various designs, including flex-bar style (sometimes called a scale type), dial indicator style, and the common micrometer style (often referred to as a “click” style), as well as digital styles.
With regard to the “click” type micrometer style, “release” models are also available that release upon reaching the preset torque (preventing overtightening), but may not provide an audible click. The release/click type wrench is adjusted by means of a micrometer scale on the handle.
If the torque wrench releases momentarily and/or clicks, this is referred to as a “signal” type. The “indicator” type refers to the visual display units, such as the flex bar or dial indicator style. Newer digital torque wrenches may provide an audible “beep” signal when the setting has been reached, and some may feature both a beep and a vibration when the adjusted level has been reached. The grip vibration feature is helpful in a noisy shop environment. Admittedly, this can be somewhat confusing, since there are so many different types available.
Example of a digital torque/angle wrench. The tool shown here is a Snap-on brand, but other torque wrench manufacturers are also now offering similar technology. Torque is monitored visually via a display window, and an audible beep sounds when the desired torque is achieved. Other models feature a series of green LED lights to alert you when you are approaching the target torque value, with a red light illuminating when the target is finally achieved. A torque/angle wrench allows you to both tighten by torque value and to rotate a fastener by monitoring the tightening angle. Using the Snap-on Tech Angle wrench as an example, press a mode button to enter the torque mode and press the value button until the desired torque is displayed.
Metric scale torque wrenches are available in Newton meters (Nm), meter kilograms (mKg), and centimeter kilograms (cmKg), with Nm being the more common scale. Many torque wrenches provide dual scales for reading in either English or metric formats (for example, a dual scale may offer both ft-lbs and Nm).
Torque wrenches are precision instruments and should be handled as such. Care and storage of a torque wrench is critical in terms of maintaining calibration. Any adjustable torque wrench (the commonly used micrometer-handled click type, for example) should be set at its lowest torque reading when not in use. This is something that many technicians commonly forget. If left stored at a high-torque setting, the calibration may be affected over a long term. When you’re done with the wrench, readjust it to the minimum setting before storing it in the toolbox.
By entering the angle mode, you set the desired angle. When the set angle is achieved, the wrench alerts you via a beep and a vibration in the grip. This is a handy feature for applications where you need to meet OEM torque-plus-angle tightening.
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