There are a number of automotive fasteners that require accurate torque while they’re being tightened during assembly. Common ones include cylinder head bolts, ring gear bolts, and front wheel unit bearing bolts. These assemblies are designed to be clamped under a certain pressure using the fastener. Too loose a torque can result in poor sealing or retention of the assembly. Too tight a torque can overstress and damage fasteners or other parts. This can lead to reduced life of the assembly.
Snap-on (www.snapon.com) recently released a document detailing proper use and maintenance procedures for torque wrenches to ensure their readings remain consistent and accurate. A torque wrench is a precision tool, so the specific practices described here can help ensure it delivers the proper readings you need.
Additionally, when torquing fasteners, some are specified to be tightened with lubricant applied and some without. Other fasteners may be spec’d to be tightened in stages or with tighten/release cycles. In general, a mechanical torque wrench is designed to operate accurately in a range from 20 to 100 percent of its full-scale torque rating. An electronic one can typically operate accurately in a range from 10 to 100 percent of full scale. You should never exceed the 100 rating. To maintain torque accuracy, only use accessories or handle extensions as allowed by the wrench instructions.