Bolts are designed to tighten objects together. Each bolt has specific tolerance limits before failure. This level of tolerance is determined by the material such as make-up, width, depth and size of a bolt. Too much stress on a bolt will cause it to break. The pressure placed on a bolt is called torque. Each bolt has a specific torque capacity that defines how much pressure it can handle.
Break the pressure of a bolt represented in a formula called pounds per square inch (PSI). Each bolt is designed to support a specific torque tolerance in the PSI before it will fail. This is identified as the pressure of one pound of force placed one inch above the area of a bolt.
There are publicly available specifications charts that document the PSI capability of bolts. These specifications are based on bolt material, number of threads, and overall size. The figures should be used as a guide for an engineer to ensure over-tightening does not occur.
A torque wrench is a special tool designed to measure PSI located on screws or bolts. This wrench has special springs that do not allow the bolts to be coated. The torque wrench operator sets the pressure before the bolts. When torque capacity is reached, the wrench prevents the operator from applying pressure to the bolt.
A car engine is a precision piece of mechanical engineering. There are hundreds of bolts in the engine of a car. Many of these bolts have capacity requirements that vary depending on their location in the engine. Precision tightening is usually needed in the areas of heads, crank, intake and drive. These parts get the most stress during normal operation. A mechanic will use a torque wrench to tighten critical areas of an engine.
Head bolts are the bolts that hold the heads of an engine. These bolts ensure the heads stay secure when the piston explodes against the wheel cylinders. Each car has a specific torque capacity for the head bolts of an engine. This specification is based on the size of the motor and bolts used for tightening.
The mounting bolts are used as a unit for attaching wheels to a car. These ears are designed to ensure the wheels stay securely attached to the car. The mounting bolts have a certain torque tolerance depending on the wheel size and number of knobs. Once the wheels are replaced it is important to check the torque is set. This reduces the long-term stress of the fastening bolts. Most cars require a minimum of 50 foot pounds of PSI.
- Each bolt has specific tolerance limits before failure.