Vehicle manufacturers specify torque values for certain fasteners. This is to make sure that fasteners are not over- or under-tightened. The torque wrench is used to apply a specified amount of torque to a fastener. The torque angle gauge is used to make sure there is equal tightness of fasteners on a component. The objective of this procedure is to show you how to use a torque angle gauge in conjunction with a torque wrench.
Part 1. Preparation and safety
- Use a torque angle gauge in conjunction with a torque wrench.
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
- Refer to the manufacturer's specifications when tightening fasteners.
- If replacing a fastener, make sure it has the correct tensile value for the task it has to perform.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- Over-tightening a fastener can damage the gasket and the threads.
- Support the head of the torque wrench during its use.
- Vehicle manufacturers specify torque values for certain fasteners. This is to make sure that fasteners are not over- or under-tightened.
- The torque value will be specified in foot-pounds (lb-ft) or Newton-meters (Nm) and is the amount of twisting force applied to a fastener by the torque wrench.
- A foot-pound is described as the amount of twisting force applied to a shaft by a lever one foot long with a weight of one pound placed on the outer end. A torque value of 100lb-ft will be the same as a 100 lb weight placed at the end of a 1-foot-long lever.
- A Newton-meter is described as the amount of twisting force applied to a shaft by a lever one meter long with a force of one Newton applied to the outer end. A torque value of 100Nm will be the same as applying a 100 Newton force to the end of a 1-meter long lever.
- One lb-ft is equal to 1.35 Nm.
- The torque wrench is used to apply a specified amount of torque to a fastener.
- There are various methods used by torque wrenches to indicate that the correct torque has been reached. Some will give an audible signal such as a click or a beep, while others will give a visual signal such as a light or a pin moving or clicking out.
- Make sure the threads are clean before tightening the fastener to a specified torque. Any friction will give an inaccurate reading and will affect the compressive force the fastener will apply to the component.
- Always handle a torque wrench carefully. It is a precision instrument that will lose its calibration if mistreated.
Torque angle gauge
- The torque angle gauge is used to make sure there is equal tightness of fasteners on a component. It is calibrated in degrees.
- Tightening by angle rather than torque removes the error that is produced by friction in the threads.
Torque to yield (also known as torque and turn)
- Some fasteners are designed to be deliberately over-tightened. These bolts are known as "torque to yield" bolts. The fastener is tightened to a specific torque with a torque wrench, then the torque angle gauge is turned a number of degrees.
- When tightened, these fasteners are stretched beyond their elastic limit. So when they are removed, they must be discarded and replaced with new ones.
Part 2: Step-by-step instruction
- Check the specifications
Determine the correct torque value for the bolt or fastener you’re using. This will be in Foot-Pounds or Newton Meters. Also, check the torque angle specifications for the bolt or fastener.
- Tighten the bolt
Tighten the bolt to the specified torque.
- Install the gauge
Install the torque angle gauge over the head of the bolt, and then put the torque wrench on top of the gauge.
- Torque to specifications
Turn the torque wrench the specified number of degrees for that bolt. If the component requires multiple bolts or fasteners, make sure to tighten them all to the same torque value and torque angle.