There are two types of drive belts: V-type and Serpentine type. The objective of this procedure is to show you how to inspect and manually adjust engine accessory drive belts.
Part 1. Preparation and safety
- Inspect and manually adjust engine accessory drive belts.
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.
- Never try to inspect belts with the engine running.
- Always make sure that you wear the appropriate personal protection equipment before starting the job. It is very easy to hurt yourself even when the most exhaustive protection measures are taken.
- Always make sure that your work area/environment is as safe as you can make it. Do not use damaged, broken or worn out workshop equipment.
- Always follow the manufacturer's personal safety instructions to prevent damage to the vehicle you are working on.
- 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
- There are two types of drive belts:
A V-type belt has a profile that looks like the photo below, and sits inside a deep v-shaped groove in the pulley wheel. The sides of the V-belt contact the sides of the groove
Serpentine-type belts have a flat profile with a number of grooves running lengthwise along the belt. These grooves are the exact reverse of the grooves in the outer edge of the pulley wheels; they increase the contact surface area, as well as prevent the belt from slipping off the wheel as it rotates.
- Conditions to look for on a drive belt:
Cracks in a belt indicate that it is getting ready to fail and should be replaced.
A belt that has been soaked in oil will not grip properly on the pulleys and will slip. If the oil contamination is severe enough for this to happen, replace the belt.
Glazing is shininess on the surface of the belt, which comes in contact with the pulley. If the belt is very worn, the glazing could be caused by the belt "bottoming-out" (see below), and it should be replaced. If it is not old and worn, glazing could simply indicate that the belt is not tight enough. Tightening the belt may be all that is necessary, depending on how bad the glazing is.
Torn or split belts are unserviceable and should be replaced immediately.
When a V-type belt becomes very worn, the bottom of the V-shape may contact the bottom of the groove in the pulley, preventing the sides of the belt from making good contact with the sides of the pulley groove. This reduced friction causes slippage; a belt worn enough to bottom-out should be replaced.
- Manual belt tension versus automatic belt tension
- Many vehicles require the technician to manually adjust the tension on the belt. Other vehicles have an automatic spring tensioning system. Depending on the system used on the particular vehicle, you should always follow the manufacturer's service instructions.
- There are a number of different types of tension gauges. Follow the operating instructions on the tool. If you don't have a tension gauge, you can estimate the tension by pushing the belt inwards with your hand. If it's correctly tensioned, you should be able to deflect the belt about 1.25 centimeters for each 30cm of belt (half an inch for each foot).
Part 2: Step-by-step instruction
- Inspect and check belt condition
Twist the belt so that you can see the underside of the ‘V’ shape or the ribs on a Serpentine belt. Look for signs of wear and damage. You may need a flashlight to see these clearly. A cracked or glazed or torn belt will need to be replaced.
- Check tension
Check the belt tension by attaching the tension gauge to the longest belt span, and pulling it to measure the tension. Compare your reading to the specifications in the vehicle workshop manual.
- Choose the correct tools
Select the correct wrench to loosen the tension adjustment fastener. This is usually on the Alternator mounting or on a separate idler pulley wheel. You will also need a pry bar, which is a metal bar you can use as a lever to apply tension on the belt.
- Adjust belt tension
Loosen the adjustment fastener, then wedge the pry bar between the alternator and a strong part of the engine and pull in the direction that will apply tension to the belt. Tighten the adjustment fastener.
- Check tension again and readjust if necessary
Check the tension again with the gauge, and if necessary loosen the fastener and adjust the belt again until it is at the correct tension for the vehicle.
- Start the engine
Start the engine and observe the belt to make sure it is properly seated and operating correctly. Stop the engine again and recheck the tension.