Belt Knowledge: A Gripping Tale!

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By Courtney Evans  2 wrench difficulty 2money

Worn Serpentine Belt

Worn Serpentine Belt

Here’s yet another one of those unsung heroes residing in your engine bay. Your drive belts. Let’s talk about belts, shall we? Sometimes they have to screech and squeal before we’ll take notice. That noise is usually the last sign that your belt will give you before it breaks. Sometimes an automotive belt failure will cause a small temporary inconvenience, such as when your steering becomes rock hard because your power steering pump isn’t being turned or it can be much more serious with your warning lights flashing because your alternator isn’t being turned. And in this case, your car will eventually shut off altogether. In either case, it is a serious matter. Your engine cannot run properly without these belts

What they do
Your engine’s drive belts basically “drive” accessories that are either bolted to or hung via brackets to your engine block. What accessories am I referring to? How about that steering pump I mentioned above? Drive belts also turn that little electric generator called an alternator. They also “give life” to your air conditioner’s compressor. In some cases a drive belt might be responsible to turning a cooling fan or even your water pump. All of these devices are essentially powered by the turning force of your engine via a belt of some kind. Drive belts are critical to most secondary engine systems.

Types of Belts
There are several different types of belts that are used on automobiles and motorcycles. We’ll discuss the serpentine, the V-belt, and the toothed V-belts.

The serpentine belt is the most common type of belt used on most cars and trucks. These belts are named “serpentine” because, you guessed it, they are long and their routing through accessories is “snake-like”. This type of belt usually powers a lot of accessories. They were designed to save space by connecting most, if not all of the accessories on the same plane, thereby eliminating the need to stack or stagger the accessories behind or in front of one another. A serpentine belt usually is ribbed on one side and flat on the other. This helps the belt stay in place. Typically, the ribbed side comes in contact with the ribbed pulley of an accessory such as your alternator. The flat side comes in contact with a smooth pulley such as an idler pulley which we’ll discuss below. All belts are important, however I’m sure you can see how important this type of belt is because it may provide power to all of your engines accessories!

The V-belt is still used in modern automobiles. It is called a V-belt because its cross section view resembles the letter V. V-belts typically are used to power a single accessory such as your vehicle’s air conditioning compressor. They are rather simple and fit into a V-shaped pulley. Sometimes they are used in pairs on trucks or other powerful vehicles.

The toothed V-belt is used in high torque applications. Torque is essentially “turning force”. They are also used on powerful engines and on motorcycles. This type of belt has teeth that fit into the grooves of a toothed pulley.

Pulleys basically allow a belt to change direction as it routes to another accessory. All belts must operate under a certain amount of tension or tightness to properly turn an accessory without slipping. How is tension maintained? With an idler/tensioner pulley of course! This type of pulley is attached to a large and powerful spring or a strut type system. These pulleys create tension on the belt by pushing down on the belt so that it tightens. This causes tension across the entire length of the belt, allowing it to “grip” the accessory pulleys. This same thing would happen if you were to push down on a belt at the point where your hand is mid-way between two pulleys or accessories. Maintaining your pulleys is just as important as maintaining your belts.

Common causes of failure
Belts usually fail because they are old, brittle, or rotted. They are very durable; however engine heat is usually not kind to rubber and plastic components in an engine bay. How do you check your belts? Well, if you have a multi-ribbed belt such as a serpentine belt, look for missing chunks of rubber. Make sure there are no gaps between the ribs of the belt. For V-belts, look at the side walls of the belt. It should not be shiny or glazed. This indicates that the belt is slipping and is probably not under the correct amount of tension.

Another cause of drive belt failure is faulty pulleys. They should spin smoothly and shouldn’t wobble at all. The pulley should not have any grease coming out of it. If it does, the ball bearing seal might be broken. Ball bearings work better with proper lubricant. Without it, a catastrophic pulley failure is imminent and it should be replaced sooner rather than later. The pulley should not be able to move from front to back and should not “slide” on its axle.

Idler/tensioner pulleys should provide the right amount of tension on the belt for the system to operate properly. There is normally a tension indicator on the idler and it should be close to midpoint. It should not be on the “loose” part of the indicator. This means that the belt has stretched and should be replaced.

Changing your belts
The first step to properly change your belts is to make sure that you can put the new belt on properly. Usually there is a sticker with a diagram of the belt routing path through the accessories. Look for this and make sure that you understand the diagram. If you’re not lucky enough to have a diagram, get a piece of paper and pen and draw a diagram of your own. Label the accessories with letters such as “A” for alternator and “C” for compressor. This will help identify the accessories and keep the proper orientation.

Next, you need to find your idler/tensioner pulley. If there is only one pulley, obviously this is it. What you have to do is apply opposite force to the pulley. You do this by inserting a ratchet or breaker bar into the square hole in the pulley. Sometimes this hole may not be a square as is the case for many German cars. These cars may have a star shaped hole in the center of the pulley, thus requiring the fitting of a torx bit to your ratchet or breaker bar. So, if the pulley is pushing in one direction, you need to pull in the opposite direction. When you do this you should feel a gradual, but smooth release of tension on the pulley. Push or pull the idler pulley until it stops. At this point you will see that the belt is quite loose. Hold the breaker bar or ratchet with one hand and remove the belt with the other. Once the belt is removed off the idler pulley, you can slowly release the opposing tension that you applied to the pulley. Continue to remove the belt from all of the other accessories.

If there is no idler pulley, as in the case of most V-belts, you simply loosen one of the accessories. Most times, it will be your alternator. If you loosen the right bolt, the alternator will just swing on its axis. Once you move it in the right direction, the tension on the belt will decrease and you can simply take the belt off. If you have more than one belt, one of them may need to be removed first to facilitate removal of the other.

When you have the belts off, take a look at the integrity of your pulleys. If a pulley is bad or if you know it has lots of miles on it, you should just replace it as well.

To put your belt back on, take a look at the routing of the belt using the diagram sticker or the diagram that you drew. Remember, the ribbed side of the belt is usually in contact with a ribbed accessory pulley and the smooth side needs to be in contact with the smooth side of your idler/tensioner pulley. Snake the belt around as many accessories as possible. Make sure that the ribs on the belt fit into the rib on the pulleys. It should rest completely flat in the pulley. Now you need to either push or pull the idler pulley in the same manner you used to remove the belt. Push or pull with one hand and put the belt on with the other. Sometimes another pair of hands comes in handy and makes the job easier. Once the belt is in place, slowly release the opposing tension on the idler/tensioner pulley.

For the V-belt, just put the belt back on; apply tension to the alternator using a breaker or pry bar. Then tighten the bolt that you loosened during removal.

How often should you change your belts?
Well, the correct answer is for you to check your owner’s or service manual since vehicle usage conditions vary so widely. I would definitely change most belts every 50,000 miles. If your climate and driving conditions are harsh, change your belts more often.

Changing your engine’s drive belts is relatively easy. Most problems occur while trying to gain access to the belts. Sometimes you have to change them from above the engine and sometimes from below. If you complete this task yourself, you can definitely save a lot of money. The more you do it, the easier it gets. This is a task that you can complete in an hour or two on Saturday morning.

We’ve all heard that horrible screeching sound of belts slipping. Save your ears and mine by properly maintaining your drive belts.





  • By Edwin 08 Aug 2013

    This is an excellent article and very informative for the Do it yourself home mechanic and auto owner. Even for those who are not very mechanically inclined but may know someone that can help them to carry out the task. Very well written and clear.

  • By Saving Real Money by Doing-It-Yourself. Really? 11 Mar 2014

    [...] Changing Your Serpentine Belt ($90-450)-  This procedure does require some tools.  Mainly a wrench and a ratchet with socket. Depending on your vehicle, you may need to get underneath the vehicle.  You can get a new belt at your local auto parts store.  See Belt Knowledge:  A Gripping Tale! [...]

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