Automobiles have operated with power transmission belting for several centuries. The earliest belts used within engines were flat which ran along flat pulleys. Though few know it, such early engine drive belt systems had hemp and cotton rope that worked in unison with V-grooved pulleys to minimize tension on the belt. In fact, the flat, V-grooved synchronous belts are still used in power transmissions to this day. Engine drive belts are a low-cost and flexible design that can be installed with ease. Obtaining replacement parts for belt drive systems is surprisingly easy. Let’s dive into the basics of engine drive belt systems to develop a better understanding of how they are engineered and the manner in which they power automobiles.

The Merits of Belt Drives

Belt drives are favorable compared to gear drives as they extend across more space between shafts. Furthermore, belt drives have a superior design compared to gear drives as belt drives are designed much more simply. Belt drives are also superior in that they have comparably elastic belts while gear systems are quite stiff. This enhanced flexibility boosts the shock absorption through damping that proves quite helpful when torque quickly changes.

The Different Types of Belts Within Engines

Serpentine Belts

Serpentine belts are the type most commonly used in modern-day vehicles. Pop the hood of your vehicle, and you are nearly guaranteed to find one of these belts, assuming your vehicle was made in ’90 or later. Serpentine belts are surprisingly easy to change. The belt is positioned in between several different accessories ranging from crank pulleys to idler pulleys and tensioners. If the serpentine belt has significant cracking or if the belt’s grooves are shallower than they should be, it is time for a replacement.

In general, the serpentine belt should be checked at the 60,000 and 90,000-mile marks. If you need to change your vehicle’s serpentine belt, you can do it on your own. Anyone with basic automotive knowledge can easily use a socket to pull on the tensioner pulley to loosen up the belt to remove it from the engine.

Timing Belts

The average vehicle has an interference engine, meaning clearance in between moving parts is limited to the point that there is the potential for them to run into one another. The timing belt connects with both the camshaft and crankshaft to ensure they remain in sync. However, you probably won’t see this belt as it is concealed behind the timing cover. Ignore the timing belt at your own peril. Timing belts will eventually crack just like every other belt. If the timing belt malfunctions or is not replaced prior to the 90,000-mile mark, you might have a costly engine rebuilt project on your hands.


Older automobiles typically have drive belts, also known as V-belts as they have tapered rubber teeth. Though these belts are dated, they have their benefits. The drive belt runs off the crank pulley and moves through one or several accessories within the engine. Some vehicles are equipped with several of these belts for air conditioning, the alternator, power steering, radiator fan, and the water pump. If one of these drive belts is broken, it still might be possible to make it home, yet it will likely squeal along the way and prevent the alternator from charging as it should.

Tension is of the Utmost Importance in the Context of Engine Belts

The tension within the belt drive hinges on the type of belt along with the horsepower and even the drive rpm. More often than not, a method known as force/deflection is used to measure belt drive tension. The addition of a new belt to an engine requires comparably high tension. The logic in boosting the tension at this point is that it will quickly drop soon thereafter amidst the seating-in process. The tension of the drive belt can be tested by pushing down on it in the center along its largest section. If the drive belt depresses more than half an inch, it is loose and requires tightening. If the drive belt does not compress half an inch, it is too tight. Excessive tightness strains the alternator and has the potential to lead to all sorts of problems. If you have automotive knowledge or would like to learn more about automobiles, you can test your engine belts’ tension on your own. However, if you are hesitant to gauge belt tension on your own, don’t hesitate to let a professional mechanic take a look under the hood on your behalf.