Understanding Your Blower Drive - Article

The Importance of Proper Supercharger Belt Tension

The serpentine accessory and supercharger drive systems used on modern vehicles have very little in common with the standard V-belt drives to which many of us are accustomed. Here are a few tips that may prove helpful in minimizing belt slippage, maximizing pulley bearing and belt life, and diagnosing problems with serpentine belt drives:

1. Proper Serpentine Belt Tension is Critical.
Serpentine belt systems are designed to operate at a very specific tension, unlike old V-belt systems that run at maximum tension to prevent slippage. Factory serpentine belt tensioners have a carefully-engineered spring mechanism to maintain the necessary tension on the belt, and changes made to the belt or components on the blower drive can lead to improper tension on the belt. Serpentine belts are very susceptible to stretch when over-tensioned, and stretch will lead to slippage and ultimately the failure of the belt. Additionally, the vast majority of bearing failures in stock and aftermarket pulleys can be traced to over-tensioned serpentine belts. If tools are necessary to install your belt, or if pulleys must be removed to get your belt in place, then your belt is too tight. Belt lengths must be chosen with care (see the Belt Length Recommendation Chart, also in our resources section), and manual belt tensioners should generally be avoided. Note that some belt slippage in the supercharger drive is necessary to allow the supercharger and the crank a moment to synchronize, as these two components accelerate and decelerate at very different speeds. A belt that allows no slippage at all, such as a very tight belt or a cog-style belt, will be very hard on parts and offer a very short service life.
2. Know How to Read Your Belt Tensioner.
The belt tensioners used by Dodge, GM, and Ford have convenient indicators to show when the belt is properly tensioned. The indicator is typically comprised of a raised boss cast into the tensioner mount and a corresponding raised rib on the spring-loaded tensioner arm. In most applications, the tensioner indicator is best viewed from the passenger side of the vehicle, and when the belt is properly tensioned the raised rib will appear roughly centered against the raised casting. The tight side of this range is considered ideal for high performance supercharger drives.
3. Changing Pulley Ratios and Using Aftermarket Superchargers Will Make Belt Tension More Critical and May Affect Pulley Choice.
The use of overdrive (smaller) supercharger pulleys and overdrive (larger) crank pulleys will affect belt loads, belt speeds, and the speeds of any accessories that share the supercharger drive belt (like the alternator on the Cobra). Additionally, the use of a larger aftermarket supercharger can add significantly to the belt load because these high-performance blowers may take more power to drive them. In these applications, extra care should be used to maintain proper belt tension to avoid damage to blower drive components, including the sensitive bearings in the supercharger snout. For those operating at very high boost and power levels, it may be necessary to accept that some components in the blower drive may become consumable. We offer our double-bearing idler pulleys for use in these severe applications, which is as durable a pulley as we can manufacture.
4. Diagnosing Belt Noise.
The supercharger drive in high-performance applications is often noisy, and finding the source of the noise is not always easy. We have found that an audible squeak or a chirp that is present upon engine start-up but disappears as the engine warms is often caused by the supercharger belt itself, or possibly a very minor alignment issue. When the engine is cold and the belt is cool and stiff, noise is created as the belt transitions from one pulley to another. As the belt warms, it becomes softer and more pliable and the noise diminishes. In these instances, the most likely solution is to replace the belt, and possibly investigate the alignment of the pulleys on the drive, particularly the grooved pulleys. A noise that is constant or becomes worse as the engine warms is more likely a pulley or an accessory on the supercharger drive. The best method to find the exact source is to simply release tension on the belt and spin each pulley in the supercharger drive by hand. A pulley or an accessory with a failed bearing will be obvious – there should be discernable drag, but unevenness, notchiness, or wobble evident in any component indicates a problem.
We intend for the bearings in our pulleys to last forever in a properly set up system, but if it becomes necessary, the bearings used in Metco Motorsports pulleys can be removed and replaced. We use a 6203-style bearing, which can be purchased directly from us as a service part, or sourced at a parts store local to you. If you choose to source your own bearings, use the highest-quality 6203 bearing you can find. Please feel free to contact us for information about the bearing replacement procedure. If your supercharger belt shows evidence of fraying at the front or rear edge, there is an alignment issue that should be corrected. Typically, most alignment problems involve a grooved pulley in the blower drive, such as an improperly installed supercharger pulley, or (in the case of the Mustang Cobra) an out of alignment alternator pulley. Alternator alignment can be adjusted on the Cobra by grinding the mounting points of the alternator case or bracket, or adding spacers at each mounting point to move it the other way. Idler pulleys can be spaced forward by adding a standard 16mm flat washer behind the pulley. See our Belt Troubleshooting Guide, also in our Resources section, for more details specific to the Mustang Cobra. In all supercharged applications, supercharger belt life will be significantly shorter than the service life for a typical accessory belt. Supercharger belts should be replaced regularly with the highest quality belts available. We have found the Gates Micro-V Greenstripe (HD Fleetrunner series) to be the longest lasting and the most noise-resistant. Avoid entry-level parts store belts, and avoid race belts such as the blue RPM belt, as we have found these RPM belts to be too stiff for OEM-style supercharger drives. Please see our Supercharger Belt Length chart, also in our Resources section, for information on the appropriate belt for your application.