The Importance of Proper Supercharger Belt Tensioning

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. 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 designed tension on the belt, and the addition of manual belt tensioners and the use of non-stock belt lengths 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. Belt lengths must be chosen with care (see the Belt Length Recommendation Chart on our home page), and manual tensioners should be adjusted with caution.

2. Know How to Read Your Belt Tensioner. The belt tensioner used by Ford in the supercharger drive system has a convenient indicator to show when the belt is properly tensioned. The indicator is comprised of a pair of raised ¼”-long pads on the tensioner housing and a corresponding raised rib on the tensioner arm. 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 centered between the high and low pad on the tensioner housing. Variations of +/- 1/16” are considered acceptable.
 
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 an aftermarket supercharger adds significantly to the belt load because these high-performance blowers typically take more power to drive them. In these applications, extra care should be used to maintain proper belt tension, and in extreme cases, the use of heavy-duty double-bearing idler pulleys like our Metco Motorsports 90mm Double-Bearing Idler Pulley should be considered. 

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.  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 more pliable and the noise diminishes.  In this case, the solution is to replace the belt. 

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 should be obvious – there should be discernable drag, unevenness, or wobble evident in the faulty component.

If necessary, the bearings used in Metco Motorsports pulleys can be removed and replaced (in most instances).  The part number for the appropriate bearing is printed on the seal of the bearing, and these bearings (or equivalents) can be sourced from most parts stores.  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 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 bracket, and (if necessary) idler pulleys can be spaced forward by adding a 16mm flat washer behind the pulley.

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 Goodyear Gatorback belt and the Gates Micro-V Greenstripe to be the longest lasting and the most noise-resistant.  Please see our Belt Length Recommendation chart, linked from the right side of our Home page, for the appropriate belt for your application.