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. Bearing Deflection is Part of Bearing Design. The sealed bearings used in OEM idler pulleys and in aftermarket pulleys are of a common design. This bearing design is the result of countless hours and dollars spent on engineering research to ensure that these bearings last for many thousands of miles. Some users complain of a perceived ‘wobble’ in the bearing at rest, but this deflection is the result of a designed .015” clearance to allow for heat expansion. Idler pulleys are subjected to speeds in excess of 20,000 RPM, and if no clearance existed when the pulley was at rest, the bearings would quickly seize as speeds and heat increased.

4. 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.