Troubleshooting Belt Alignment
Troubleshooting Belt Alignment Issues
The serpentine supercharger drive on a performance vehicle is very different than the accessory drive found on every standard vehicle. Instead of connecting engine power with (almost) free-wheeling water pumps, alternators, and power steering pumps, the supercharger drive is tasked with transmitting engine power to the supercharger pulley to spin an air compressor, and this compressor offers significant resistance. The supercharger belt itself is subject to the pulsations of engine rotation, the resistance of the blower, and the vibrations and harmonics in between. This environment is even more brutal in cars with manual transmissions, which subject the blower drive to more sudden and dramatic changes in engine speed and engine load.
Unlike the V-belts of old, serpentine systems are designed to operate at a very specific level of tension. This tension is regulated by the spring-loaded belt tensioner in the blower drive, and the use of modified or manually-adjustable tensioners can put undue stress on the belt and excessive side load on all components on the blower drive. This unnecessary load compromises reliability and dramatically shortens the life of the belt and all components on the drive. Contrary to popular belief, tighter is not better.
When supercharger drives are modified, especially when larger diameter pulleys are added, the blower drive system becomes much more sensitive to belt alignment. In applications like the 2003-2004 Mustang Cobra, the supercharger drive is very complex and is unusually sensitive to improper alignment.
Listed below are the most common causes of belt noise and alignment issues for the Mustang Cobra, but these concepts apply to all serpentine drives, including the Lightning truck, the GT500, the CTS-V and ZL1, and the Hellcat:
1. Improper Belt Length.
A belt that is too long or too short will always create problems. A belt of the improper length will have much shorter service life, but more importantly it will be likely to ‘walk off’ pulleys in the blower drive. By far, a belt that is too short is the most common cause of what is thought to be an alignment issue with pulleys on the drive. We have a belt length chart on our website, or you may also contact us directly. Please note that it is necessary to have details on every pulley on the blower drive in order to calculate the proper length.
2.Failing Belt Tensioner.
The spring-loaded OEM tensioner, particularly in Mustang Cobra and Lightning truck applications, is very prone to flex under load. In all blower drives, the belt moves forward (towards the radiator) when the belt is loaded (under boost). This movement is a function of the rotation of the belt, and this movement of the belt on the pulleys is sometimes mistaken for an alignment issue. In the case of the Cobra and Lightning, the belt pulls the end of the tensioner arm (at the pulley) forward with significant force. In extreme cases, the tensioner arm will flex to the point of catastrophic failure, but more commonly the arm will simply bend and cause the belt to mistrack under all conditions. We always suggest a visual check of the tensioner – peering over the passenger-side fender at the tensioner will reveal if the arm has taken a permanent set with the tensioner pulley angled forward towards the front of the car. Check yours - you may be surprised.
Additionally, we have found that some of the ‘reasonably-priced’ billet tensioners available in the aftermarket can introduce significant alignment issues. In fact, very few of the available aftermarket tensioners actually provide proper tensioner pulley alignment without modifications - always check your installation to confirm proper pulley positioning.
3. Alternator Pulley Alignment
Those familiar with the Mustang Cobra are well aware of the high failure rate of alternators. At nearly 20 years since production, very few Cobras still have the alternator they were born with. Some may have custom aftermarket units, but most have mass-produced rebuilt units, which are often pieced together from piles of alternator shafts, alternator cases, and alternator pulleys from similar Modular applications. The resulting combination of parts can create a situation where the alternator pulley is no longer in perfect alignment with the crank pulley, and the addition of larger crank pulleys (and larger alternator pulleys) make alignment even more critical. It is worth noting that a minor misalignment may not cause any obvious problems, but when a larger crank pulley is added that existing minor alignment issue becomes a problem. Also, be aware of the cheaply-made, knock-off alternator pulleys available in the aftermarket. The Metco Motorsports alternator pulleys are precision-machined as a single assembly to ensure proper belt alignment.
In most cases, you can verify alternator pulley alignment by looking at the relationship between the alternator pulley and the crank pulley from beneath the car. If the belt appears to turn or bend as it makes its way between these two pulleys, you have found the problem. To adjust alternator pulley alignment, the solution is usually to add spacers between the alternator bracket and case to move the pulley forward, or to sand or lightly grind the bracket or case to move it rearward. Another solution for applications using +4 lb and smaller crank pulley rings is to move the crank idler pulley to the top hole in our idler pulley mounting bracket. This change increases the distance between the crank pulley, crank idler pulley, and alternator pulley, and the increased distance makes the belt less sensitive to minor alignment issues. Please note that this change will require a belt that is at least one inch longer than the existing belt
4. Supercharger Pulley Alignment
Any grooved pulley in the blower drive can ‘steer’ the belt as it moves in the blower drive, and in the case of the Mustang Cobra, the supercharger pulley is the only remaining grooved pulley to consider. We have seen actual instances in which a car’s blower drive was modified (larger crank pulley, more/larger idlers, etc) and then belt alignment became an issue. After much time spent troubleshooting, it was found that the supercharger pulley installed years prior had not been pressed on the shaft fully, and this did not become a problem until larger diameter pulleys were added. While it may seem like an unlikely cause, an improperly-installed (or improperly manufactured, choose wisely) supercharger pulley can create problems. Similarly, some more-recently introduced superchargers seem to create belt alignment problems upon installation. If your blower drive functioned properly before the supercharger upgrade, you have identified the problem.
While not an actual solution to a belt misalignment issue, we have found that using the upper hole in our billet triangular bracket to mount the crank idler pulley will almost always make the belt less sensitive to slight misalignment of pulleys. The upper hole can be used with all crank pulley ring sizes. Please note that when using crank pulley rings sized 8.60” and smaller, this change to the upper hole will impact the calculated belt length required for your application.
All Metco Motorsports crank pulley kits for the Modular Ford applications are designed for use with the OEM balancer*. A balancer that is not an OEM Cobra or Lightning unit may have critical differences that can affect alignment, and any balancer may be vulnerable to excess paint, rust, or scale that can build up on the hub mating surface, preventing the crank pulley hub from seating properly.
To answer another frequently asked question, Metco Motorsports crank pulley rings are machined with no offset. This means that there is no front or rear to the ring, and it can be installed in either direction. In rare instances of alignment trouble, we have heard that simply removing and re-installing the crank pulley hub and/or the crank pulley ring resolves the problem, even when no apparent cause was found during the R & R process.
It is worth noting that the Metco Motorsports crank pulley kits have been in production since the Lightning truck debuted in 1999. The proprietary dimensions used in all of our kits have been proven thousands of times over, and we do not ever deviate from these precise specifications. Our parts are precision-machined to exacting tolerances, and we know our specifications are correct. We do not ever recommend machining or modifying our parts in an effort to resolve an alignment issue. Also, be aware of the knock-offs of these parts that have become available – these parts are simply reverse-engineered copies of ours and can never match the precision of the originals.
In closing, we have never been faced with an alignment issue that we have been unable to resolve. There is a solution to every problem, and it is our hope that the information in this document will assist you in the unlikely event you have a belt alignment problem with your performance car.
Please feel free to contact us any time via phone or email. As a manufacturing facility, our customer service hours are limited and can vary, but if you leave a message, we will always return your call:
P: 864-332-5929
E: [email protected]
*Metco Motorsports crank pulley kits and parts are available in configurations to work with alternate Ford balancers, Innovators West balancers, and ATI balancers. Please call or email for details.