I've noticed on two occasions problems with slipping and noise with non-OEM V belts driving AC comps in cars. Once with replacement belts, from NAPA and once from PEP BOYS. Both times they were name brand, ie. Dayco or Gates belts with typical US sizing nomenclature printed on the belt. The problems have been rapid and repeated slackening after tightening, and noise. Replacing the belts with the OE type metric belts seems to fix the problem, but they are sometimes hard to find. Really a pisser that most auto parts stores seem to only stock fractional belts that really don't work right. Anyone else have this occur? The below is from a Gates bulletin:
Words of caution Before substituting a U.S. belt for its metric equivalent based on an interchange chart, check for dimensional differences in cross sections, length, and belt ride-out (distance a belt extends beyond the sheave OD). For multibelt drives with joined belts, check for compatibility between belt centers and sheave groove spacing A U.S. belt may have a different cross section or length than a comparable metric belt, even though their specification numbers indicate interchangeability. Further, it=92s common to find metric belts in nonstandard cross sections and lengths that can=92t be easily interchanged with U.S. belts. Some interchange catalogs list differences in length between equivalent U.S. and metric belts, with these differences typically ranging up to 1 in. for the longest belts. The difference in length that can be tolerated depends on the application and the amount of take-up. It is usually up to the equipment operator or maintenance engineer to decide if the difference in length is acceptable for a particular application. Differences in belt ride-out and included angle of the cross section between equivalent U.S. and metric belts can adversely affect the speed ratio of the drive, as well as power capacity. Because of differences in groove spacing between U.S. and metric sheave, Figure 2, interchanging joined US belts with joined metric belts causes the belts to seat improperly in the sheaves. This leads to early belt failure and rapid sheave wear. If you=92re unsure about the effect of any dimensional differences on your application, consult the belt manufacturer. Failure to use compatible replacement belts can lead to reduced belt service life and lost production due to