Large deep cracks on the belt interior with no signs of general surface roughness on the belt interior, are usually the result of insufficient belt tension. When adjusting belt tension, always start by relaxing all tension on the rubber belt. Always place new marks 12 inches (305 mm) apart on the edge of the relaxed belt. For belts thicker than 2 inches (51 mm) stretch the belt until the marks are 12-1/4 inches (311 mm) apart. For belts less than 2 inches (51 mm) thick, stretch the belt until the marks are 12-1/2 (318 mm) apart. After stretching the belt always rotate the belt several revolutions and again measure the distance between marks again. Re-adjust the tension to the correct amount and again rotate the belt several revolutions and again measure the marks. Continue to repeat these operations until the marks remain at the desired distance apart.