First check for wear and tear on the pulleys. The pulley should be free from oil, dirt and grease. The pulley should also be aligned correctly. Ensure that the V belt is in good condition and of the correct type for the application. Slip the belts onto the drive without stretching or forcing them on. The drive units should be brought together so that the belt can be slipped on. Adjust the centre distance between the pulleys to achieve the right tension in the belt. Allow about half an inch of slack in the belt.