I have a 30+ year old hot air furnace that has developed a noise coming from the wheel on the air blower. There is play in the wheel, but I don't know how much play is normal. The motor that runs the belt to the wheel is quiet and has had no adjustments since installed 10 years ago. The belt is dry on the outside but not brittle or dry on the side that rotates the wheel. The set screw that holds the wheel in place is tight. My question is how much play is normal, could it be the belt that is causing the noise from the wheel? Could it be dirt? I am positive the noise is from the wheel so any suggestions on trouble shooting it would be appreciated.

Try a small bit of lube on the bearings if you can get to them. There is no published spec on shaft play that I know of listed by the HVAC manufactures.