Furnace Fan Noisy

[Coco]

I have a 20 year old forced air natural gas furnace. In the last few days, the furnace fan wouldn't come on or wouldn't stay running very long. It was getting power, but not turning and getting very hot. I replaced the old 1/4 hp motor with one of similar specifications (still 1/4 hp - although the new motor is a 48 frame replacing the old 55 frame motor). The new motor was better, but still had trouble getting started. So I took the squirrel cage type fan out and cleaned up the shaft and bearings and reinstalled. I'm hoping you can help me with some questions.

Questions: Should you replace the fan (squirrel cage) shaft bearings? They look like a brass sleeve surrounded by a closed shell that I think is filled with grease.

Also: When my fan motor is running you can hear a humming throughout the house. What can I do to make it quieter? Could it be an isolation problem?

For background, the motor is attached solidly to the fan housing, and drives the fan via a belt and two pulleys. The fan pushes air upward through a square shaped opening into the furnace. The rear edge of the opening fits up in the furnace opening, and you tilt the front edge up and two bolts hold it up.

Thanks very much for your help.

[HayZee518]

The two bolts you say that hold the motor up provide tension for the belt. to lessen the noise you could put a couple of rubber pads under the bolt heads and then tighten them up for tension. The bearings you speak of for the squirrel cage are oil-lite bearings. They sit in a spring like cage with felt in it. This type of bearing uses oil for lubrication. Use a light machine oil and saturate the felts. The oil will make its way into the bearing. The oil-lite is called sintered bronze and is porous.

[Coco]

Thanks HayZee. I'll give it a try. Do the bearing cages come apart so I can saturate the felt? or do I drip the oil between the two cage halves?

Thanks.

[HayZee518]

just drip the oil on the felts. once they start taking oil {i.e. dry felt} it'll soak it up quickly. put some oil on the bearing surface and re-assemble the fan shaft. THIS oiling will help speed up the capillary action through the sintered bronze.