Index Home About Blog
From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Furnace making a loud noise
Date: Thu, 09 Nov 2000 17:34:25 -0500

George Thompson wrote:

> Turned on my furnace for the first time this season and it immediateley made
> a loud noise.  sounds like either the motor has a bearing shot or the blower
> wheel is rubbing on something.  The furnace works fine other than the noise.
> I plan on taking it to then shop, but can't do that for anothr month.  I
> have a short trip planned next week and will need to use the furnace. Has
> anyone had this happen to them and does anyone think I will cause any
> serious damage by using the furnace.
> Thanks

What has likely happened is the oil felt in the bearings has dried
out from age.  Over the summer the shaft formed a film of rust.
When you started the blower, this film of rust caused the shaft to
squeal.  If you continue to run the fan when it is squealing, the
bearings will be quickly worn out by the vibration and the rust dust
which is abrasive.  Short of replacing the fan motor ($$$), the only
solution is to remove the fan motor and lube the bearings.
Dribbling oil down the shaft will put lube on the bearing but it
will not rewet the oil felt.  The only way to do that is to gain
access to the felt.  Since very few if any of these motors have oil
holes, the solution is to drill a small hole in the felt housing.
The bearing itself is almost always oval and the housing is stamped
to follow that contour.  Below that egg-shaped bulge around the
shaft will be a larger thick washer-shaped area.  This is the oil
felt.  A small hole is carefully drilled through the housing, oil
introduced (a medical syringe and needle is easiest) and then the
hole is sealed with a dab of  silicone RTV.  Both ends must be
done.  If the motor is old, it may take awhile for the new oil to
soak into the old felt.  Be patient.  A little WD40 will soften the
old oil.  Follow this with some light machine oil.

Ideally one should disassemble the motor and clean out any brush
dust but many of these motors are spot welded or crimped shut and
are difficult to open.  If you have the time and inclination,
disassembling the motor to clean it out and inspect the brushes and
commutator will repay you handsomely with extended life.  If you do
disassemble the motor, you can access the oil felt from the inside
and so won't need to drill the housing.

My heater did exactly what you describe when I turned it on
earlier.  Now that I've overhauled the motor, it's much quieter, the
amp draw dropped from 8 to about 6 and the added air flow means the
overtemp cutout is no longer tripping.  A very worthwhile thing to
take care of.


Index Home About Blog