Friday, August 26, 2016

A Grubby Old Electric Space Heater With A Noisy Fan Motor

This old heater has outlasted its warranty period by decades.

I haven't cleaned it in a long time, so it needs to be at least partially dismantled for a good cleaning. It's also exhibiting a clattery fan motor bearing, so I need to look into that and see if I can come up with a solution.

A single, vertical tie-rod and two thermostat connections are all that need to be undone for lid and cover removal.

Three screws and two spade terminals are what's holding the heating element in place.

The fan has its own mounting brackets held in place by four screws, plus its two spade terminal connections that piggy-back onto the heating element's connections.

And here's the fan out of the heater's base, with its mounting brackets still in place.

Note the dust accumulation on the leading edges of the fan blades. The dust accumulation throughout the heater is awesome. Any fan-cooled household appliance is susceptible to such accumulation, and ought to be periodically inspected for it and cleaned of it. I've let this heater go for too long without tending to it.

The fan motor exhibits just the condition I expected it to; i.e. perceptible, excessive clearance in its fan-end sleeve bearing. That accounts for the noise that it makes.

Next up is to pull off the fan. Then I'll be able to dismantle the motor, and see if there's anything I can do about the bad bearing. Here's a view of the fan being pulled off by a little puller I devised for this.

With the fan off, I dismantled the motor and got a good, close look at its fan-end bearing. It turns out that the bearing/shaft interface is just fine -- that was not the source of the excessive clearance and noise I'd observed. Instead, the spherical, self-aligning sleeve bearing is loose in its keeper inside the mount. Here's a view of the bearing in its keeper in its mount.

I could see no way to snug up the spherical bearing in its keeper, but the fact that both bearing mounts in the motor are identical gave me an idea. I transposed the two bearing mounts, so the good one was at the fan end of the motor. I reinstalled the fan and gave the assembly a trial run. That appears to have done the trick.

I'll clean and reassemble the heater, and see if my repair method has truly cured the fan motor of its noisy operation.

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Transposing the two bearing mounts worked. The motor now runs quietly.

The reason it worked lies in the distribution of radial forces between the motor's two bearings. Any slight imbalance of the fan's blades results in a radial force that must be borne by the motor's bearings. By far, most of that force is borne by the bearing nearest the fan. Since that was the loosely retained bearing, it would tend to clatter within its keeper.

Moving that loose bearing to the other end of the motor relieved it of absorbing the radial forces exerted by the fan -- clatter gone.

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