Electic Motor Ignorance

He folks,
I have a buck stove insert with a really really noisy fan. I've pulled the stove out to try and remedy the situation. What I found is that the shaft of the motor has a certain amount of play in the housing. not left right, but front/back. IE, If you hold the housing, you can push the end of the shaft forward or pull it back about 1/4 inch.
The shaft extends an inch or 2 out the front, and maybe 1 inch out the back of the housing, and there is a fan on the front, and what I guess is some type of balancing fan ( much smaller) attached to the back. The play front and back of the shaft in the housing is causing all the noise.
My question is, is that normal? should the "drive shaft" on an electic motor have some play in any direction? Is the the play in the shaft there by design?
The replacement motor I found is here http://www.cshincorporated.com/product_info.php/products_id/257
Dave
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That play is about normal
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Many very small motors have some play in the shaft. Of course, not knowing the factory specs no one can say if your is worn beyond acceptable limits. Many of those small motors also have sleeve bears and they wear faster than ball bearings. You may get by for a while with a shot of lubricant, but long term, the motor is probably on the way out.
You may be able to find a cheaper replacement from www.grainger.com
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How large a motor is this?
If the motor has ball bearings, there will be very little end play, probably too little for you to feel. But it's pretty common for fractional-horsepower electric motors to use bronze sleeve bearings instead of ball bearings, and sleeve bearings allow for axial movement of the shaft through the bearings. There will be thrust washers of some sort to prevent the shaft from moving *too* far, but there may be substantial end play between the two points where the thrust washers operate.
But why is it noisy? Even with sleeve bearings, the motor is usually put together so that the magnetic field (when operating) pulls the rotor to a point about half-way between its limits of play, and the thrust washers don't need to do anything. If this motor drives a fan, and the fan blows air parallel to the shaft, then it will put some end thrust on the shaft and might even pull the shaft against one end of its travel. Mounting the motor with the shaft vertical may do that too, courtesy of gravity. Even then, the thrust bearing is steel running on bronze, and should be quiet unless worn or unlubricated.
    Dave
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On Dec 7, 2:48 am, snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote:

Its not a very large motor at all, it only powers a fan for the stove, nothing else. its has 3 speeds controlled by a heat sensitive switch. the fan makes the most noise at lower speed.
what I think is making the noise is the shaft is banging back an forth in the housing. the air pressure from the fan blade pushes the shaft back in the housing, but I'm guessing the magnetic force tries to pull it to the center like you mentioned. so when its on slower speed, the shaft has less air pressure, and can "bounce" when its on a higher speed, the fan pressure overpowers the magnetic force and pushes the shaft back in the housing.
the noise it makes is not a squeaky bad bearing noise, but a "bang,bang" sound of the shaft hitting front and back, this is amplified by the cast stove, and makes such a racket that you can't talk over the sound.
I guess I'm nerveous about buying a new motor if is just going to start acting in the same way as the existing one, which from an operational standpoint still works perfectly.
Dave
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Has it always been noisy? Have you run it when not mounted in the stove and is is noisy then?
I it possible that something has caused the fan to be out of balance.
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Zephyr wrote:

I'd take it apart enough to make sure it's the axial movement that's the problem (hitting on either end, not the sides) and if so, just add an appropriate thickness of nylon washer(s) to take up enough of the end play to stop it.
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dpb wrote: ...

Of course, be sure to only add sufficient to stop whatever is hitting, don't add enough to make the shaft hard to turn...
Oh, one other thought -- it's possible particularly if it is a squirrel cage fan the fan itself has moved on the shaft or simply needs to be adjusted a little in one direction or the other.
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