Auger Motor Armature Endplay

[Dirtbiker]

I have an older Whitfield Advantage pellet insert. I had an overfeeding issue one night and the auger mysteriously had stopped operating. I removed the motor and auger, carefully inspecting for foreign objects, bushing wear and so forth...nothing. Tested the motor and gearbox, which seemed to be operating properly, now all back together and working fine. Cause is a mystery.

One thing that I noticed is the end of the motor armature shaft is formed into a helical pinion gear to engage the gearbox. Didn't think about it at the time, but that armature appeared to have a whole lot of endplay in it...maybe 3/16". It occurred to me that maybe the helix isn't engaging fully any more because of this. Any thoughts on what the proper end play should be and what material I should use to make it proper?

 

[SidecarFlip]

Most armature shafts will have fiber washers on them (between the armature shaft and the rotor) to mitigate end play. At the age of yours, I'd suspect the washers petered out and fell off. A trip to the hardware store will get you some appropriate sized fiber washers you can add to the armature shaft. Put them on the opposite side of the helical input (outboard motor bearing) and while it's apart, oil the outboard beating with light machine oil when you have it off (outboard bearing retainer).

The inboard side is lubricated by the grease in the gearcase, which, in your case is probably hard as a rock and not doing much anyway. If I were you, I'd grease the gearcase by drilling a small hole 1/8" or 1/16" at the top of the case and use a needle greaser or a chainsaw roller nose greaser and grease the gearcase until you see grease oozing out from around the bronze bushing where the armature shaft enters the gearcase. That will lube the bearing and insure the gearcase has sufficient grease.

I've never had a motor or gearcase failure in over 20+ years but I keep everything oiled and greased and I do it during spring shutdown.

3/16" is a bit excessive, should be about 1/8"

 

[Dirtbiker]

Thank you SidecarFlip. That's exactly the information that I was hoping for. Fiber spacers may be hard to come by. I'm considering using Nylon washers as this is not in a high heat area of the stove.

 

[SidecarFlip]

Those will work too. Just use non-metallic washers. Your local ACE should have the fiber ones, mine does.

 

[Dirtbiker]

Perfect SidecarFlip. I'll post the dimensions next time I pull the stove out and take the motor apart.

 

[SidecarFlip]

Do keep in mid that you want the armature roughly centered in the field laminations. If it's way off to one side the power of the motor is diminished, not that they have a lot to begin with....

 

[Dirtbiker]

Great point SidecarFlip. I removed the auger from the stove and attached it directly to the motor assembly...allowing it to cycle and apply the torque against the force of my grip. Makes plenty of power and no other issues found. I was astonished at how the lam stack would get pulled toward anything metal when it cycled on!

 

[SidecarFlip]

Simplest motor ever made (and cheapest too).

 

[Dirtbiker]

OK All...I have a follow-up to this conversation. I took the motor and gearbox apart to clean/regrease. No issues found and the grease was still semi pliable. I went to my local Ace for fiber washers...nothing! Then I discovered the perfect source, the little underhead fiber washers used in drywall anchors that act as a bearing between the screw head and anchor body. Perfect size and thickness! Tried (2) washers and it bound the motor armature. One ended up just perfect and the end play is successfully reduced.

 

[SidecarFlip]

You have to be careful about how many washers used. The motors themselves have little torque (which is inherent in a fractional horsepower shaded pole motor) and why the gearboxes are quad reduction. The gearbox increases the delivered torque and reduces the armature rpm to a useable value.

Any binding of the armature of the motor will cause it to stall. There has to be some freeplay for it to rotate which is why it's important to keep the cheap bearings lubricated too.

One thing I do when I have them apart is, I take 000 steel wool and dress both the armature and the inside of the field laminations to makes sure there is no crud. Any crud on the armature or inside the field laminations will also stall the armature. Cheap motors and cheap reduction gearboxes and most gearboxes have minimal lubrication (grease) from the factory because, they want them to fail so you purchase a new one.

 

[Dirtbiker]

Absolutely right SidecarFlip. I initially tried using (2) fiber washers [they are .025" thick each] and it did indeed bind the armature. Removed one of them and the clearance was just perfect. Ran the motor for 10 minutes and no binding.

 

[SidecarFlip]

You really want the gearbox full of grease which is why I suggest drilling a small hole (1/8" or 1/16") at the top front of it (where you can access it easily) and filling it with grease until it oozes out from around the bushing where the armature shaft goes in. That entrance has a bronze bush and it's not grease tight so it will come out there when the reduction gearbox is almost full of grease. Like I said, I use a needle greaser on my grease gun or a chainsaw roller nose grease gun. Either works.

In the past, I've drilled and tapped them for zerk fittings but it's quicker and easier to just drill a hole and use a needle greaser.

From the factory (China or where ever, they put a very minimal amount of grease inside and the grease gets hard and the gearbox eventually fails and you buy a new one and rinse and repeat. No reason to have them not last a long time. Mine are all going on 20 years plus with no replacements.

 

[Dirtbiker]

For sure a great idea SidecarFlip. While I didn't completely pack the case, I filled the cavity with Lubriplate GR-132 Portable Tool Grease. It's a lithium based grease with an operating temperature of +430 F to -40 F, and according to the MSDS is "ideal for use in fractional horsepower gear cases". It oughta outlast me!