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I took apart my in-wall furnace and found that the fan blades are loose with the fan hub so when the motor starts or stops, the blades don't receive any torque and they make a lot of noise.

The pieces of the fan look kind of like this: http://airdrive.com/products/hubs/

I'm just trying to understand how I can mechanically or chemically attach the two pieces as I'm assuming they should be attached. I tried soldering and that obviously didn't work (didn't really expect it to either). Maybe there is some loctite glue I can use that will chemically bond them?

Here are some photos: http://imgur.com/a/pc5X9

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  • Can you show some photos of the actual hardware? You can put arrows on the photo to show us where there appear to be gaps/insufficent friction. – Andrew Morton Feb 25 '17 at 19:01
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These blades typically have a boss that has a set-screw and also might be "keyed" (i.e. has a round hole with a flat spot, to mate with a shaft equipped with a flat area, to provide a landing surface for the set-screw).

Your problem sometimes occurs when the set-screw has come loose due to vibration; check it and tighten if necessary. It is also possible that the boss in the fan blade/propeller was damaged by the spinning shaft, because the set-screw was loose; this normally requires fan blade replacement.

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  • I'm having trouble understanding what this boss thing is. I don't see anything that would indicate the hub is keyed to the fan blades at all – Joe Phillips Feb 26 '17 at 21:57
  • It is also (perhaps more appropriately) called the hub; the same device on an airplane propellor is called a boss. In your picture it appears that the blade's hub has a set-screw holding it to the motor shaft; the set-screw position should align with a flat spot on the shaft to help prevent it from "free-spinning". – Jimmy Fix-it Feb 27 '17 at 1:03
  • Yes, the set screw keeps it from spinning on the shaft. That works fine. The blades themselves are what spin out of sync with the hub. – Joe Phillips Feb 27 '17 at 2:18
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Order a new fan blade assembly, it will save you in the long run. They are generally welded together in the factory or press fit together (blades are keyed so as the button insert will not rotate). The fan blade can be purchased from either an online appliance repair shop or a local dealer. I think it will set you back about $25-$30. Faster, cheaper (in the long run) and first time it works.

EDIT 2/28/2017

There are two options , one is kind of hacky and requires some mechanical aptitude but is a cheap possible fix. Using a couple large washers - you could use screws to attach the washer onto the spindle mount (probably a 7/16 or 3mm thread size) on one side and set the other washer on the other side (I would probably use JB weld between the washer and the blades. and then secure the washers to the shaft with another set of 3 screws (even spaced around) and use nylon self locking nuts to retain it. [Cheap and should do the job.] However I will warn you depending on the speed of the blades - the force of starting could degrade the blades where your retaining screws lock one side to the other and it could end up not working at all. Big enough washer and locked down tight enough - you might get away with this. - remember the fan spins so if your retaining screws are not in the same arc and of the same weight - the blades will not be in balance. (the closer to the shaft the screws - the less Centrifugal force = better.)

The only other option I have for you is to get a replacement motor and fan assembly to fit it.A Motor and fan assembly is probably $100. but beats a new furnace. A Local Appliance repair should be able to provide you a cross reference fan assembly to fit. Who knows maybe they can tell you a good blade assembly that perhaps needs a simple reducer bushing to mount it.

I am assuming you removed the locking bolt on the fan blade , and when you say the blades turn loosely - you mean the spindle mounting of the blades turns freely in the fan blade assembly. You are correct - that should not spin freely - it should be secured to the blades. and the locking bolt secures it to the motor shaft.

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  • This particular fan isn't sold anymore. How would I find a suitable replacement? – Joe Phillips Feb 26 '17 at 18:13
  • I checked with Dey Distributing and they couldn't find a replacement – Joe Phillips Feb 28 '17 at 0:14
  • @JoePhillips Since there is no replacement available - the fan is most likely aluminum - welding is really not a good option - it will probably distort the fan blades. I added to my answer as comments are not long enough. – Ken Feb 28 '17 at 6:37
  • The washer idea is probably the way I should have gone but... I did something else because it seemed like it would work and would be easier. And it's working so far – Joe Phillips Mar 1 '17 at 3:57
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I once had a similar type of fan blade to hub connection failure. A replacement fan blade assembly was not immediately available so I removed it for repair. The parts were cleaned and then epoxy was used to glue it back together. The brand JB-Weld was used and the fix lasted until a new motor & fan unit was delivered.

Note that with epoxy usage on a fix like this it is not sufficient to just put the stuff between the mating surfaces of the metal. Instead is necessary to build up a good fillet of the epoxy around the hub assembly.

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This is going to sound hacky as hell, as it is, but it seems to be working so far after a few heating cycles.

The hub on the fan has a tiny lip that extends over the back side of the fan. This is less than 1/16" I'm guessing so I didn't have much to work with. I used an awl (basically an ice pick) to hammer in a few "indentations" from the lip into the fan itself. This gave the hub some teeth to hold on to the fan with. It actually feels quite secure but I have no doubt it will eventually fail over time. This at least should buy me enough time to get a replacement unit since I'm basically out of ideas at this point.

I also bent the fan blade fins to they were less torquey. I did this because I didn't want the force of the fan spinning to dislodge my hacky fix and also because it's an old unit, everything rattles, and it just seemed quieter and safer.

Edit: This lasted only a few days but I didn't put any JB Weld on it or anything which probably would have helped a lot. The awling I did to the fan seems to still be holding it in place but the fan is just so misaligned at this point that I didn't want to put any effort into saving it so I just unplugged it and I'm running the furnace without a fan for now. I picked up a whole new unit tonight that should work a lot better.

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  • Joe, this seems like a great fix for when the hub is spinning around on the blade attachment point. They should have done a better job peening that hub to the blade. You might want to add the suggested step of JB Weld or some other solid epoxy filler. You should accept your own answer. – Jimmy Fix-it Mar 10 '17 at 2:57

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