The NuTone 8663RP (for future reference) vent fan in the Black Bathroom began making horrible grinding sounds and, after a day or two, stopped turning. Pulling it out showed the impeller had slipped downward on the motor shaft:
Which meant the impeller was now resting on the steel frame:
Curiously, there’s no retainer under the impeller preventing it from sliding downward, other than good intentions and a friction fit. Nothing lasts, although it’s been working for the last two decades, so I guess it doesn’t owe me much.
My first thought was to build a steel or aluminum collar with a setscrew to hold the thing up, but I decided to try a simple bushing made of UHMW polyethylene between the motor and the impeller.
Turning it to the proper length required a test fit, then another session on a mandrel made from some aluminum tubing:
The snout came out just long enough to clear the motor frame, resting the impeller’s weight atop the bearing around the shaft:
It’s hard to see between the impeller blades, but there’s actually a bit of clearance underneath:
Which left just barely enough room on the top for the retaining clip:
I had high hopes for the UHMW, but it seems any contact between the rotating impeller and the stationary bearing transmits enough sound to be annoying.
So I must break down and build a collar, although it’s off the critical path right now.
As far as I can tell from the pictures, dropping $50 on a new fan unit will get me exactly the same problem. Whether it would last for two decades before failing is an open question, but my experience with freezer fans suggests what we have is as good as it gets and making a bushing is the least-awful way to proceed.