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NuTone 8663RP Bathroom Vent Fan: Effective Repair

My high hopes for the UHMW bushing supporting the impeller lasted the better part of a day, because direct contact between the impeller and the motor bearing produced an absurdly loud and slowly pulsating rumble:

Bath Vent Fan - bushing installed
Bath Vent Fan – bushing installed

My hope that the UHMW would wear into a quieter configuration lasted a week …

Back in the Basement Shop, some free-air tinkering showed the impeller produced enough suction to pull itself downward along the shaft and jam itself firmly against the motor frame. My initial thought of putting a lock ring around the shaft to support the impeller turned out to be absolutely right.

So, make a small ring:

Bath Vent Fan - small lock ring - c-drill
Bath Vent Fan – small lock ring – c-drill

With a 4-40 setscrew in its side, perched atop the impeller for scale:

Bath Vent Fan - small lock ring - size
Bath Vent Fan – small lock ring – size

It just barely fits between the impeller and the motor frame:

Bath Vent Fan - small lock ring - installed
Bath Vent Fan – small lock ring – installed

This reduced the noise, but the hole in the impeller has worn enough to let it rotate on the shaft and the rumble continued unabated. The correct way to fix this evidently requires a mount clamped to both the shaft and the impeller.

Fast-forward a day …

A careful look at the impeller shows seven radial ribs, probably to reduce the likelihood of harmonic vibrations. After a bit of dithering, I decided not to worry about an off-balance layout, so the screws sit on a 9 mm radius at ±102.9° = 2 × 360°/7 from a screw directly across from the setscrew in another slice from the 1 inch aluminum rod:

Bath Vent Fan - mount ring - tapping
Bath Vent Fan – mount ring – tapping

Centered on the disk and using LinuxCNC’s polar notation, the hole positions are:

G0 @9.0 ^-90
G0 @9.0 ^[-90+102.9]
G0 @9.0 ^[-90-102.9]

As usual, I jogged the drill downward while slobbering cutting fluid. I loves me some good manual CNC action.

Put the mount on a 1/4 inch tube, stick it into the impeller, and transfer-punch the screw holes:

Bath Vent Fan - mount ring - impeller marking
Bath Vent Fan – mount ring – impeller marking

Apparently, some years ago I’d cut three screws to just about exactly the correct length:

Bath Vent Fan - mount ring - test fit - bottom
Bath Vent Fan – mount ring – test fit – bottom

I knew I kept them around for some good reason!

The 9 mm radius just barely fits the screw heads between the ribs:

Bath Vent Fan - mount ring - test fit - top
Bath Vent Fan – mount ring – test fit – top

Some Dremel cutoff wheel action extended the motor shaft flat to let the setscrew rest on the bottom end:

Bath Vent Fan - mount ring - shaft flat
Bath Vent Fan – mount ring – shaft flat

Then it all fit together:

Bath Vent Fan - mount ring - installed
Bath Vent Fan – mount ring – installed

The fan now emits a constant whoosh, rather than a pulsating rumble, minus all the annoying overtones. It could be quieter, but it never was, so we can declare victory and move on.

Dropping fifty bucks on a replacement fan + impeller unit would might also solve the problem, but it just seems wrong to throw all that hardware in the trash.

And, despite making two passes at the problem before coming up with a workable solution, I think that’s the only way (for me, anyhow) to get from “not working” to “good as it ever was”, given that I didn’t quite understand the whole problem or believe the solution at the start.

But it should be painfully obvious why I don’t do Repair Cafe gigs …

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