Friday, September 5, 2014

Noma Gran Prix Snow Blower -- Impeller Bearing Failure

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NOTE; I was remiss here in not photographing and documenting this matter as I took the machine apart. I'll try to do a decent job of recording the reassembly. I hope the reader may still find it of some interest or use.

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The old snow blower my son bought turned out to have a severely worn impeller[1] bearing.[2] Here's a view of the thing removed from the rear of the snow blower's scoop where it resides.

It's well and truly 'game over' for that bearing.

The previous owner of the snow blower had continued to use the machine with the ruined bearing in place. That had the effect of hammering down the diameter of the impeller's shaft under the inner race of the bearing. The shaft there was about 0.013" undersize from its original 7/8" diameter.

The only way to get the shaft fit for service again was to have a machinist knurl the undersize portion, to raise crests that would again fit the inner race of a bearing. Here's a view of the knurling job done.

The crests of the knurls now represent a slight oversize of 7/8" diameter. To be able to reassemble the mechanism, I'll have to file the crests down just enough to give me a sliding fit in a new bearing. I'll do that by hand on my wood lathe, using the old bearing as a reference. Here's a view of that setup.

Done. The new bearing is now a sliding fit on the knurl.

At final assembly, I'll apply some Loctite retaining compound to the knurl, so there'll be no looseness to the bearing's fit on the shaft.[3] That may be a bit of an iffy proposition, because I'll be asking quite a lot of the retaining compound -- the retaining compound may not cure in voids as large as the knurls' valleys. Should that transpire, I'll redo the assembly with CA adhesive instead of retaining compound.

Anyway, it's time to get the impeller reassembled with its gearcase and the augers.

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And here's the whole auger/gearcase/impeller affair back together and ready for installation.

Tomorrow, weather permitting, I'll get all that back into the scoop along with its new bearing.

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The Weather Cooperated -- SATURDAY, SEPTEMBER 6, 2014

And here's the new bearing bolted in place at the rear of the scoop.

Here's the auger/gearcase/impeller assembly stuffed back into the front of the scoop.

And here's the impeller's shaft-end in place at the rear of the scoop, awaiting its pulley.

The machine is ready for final reassembly.

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All Done -- MONDAY, SEPTEMBER 8, 2014

Here's the machine back together.

And here's a closer view of the v-belt transmission.

The locomotion belt at the right has no tension adjustment. Its tension is set by its spring-loaded idler pulley.

The auger drive belt at the left is adjustable for tension -- its idler can be repositioned in a slot for optimal tension when auger drive is engaged.

From what I've seen on this machine, snow blower auger/impeller drive is a brutal, stressful job. It's an area in any used machine that's likely to need attention. All in all, I think my approach to repairing this one was sound. The proof will be in how it stands up to the coming winter's work.

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[1] "Impeller" is my term for the second stage element of a two-stage snow blower. The 'auger' is the first stage. The auger sweeps up snow and hands it off to the second stage, the 'impeller'. The rotating impeller hurls the snow up and out the chute.

[2] The bearing's description as it appears on the sales receipt from my parts dealer is, "44-053: 9648/780048 Canadiana Keyed Bearing". It's a 1640ZZ bearing with a 3/16" keyway in it's inner race. Dimensions are 7/8" bore x 2" O.D. x 9/16" thick.

[3] As it turned out, I decided against using any retaining compound or adhesive at the bearing's inner race, where it fits over the shaft.

The bearing is an easy sliding fit on its shaft, even where the shaft still has its undamaged, un-knurled surface. The fit has to be relatively loose for the sake of ease of assembly. Were it a snug fit, it would be extremely difficult to install the auger/gearcase/impeller assembly in the scoop. That's no doubt why the bearing's inner race is keyed -- so that the loose fit won't result in the shaft turning within the bearing; the keying forces the bearing to be operative, in spite of the loose fit of the shaft.

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  1. Thanks Tom! Very helpful, back blowing snow now, appreciate the post.


  2. Thanks Tom, Nice trouble shooting Post