How to stop motor shaft nut from coming off?

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azad   10 mW

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How to stop motor shaft nut from coming off?

Post by azad » Oct 30 2019 8:55am

Hi,

The motor shaft nut comes off of sprocket and shaft rotates inside the sprocket without the sprocket being rotated. How can I stop the nut from falling off?
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\ (•◡•) /   1 W

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Re: How to stop motor shaft nut from coming off?

Post by \ (•◡•) / » Oct 30 2019 9:10am

azad wrote:
Oct 30 2019 8:55am
Hi,

The motor shaft nut comes off of sprocket and shaft rotates inside the sprocket without the sprocket being rotated. How can I stop the nut from falling off?
you need nordlocks. They really do work great.

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scootergrisen   10 W

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Re: How to stop motor shaft nut from coming off?

Post by scootergrisen » Oct 30 2019 9:30am

Maybe a woodruff key would help.
And maybe a nut with like 3 times more area to touch the aluminium.

Punx0r   100 GW

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Re: How to stop motor shaft nut from coming off?

Post by Punx0r » Oct 30 2019 10:10am

Is there a key in that keyway? Is the shaft and sprocket tapered?

As a first-try solution I'd thorough degrease all parts and use loctite on the threads. Blue is normal strength, red is much stronger but beware you'll need to apply heat if you ever wanted to get it apart again.

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E-HP   100 kW

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Re: How to stop motor shaft nut from coming off?

Post by E-HP » Oct 30 2019 11:26am

azad wrote:
Oct 30 2019 8:55am
Hi,

The motor shaft nut comes off of sprocket and shaft rotates inside the sprocket without the sprocket being rotated. How can I stop the nut from falling off?
Is the sprocket deeper than the one that came with the motor? It looks like the nut would usually tighten up against the shoulder of the shaft where the threads end, so having it only contacting the sprocket may make the nut do the work that the key would normally do.

aroundqube   1 kW

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Re: How to stop motor shaft nut from coming off?

Post by aroundqube » Oct 30 2019 1:28pm

I would try a key long enough to go to the end of the keyway, and use 2 heavy vibration locknuts. Place a thin one on second, to act as a jam nut. These parts are available here : https://www.mcmaster.com/hex-locknuts

Balmorhea   1 kW

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Re: How to stop motor shaft nut from coming off?

Post by Balmorhea » Oct 30 2019 2:14pm

The shaft is right hand threaded. If it's on the right side of the bike, motor torque will be applied in in a way that tends to unscrew the nut.

Usually, this tendency would be mitigated by the key keeping the sprocket from rotating on the axle. But it looks like you don't have a key on the motor shaft. That's the part you need to fix. The retaining nut is not for keeping the sprocket from spinning on its shaft. It's just for keeping everything stacked up together.

azad   10 mW

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Re: How to stop motor shaft nut from coming off?

Post by azad » Oct 30 2019 8:38pm

Punx0r wrote:
Oct 30 2019 10:10am
Is there a key in that keyway? Is the shaft and sprocket tapered?

As a first-try solution I'd thorough degrease all parts and use loctite on the threads. Blue is normal strength, red is much stronger but beware you'll need to apply heat if you ever wanted to get it apart again.
I think there isn't a key on the shaft. Yes I think shaft is tapered. It starts at 10mm and gradually increases the diameter. 11mm is the diameter of the sprocket.

azad   10 mW

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Re: How to stop motor shaft nut from coming off?

Post by azad » Oct 30 2019 8:39pm

E-HP wrote:
Oct 30 2019 11:26am
azad wrote:
Oct 30 2019 8:55am
Hi,

The motor shaft nut comes off of sprocket and shaft rotates inside the sprocket without the sprocket being rotated. How can I stop the nut from falling off?
Is the sprocket deeper than the one that came with the motor? It looks like the nut would usually tighten up against the shoulder of the shaft where the threads end, so having it only contacting the sprocket may make the nut do the work that the key would normally do.
No the sprocket is the same as before. I am just replacing the old one. The freewheel of the earlier one got jammed and the same thing had started to happen with it.

azad   10 mW

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Re: How to stop motor shaft nut from coming off?

Post by azad » Oct 30 2019 8:43pm

Balmorhea wrote:
Oct 30 2019 2:14pm
The shaft is right hand threaded. If it's on the right side of the bike, motor torque will be applied in in a way that tends to unscrew the nut.

Usually, this tendency would be mitigated by the key keeping the sprocket from rotating on the axle. But it looks like you don't have a key on the motor shaft. That's the part you need to fix. The retaining nut is not for keeping the sprocket from spinning on its shaft. It's just for keeping everything stacked up together.
How should I fix the key part? I have an 11mm sprocket and shaft has varying diameter starting at ~10.5 with max 12mm at the end.

azad   10 mW

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Re: How to stop motor shaft nut from coming off?

Post by azad » Oct 30 2019 9:02pm

This is how motor shaft looks.
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Balmorhea   1 kW

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Re: How to stop motor shaft nut from coming off?

Post by Balmorhea » Oct 30 2019 9:09pm

azad wrote:
Oct 30 2019 9:02pm
This is how motor shaft looks.
That shaft has been eaten up because there wasn't a key to keep it from spinning in the sprocket. The sprocket bore may be damaged, too.

If it were my motor, I'd get a new one, (and a key for the shaft keyway). The sprocket needs to fit tightly on the shaft.

John in CR   100 GW

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Re: How to stop motor shaft nut from coming off?

Post by John in CR » Oct 30 2019 9:12pm

It looks used enough to graduate to a more efficient more quiet brushless motor setup.

aroundqube   1 kW

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Re: How to stop motor shaft nut from coming off?

Post by aroundqube » Oct 30 2019 9:16pm

could be a half moon or Woodruff key : https://www.mcmaster.com/machine-keys

Balmorhea   1 kW

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Re: How to stop motor shaft nut from coming off?

Post by Balmorhea » Oct 30 2019 9:18pm

aroundqube wrote:
Oct 30 2019 9:16pm
could be a half moon or Woodruff key : https://www.mcmaster.com/machine-keys
It's a regular square key with radiused ends. Only it isn't there.

A Woodruff key seat is shaped like the rounded side of the key.

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E-HP   100 kW

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Re: How to stop motor shaft nut from coming off?

Post by E-HP » Oct 30 2019 11:38pm

azad wrote:
Oct 30 2019 8:38pm
I think there isn't a key on the shaft. Yes I think shaft is tapered. It starts at 10mm and gradually increases the diameter. 11mm is the diameter of the sprocket.
I assume you mean the sprocket hole is 11mm on the inner side and 10mm on the nut side?

Otherwise, the seller sold you the wrong sprocket.

Edit: I don't see the gradual increase in diameter in the picture of the motor shaft. I see the step.

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dogman dan   100 GW

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Re: How to stop motor shaft nut from coming off?

Post by dogman dan » Nov 01 2019 7:28am

Nut should stay on better, with the key in there. Locktight it too.

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scootergrisen   10 W

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Re: How to stop motor shaft nut from coming off?

Post by scootergrisen » Nov 01 2019 2:38pm

There is a problem with the chain on picture 3.jpg in case you did not know.

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E-HP   100 kW

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Re: How to stop motor shaft nut from coming off?

Post by E-HP » Nov 01 2019 4:30pm

scootergrisen wrote:
Nov 01 2019 2:38pm
There is a problem with the chain on picture 3.jpg in case you did not know.
Good eye!

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