Help! Ebike back hub motor help

Billyrobbo

Finding my (electric) wheels
Jul 17, 2019
7
0
I’ve recently bought a second hand converted ebike and after about 2 days riding my back wheels suddenly became lose and after putting back on , every time I activate the throttle the back wheel spins off the bike , I believe the axle is spinning with the wheel please help , thanks
 

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Benjahmin

Esteemed Pedelecer
Nov 10, 2014
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It looks like the motor axle is not deep enough into the dropouts, they need filing so it sits fully in. Also, in my opinion, to fit any hub motor without a torque bracket is asking for trouble. You need something like this:
I,ve used these, they are robust, however they do need something like a mudguard or rack boss to fit to. Otherwise you can use something like this:

Make sure it is the right size for the axle on your motor. As the axle is already spinning I'd say use one either side.
Don't use the bike until you've done this, you could be in for a nasty accident.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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You should never fit a motor like that in an aluminium frame without the addition of torque arms on each side.
 

Billyrobbo

Finding my (electric) wheels
Jul 17, 2019
7
0
It looks like the motor axle is not deep enough into the dropouts, they need filing so it sits fully in. Also, in my opinion, to fit any hub motor without a torque bracket is asking for trouble. You need something like this:
I,ve used these, they are robust, however they do need something like a mudguard or rack boss to fit to. Otherwise you can use something like this:

Make sure it is the right size for the axle on your motor. As the axle is already spinning I'd say use one either side.
Don't use the bike until you've done this, you could be in for a nasty accident.
Thanks for your help , I have just ordered two of these , I may need some help fitting them though as I have no idea how to use them
 

Billyrobbo

Finding my (electric) wheels
Jul 17, 2019
7
0
It looks like the motor axle is not deep enough into the dropouts, they need filing so it sits fully in. Also, in my opinion, to fit any hub motor without a torque bracket is asking for trouble. You need something like this:
I,ve used these, they are robust, however they do need something like a mudguard or rack boss to fit to. Otherwise you can use something like this:

Make sure it is the right size for the axle on your motor. As the axle is already spinning I'd say use one either side.
Don't use the bike until you've done this, you could be in for a nasty accident.
And how would I fill the drop outs in??
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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Could there be any other reason why the wheel is spinning the axle?
Too much torque for aluminium to hold. On a non-electric bike, there is no torque on the axle, so the drop-outs aren't designed to resist the torque of an electric motor. That's why you need torque arms.

When you install them, don't use the jubilee clips, which break quite easily. Instead, you need to bolt them to a secure point, like a caliper mount, which might require modification of the torque arm tie-bars.
 
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Benjahmin

Esteemed Pedelecer
Nov 10, 2014
2,460
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Could there be any other reason why the wheel is spinning the axle?
Simple physics really. For every action there is an equal and opposite reaction. So as your wheel is driven in one direction, the axle is trying to rotate in the opposite direction and is only resisted by the frame dropouts. As vfr said, aluminium is way too soft to resist this turning moment, so the axle spins and you loose forward driving power.

You don't need to 'fill in' the dropouts. You need to FILE them deeper so that the motor axle sits fully into the dropout. Use a combination of a flat file and a rat tail file.
I suspect that whoever sold you this bike knew there was a problem but didn't know what they were doing.
 

Billyrobbo

Finding my (electric) wheels
Jul 17, 2019
7
0
I installed one of the torque arms and the wheel still come loose soons as I gave it rev , how can I get a torque arm on the side where the wire comes out
 

Benjahmin

Esteemed Pedelecer
Nov 10, 2014
2,460
1,675
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West Wales
But it's a solid axle, if it's still spinning the other side isn't doing it's job. Also that axle doesn't look deep enough into the dropout.
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
19,991
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I installed one of the torque arms and the wheel still come loose soons as I gave it rev , how can I get a torque arm on the side where the wire comes out
Disconnect the motor cable connector, remove the nut shroud and nut. Slide T/A over and along motor cable to fix in place, slide nut and shroud back on, etc , etc.

Axle needs to be a snug fit in to the drop outs and sitting deep enough in the first place with anti rotation washers fitted (these have a right angle tab on them and the tab need so to sit firmly in the drop out), fit a T/A on each side to prevent the heavy D/D motor from twisting out due to torque. How the T/A and wheel axle arrangement is fitted will determine how well the wheel will stay put, for a T/A I always make my own one piece ones out of 2 - 3mm mild steel and fix to an existing tapped hole on the drop out.
 
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