magnetic disc problem

josh kayz

Finding my (electric) wheels
Dec 25, 2019
9
0
Hi,
I`m trying to convert an old rockrider bike,from decathlon, but i`m having a problem with the magnetic disc, it will go on , and when i i turn the pedals it works for pedal assist mode, but the problem is when i tighten the pedal back on about 50% the disc stops moving,and the pedal arms become stiff to move, not sure what to do? i thought washers but i`m not sure that will work, i`ve converted other bikes never had this problem.
Josh
 

Woosh

Trade Member
May 19, 2012
13,269
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Southend on Sea
wooshbikes.co.uk
check that you have enough space between the crank and the bottom bracket's face.
If your bottom bracket has external ball bearings, you need a drilled disc.
Post some pictures.
Which bottom bracket do you have?
 
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josh kayz

Finding my (electric) wheels
Dec 25, 2019
9
0
thanks for the reply woosh,i dont think theres enough space ,any way round that?
 

Woosh

Trade Member
May 19, 2012
13,269
10,421
Southend on Sea
wooshbikes.co.uk
you can file off some from the crank or if you have a square taper bottom bracket, replace it with one that has a longer axle.
If your bottom bracket has external ball bearings, you need a drilled disc.
Post some pictures if you want suggestions.
 
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Kwozzymodo

Pedelecer
Sep 9, 2017
113
16
58
Lincolnshire
I usually enlarge the hole in the centre of the disc until it sits nicely on the inner chainring. Sometimes the disc stays magnetised to the chainring, but I usually epoxy it in place. You can then fully tighten the crank onto the axle without the disc binding on the sensor.

Longer axles might work, but you are then potentially dealing with chainline issues and the Front derailleur not capable of pulling the chain onto the outer chainring due to the longer axle moving the chainset further outboard.
 

josh kayz

Finding my (electric) wheels
Dec 25, 2019
9
0
hi thanks for the replies, that seems a decent idea kwozzy, how are you enlarging the hole in the center of the ring though?
 

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
7,845
5,779
The European Union
Decathlon seem to prefer the absolute shortest bottom brackets for some reason. Dremel is your friend!

I put a disk on the left hand side and to make it work I cut the centre of the disk out and mounted it to an adaptor cut from the bottom of a coffee can - more or less 4,500 km later there is a bit of rust but other than that it still works.
 
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Kwozzymodo

Pedelecer
Sep 9, 2017
113
16
58
Lincolnshire
A hole saw might work, but you will need to hold the disc very firmly - screw it into a block of wood before drilling. I use a Dremel and sand out the hole. Takes about ten minutes.