magnetic disc problem

[josh kayz]

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]

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?

 

[josh kayz]

thanks for the reply woosh,i dont think theres enough space ,any way round that?

 

[Woosh]

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.

 

[Kwozzymodo]

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]

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]

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.

 

[D C]

you can file off some from the crank

That worked fine for me.
Dave.

 

[Kwozzymodo]

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.