Help! How to mod Cyclotricity PAS rotor?

Geoff_L

Finding my (electric) wheels
Mar 16, 2014
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Thanks to help from this forum, I've manage to convert my wife's bike using a Cyclotricity front hub kit and I'm now trying to do the same with my old hybrid. However, I have one outstanding 'gotcha' to resolve:- the PAS rotor (see piccy) as supplied doesn't fit the bottom bracket spindle -- even though the exposed section of the spindle is within OEM specs (see piccy). The exposed portion of the BB spindle is 2.1mm (see piccy) but the PAS rotor is 4mm thick!

The 'hole' in the centre of the PAS rotor is ~32mm dia and the 'inner spigot' of the crank on that side is ~30mm dia x ~3mm wide. So my gut feeling is to remove all but 1mm of each 'finger' in the PAS rotor centre hole and then glue the rotor to the crank using epoxy. However, I suspect that someone might have modified one of these rotors and might have a better idea. Hence words of wisdom from the forum will be gratefully received.

Thanks for looking. Geoff

PAS_GA_01.jpgPAS_GA_02.jpgPAS_Rotor.jpgOEM_Graphic.jpg
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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It's OK to grind 3mm off the inside of the pedal arm. The other thing you can do is get a longer BB - about £10 in Halfords.
 
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Geoff_L

Finding my (electric) wheels
Mar 16, 2014
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It's OK to grind 3mm off the inside of the pedal arm. The other thing you can do is get a longer BB - about £10 in Halfords.
Thanks. I had considered cutting off the 3mm 'spigot' from the crank but the guy that runs my LBS tells me the crank is likely to move further onto the tapered square of the BB spindle, closing the gap to below 4mm, if I do :( He also tells me that. because it's a sealed BB, getting a longer one will move the drive-side crank further out but that BB design has the non-drive side clearance fixed. FWIW, I'd also considered shimming the tapered square, thus causing the crank to move outward -- but I suspect modding the PAS rotor might be easier! Thanks again, Geoff
 

vfr400

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Jun 12, 2011
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Thanks. I had considered cutting off the 3mm 'spigot' from the crank but the guy that runs my LBS tells me the crank is likely to move further onto the tapered square of the BB spindle, closing the gap to below 4mm, if I do :( He also tells me that. because it's a sealed BB, getting a longer one will move the drive-side crank further out but that BB design has the non-drive side clearance fixed. FWIW, I'd also considered shimming the tapered square, thus causing the crank to move outward -- but I suspect modding the PAS rotor might be easier! Thanks again, Geoff
He must be a thicko. The size of the rest of the arm doesn't change, so how can it slide up the taper. Grinding 3mm off is a standard bodge done by several of us on this forum.
 

Geoff_L

Finding my (electric) wheels
Mar 16, 2014
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He must be a thicko. The size of the rest of the arm doesn't change, so how can it slide up the taper. Grinding 3mm off is a standard bodge done by several of us on this forum.
Thanks. FWIW, removing the 3mm seemed a good option -- but he did seem to speak from experience. That said, I don't think he has much experience of eBikes and so hasn't had any call to perform such a mod. I haven't got a grinder -- but my trusty hacksaw and selection of files will be employed tomorrow!
Thanks again, Geoff.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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Basildon
Thanks. FWIW, removing the 3mm seemed a good option -- but he did seem to speak from experience. That said, I don't think he has much experience of eBikes and so hasn't had any call to perform such a mod. I haven't got a grinder -- but my trusty hacksaw and selection of files will be employed tomorrow!
Thanks again, Geoff.
He tried to use logic, but his brain couldn't visualise what's going on. Imagine it as it is now. E whole of the taper in the pedal arm is in contact with and hjammed against the tapered spindle. If you could remove a couple of mm from the inside face without removing the pedal arm, the remaining 90% would still all be jammed against the spindle. How could it move? Don't grind off more than you need to.
 
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Geoff_L

Finding my (electric) wheels
Mar 16, 2014
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A quick reply for completeness. I've removed about 2.5mm from the inside of the non-drive-side crank and the PAS rotor now fits perfectly. Unfortunately, the front mech clamp prevents attachment of the sensor to the seat tube and there isn't enough space between the rotor and the down tube to fit the sensor as supplied. However, the sensor comes with a bracket that effectively doubles its thickness and the sensor should fit if I remove the bracket and the lugs on the sensor body and then stick the sensor in place on the down tube with double-sided tape (and hold it in place with a cable tie for security).

Thanks to all for the help. Geoff

39401
 
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