Hollowtech crankset and PAS

I converted my 2016 Specialized Crosstrail Expert bike to an ebike a year and a half ago. I have both a PAS and a thumb throttle. The thumb throttle is just a back up since I have had issues off and on with the PAS over my time riding the bike. I love the PAS and prefer to use it that way but here are my issues...

I have a dual chain ring setup on the front and more than a few times my chain has skipped off on the inside and one of the following has occurred...
1. chain slides down between the PAS ring and the sensor on the downtube pushing it back so it no longer senses the PAS ring magnets. Fairly easy to fix.
2. chain slide down and gets between the PAS ring and the small chain ring, less common but has happened, which causes the PAS ring to break off. Lost one half of the PAS ring once. The second time I did manage to recover both pieces. This most recent time I still recovered it but additional issues need to now be sorted out.

In mounting my PAS ring, I wasn't able to get it to stay put using just the magnets. I did change my chain ring bolts to steel but it always wants to shift and I go over some bumpy areas on my commute so I didn't think it would be sufficient to do it that way. In the end, after doing a bit of searching online, I decided to use some JBWeld and glued the PAS ring to my chain ring bolts. That worked fairly well after my second attempt at gluing it and has been working for over a year. The downside is that I recently mangled my small chain ring and need to replace it. Since I glued it in place, it was a pain to get it cleaned up enough to get the bolts out to remove my chain ring.

I am wondering if anyone has figured out a better way to mount a PAS on a hollowtech style crank set? I would really like to do the PAS on the left side but there is no way to make it work from what I can tell. I would prefer not to have to glue it again if I can avoid it. What are you all doing to get it mounted securely?

Thanks,
Rob

For left side mounting, you could core out the PAS magnet ring just large enough to friction fit over the hollowtech crankshaft, and if there's no place to mount the PAS sensor ring on the left side, simply take the sensor off it's ring and clamp it to the frame (zipties, etc) close enough to the PAS magnet ring to pick them up as they pass. You might have to make a bracket out of easily-formable metal or plastic, or even cut up the oriignal mounting ring if necessary.

The kingmeter DH 12 Pas Ring + Sensor ist designed for hollowtech cranks. I have one on my carbon bike, and it fits perfectly. I had to swap the smallest chainring for a steel one though, for the pas ring only uses magnetic force to hold onto the chainring. For the sensor, I cut a custom 1.75mm piece of aluminium which I screwed beneath the BB, using the same bolt hold that cable routing bracket.

My Fatbike has a similar Crankset to the one you have.
I am using a KT Kunteng KT-D12L PAS KIT, which is specially designed to be mounted on the left side crank. The 12 magnet ring is in 2 parts, and held together after fitting on the crank with a large spring steel clip.
I have been using it for 2 years and it has worked faultlessly. You can find this part for sale on many stores on Aliexpress, which is where I sourced all my KT Kunteng conversion parts.

Johne-bike said:

My Fatbike has a similar Crankset to the one you have.
I am using a KT Kunteng KT-D12L PAS KIT, which is specially designed to be mounted on the left side crank. The 12 magnet ring is in 2 parts, and held together after fitting on the crank with a large spring steel clip.
I have been using it for 2 years and it has worked faultlessly. You can find this part for sale on many stores on Aliexpress, which is where I sourced all my KT Kunteng conversion parts.
IMG_20170305_150745.jpg

Click to expand...

Did you have to leave space between your BB and the crank arm for that to fit on the left side? Or does it fit overtop of whatever is there? I did find the part on Aliexpress and will order one to give it a try but I wouldn't mind knowing a bit more about how you got it to work. I am not looking at my bike at the moment but I think the crank arm buts right up against the bottom bracket if I am remembering correctly.

You are correct in that the crank arm fits tight against the bottom bracket and bearing, and if like mine there is also a hard rubber dust seal between the two.
You do need to move the crank arm out a few mm's on the shaft to accommodate the magnet ring. To minimise the amount I needed to move the arm, I reduced the thickness of the "plastic fingers" on the magnet ring by about half, using a sharp scalpel blade. They are quite easy to cut, and still retain plenty of strength and purchase on the shaft when cut.
I also had to trim the length of each "plastic finger" to enable the magnet ring to fit over the large diameter of the crankshaft, yet leaving them long enough to continue to grip tightly. All this was only an hour or so of work, and the end result was that I could retain the original dust seal, and leave sufficient shaft for the crank arm to bolt up securely.
I have used the bike for over 4000kms, and nothing has come loose, or given any problems whatsoever. It is so much neater and simpler than trying to fit a magnet ring on the right side, as you know!

You are correct in that the crank arm fits tight against the bottom bracket and bearing, and if like mine there is also a hard rubber dust seal between the two.
You do need to move the crank arm out a few mm's on the shaft to accommodate the magnet ring. To minimise the amount I needed to move the arm, I reduced the thickness of the "plastic fingers" on the magnet ring by about half, using a sharp scalpel blade. They are quite easy to cut, and still retain plenty of strength and purchase on the shaft when cut.
I also had to trim the length of each "plastic finger" to enable the magnet ring to fit over the large diameter of the crankshaft, yet leaving them long enough to continue to grip tightly. All this was only an hour or so of work, and the end result was that I could retain the original dust seal, and leave sufficient shaft for the crank arm to bolt up securely.
I have used the bike for over 4000kms, and nothing has come loose, or given any problems whatsoever. It is so much neater and simpler than trying to fit a magnet ring on the right side, as you know!