PAS Quite Loose

[Manc44]

This is a 24t Shimano inner chainring, the only size chainring this BZ-10C magnet disc fits to and while it does clip in place, it's quite loose..

The clips holding it on are at about 9 and 3 O Clock:




Clipping it against the notch (that's near 6 O Clock) on the chainring, just bends the magnet disc.

Since it can't be drilled (the 4 points on the chainring don't meet up with anything to keep it held in place that way) I thought about putting 2.5mm wide cable ties around like this, but won't they be hitting the sensor? The cable ties are sticking out by 2mm.

EDIT: This can't work because the Hollowtech 2 bottom bracket cup needs to overlap with the magnet disc and inner chainring, there's hardly any clearance and the BB cup would be interfering with the cable ties.





Here's another PAS I have got, I have got no idea what this one is meant to fit to but I cannot find any way at all this could fit to the chainring, although the magnet disc is small enough to, it's going to be resting on 4 bolts and sticking out a lot itself, also what's the deal with those 3 holes? They aren't spaced around it at equal distances...




Here it is against the chainring...



That one is definitely better quality but I can't see any way to fit it.

When that's resting on the chainring with 4 bolts, it sticks out a mile.

I can't put the PAS on the left side either, there's just no gap there for a magnet disc.

I'm starting to think maybe it's more bother than it's worth trying to do this and to just stick to using throttle only. At least then I could keep my 22t inner chainring too. Of course not using the PAS also means there's no faffing about taking the crankset off either. Now I think I'm starting to like the idea of it not having PAS lol

 

[Manc44]

I think I might have got it to work.

The biggest problem now, would be the cable ties being raised 2mm. The sensor would have to be 3mm or 4mm away to clear them.

The chain doesn't touch the cable tie and the BB cup just about fits there without touching the cable ties.

The blocky clip part of the cable tie can only go where it is now. It can't be rotated around the other side of the chainring because the crank spider arms are going to be there.

"It's a tightrope Spud, it's a f**king tightrope" - Mark Renton

This is one of the tightest squeezes I have ever done on my bike lol.

This was a puzzle where I had to keep the cable ties between magnets, while avoiding the 4 chainring bolts.

Thank god Shimano drilled a load of 2.5mm holes around it for my 2.4mm wide cable ties to fit.

That thing is on solid now... just a mock up of course

There's more of a gap around the BB cup than this photo shows. The chain also looks like it might cut into the cable tie, in reality it can't. It'll be reet!

 

[vfr400]

All the plastic does is hold the magnets in the right positions. You can cut it, drill it, grind it, file it, or whatever you want until it fits as long as you don't touch the magnets. I'd cut off or grind down anything that stops it from fitting right, then epoxy it in place.

Make sure you test it before fitting the disc and refitting the crank to make sure that everything is round the right way. That can save you a lot of work and frustration.

 

[Manc44]

All the plastic does is hold the magnets in the right positions. You can cut it, drill it, grind it, file it, or whatever you want until it fits as long as you don't touch the magnets. I'd cut off or grind down anything that stops it from fitting right, then epoxy it in place.

Make sure you test it before fitting the disc and refitting the crank to make sure that everything is round the right way. That can save you a lot of work and frustration.

Cheers vfr400 you help out so much. I think all I might glue is the cable ties so they are flat to the chainring, hopefully that's all that's needed. Even I can't put this on the wrong way, it's got clips on the reverse side lol

 

[StuartsProjects]

I have a the second PAS disk in your original post fitted (and working!) to the standard 22T inner on an ancient (circa 2002) Shimano crankset.

 

[Manc44]

I have a the second PAS disk in your original post fitted (and working!) to the standard 22T inner on an ancient (circa 2002) Shimano crankset.

If that's an Octalink 2 crank, the BB cup diameter is about 38mm. Mine is a Hollowtech 2 with a diameter of 45mm.

That extra 3.5mm of clearance you have all around, means you can have the cable tie heads on the inside like you've done.

The 12 magnet disc gives about 1mm more clearance all around on the inner hole, compared to the 10 magnet disc.

I'm just noting all this down, not factoring in that these things can be cut/filed etc. Here's the size differences between these 2 magnet discs for anyone reading in future:

10 Magnet disc (BZ-10C):
Outer diameter: 78.0mm
Inner diameter: 46.6mm
Height when resting on bolt heads: 5.4mm
Sensor edge from metal BB ring: 3.9mm

12 Magnet disc
(has "2" stamped in it and 3 holes, sensor has FOREN15194, with red LED):
Outer diameter: 77.9mm
Inner diameter: 48.7mm
Height when resting on bolt heads: 8.0mm
Sensor edge from metal BB ring: 3.0mm

The 12 magnet version sticks up 2.6mm more, thus putting it closer to the sensor, but the sensor that comes with sticks out 0.9mm less. If I have worked it out properly then the 12 magnet setup creates a gap 1.7mm narrower to the sensor.

Assuming a Hollowtech 2 setup, whether the sensor needs bending a bit depends on what spacers people are using on their BB cups. The drive side typically has 2.5mm worth of spacers there (a 0.7mm and a 1.8mm together) so, sandwiching the sensor ring in 3 different places is possible - right up against the BB shell, between the spacers, or on the outside between the last spacer and BB cup lip. I can only see it fitting up against the BB shell though, it's tight down there lol.

 

[StuartsProjects]

I did remove the inner ridge from one side of the 12 magnet disk, then it fitted down tight to the bolts on the 22T ring.

 

[Manc44]

Now I have seen that fits into a 22t I might try to work out a way to use it.

On your first pic it looks like there's extra metal tabs where the 4 bolts go into the crank arm?



On mine there's no metal after those 4 holes on the crank arm, it's like this:



Another thing is, my 22t chainring doesn't have holes drilled in it like the 24t does, so I'd have to drill holes to fit cable ties to it.

The only problem left is the cable ties sticking up where the magnets are. There's only about a 6mm gap from the top of the bolt head to the BB shell and the magnet disc + cable ties wrapped around + a gap + the sensor all have to go there!

From the magnet side of the disc to the top of the bolt heads, the thicknesses are:

10 magnet disc: 4mm.
12 magnet disc: 6mm.

It can't work on the 12 magnet disc because the thickness of that alone is 6mm. The inner plastic ring that sticks up would need taking off. Then it would only stick out 3mm, which is 1mm less than the 10 magnet disc. Combining that with the 12 magnet sensor also having a gap 0.9mm bigger means the 12 magnet disc has a gap 1.9mm bigger, over the 10 magnet version.

I'd need to cut that lip off completely:



Then the bolt heads might be pushing directly on the magnets though.

What I can't understand is why they don't just supply these discs with 4 recesses in them for the 4 bolts at 64 BCD, so the magnet disc rests flush with the chainring.

Another way then is to only cut out gaps between magnets in the recess, where the 4 bolts heads are. This doesn't close the 6mm gap down to 3mm though (like fully removing the sticky out bit would) - it only creates a gap bigger by the thickness of a bolt head.

I think I'll just try to use the 10 magnet disc, but from what I can tell, if it has cable ties around it, there's an overlap of about 2mm between the cable ties and sensor, because the sensor sticks out 4mm from the BB shell, and I know there's a 6mm gap there in total - leaving only 2mm to play with even before a magnet disc is added. I have no idea how this is going to work then lol.

What I need is a spare HT2 crank arm to test it on a spare frame/BB/chainring but I haven't got another crank arm sigh.

 

[StuartsProjects]

Another thing is, my 22t chainring doesn't have holes drilled in it like the 24t does, so I'd have to drill holes to fit cable ties to it.

Indeed, my 22T had small tabs opposite the fixing bolts, which I did drill 3mm holes in to take the cable ties, use a hard drill.

 

[Manc44]

Oh right that's on the chainring itself, not the crank arm, my bad.

My chainring has got those, but there's not much spare metal there. Drilling holes there so close to the chainring bolt holes, I dunno about doing that, it might make it weaker where it's bolted, especially being such a small chainring with more torque compared to a bigger chainring - but then again with it being on the inside of the bolts and not the outside where all the pedalling forces are, I can't see how drilling anything there would be a problem, nothing is being made weaker... I think.

I just looked at my bike and there's about 2mm of space between the 4 bolt heads and the edge of the BB cup. They overlap into the BB cup about 80% of the way into it.

Unless I use something like one of these, a 2.5mm x 24mm ID spindle spacer, there's no way to create a gap big enough there. That's going to throw the chainline out to 52.5mm though, beyond the 50mm where it is now. Whether that would affect shifting much, I would only know by trying it. To think this is one of the reasons I avoided a mid-drive setup hahaha.

Going off a mock up I have done, the chainline needs to be increased by about 2.5 if using the sensor that pokes out a bit more, but with the other sensor, it would only need spacing out 1.5 more. That's more like it. Just by using the sensor that came with the 12 magnet disc I can gain 1mm on the gap.

I've already got 1mm spindle spacers from past fettling so it's all doable.

This is all before any sensor bending goes on which I am trying to avoid doing!

 

[StuartsProjects]

I did use a BB spacer, you can see it in the picture, its between the frame and the metal bracket of the PAS sensor, 1.5mm.

I also gained just over 1mm by bashing the bends in the PAS bracket square in a vice.

 

[Manc44]

Cheers StuartsProjects.

I modified the 12 magnet disc by cutting away the areas where the bolts are, so the disc now sits flat on the 4 chainring bolts.

Miles better now