6-bolt 44BCD to 4-bolt 104BCD Double supported Top Hat, for 135mm O.L.D. Disc Brake Hubs

FurryOnTheInside

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The more I think about it I have to ask since I don't know your exact set up. I believe the split plate will stop you from getting enough offset on the sprocket. Most I have seen need the sprocket inboard of the back of the rotor flange. Yours will be almost directly over it.
I have a few options. This system should leave the door open/ bridge unburned to a few options anyway.

In the coloured sketch (which I really did for my own benefit so it may be confusing!), I have shown an alloy chain guard outboard of the split adapter (lined up with the inside of the rotor flange) with the chainring inside of it, and the split adapter narrowed fron the inside edge to make it 3.5mm thick.
On the black sketch I changed things a little. I showed the split adapter narrowed from the outside edge, so the two rings are moved inboard by 1.5mm compared to the previous sketch.

I'm not sure the 1mm gap between the split adapter and the spokes will exist in real life when I try to assemble it.
I don't even know if I'll be able to reach the heads of the m10 button head Allen bolts but we'll see! :)
 


FurryOnTheInside

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I got my rear wheel on and able to turn today. I had to change my design very slightly due to a chainstay clearance issue. The flanged nuts were just too thick. Pity, because they gripped the alloy spider really well.
I also had to make some changes to the m10 bolts too. They needed to have flatter heads on two of them because I'm using four on a 36 spoke wheel and two of them ended up right over a spoke, and the angle of the spokes won't allow a normal button head to fit between the sprocket and spokes. The other two were fine because they fit just between the spokes.
After grinding down the bolt heads and getting the thin (about 5mm thick) m10 nuts I still found I had to shorten the bolts. I wasn't going to wait for new bolts especially as I'd already spent time grinding the heads down, so I shortened the bolts by grinding (at a slight angle) after the final assembly with blue loctite.

Other things that needed some refinement.. the split spider needed it's inner edge grinding back slightly (the waist of the hub was a little wider than I thought) and rounding off to be able to wedge between the rotor flange and the spoke flange.

I did of course decide to add the four extra m5 bolts through the arms of the spider, as gary55 mentioned above. :) Shown here as the blue m5 bolt, with the other changes labeled.
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Even with the thin nuts and the ends of the m10 bolts ground off there is very little space between them and the chainstay. I even ground a little bit off the nuts. The bolts spark a hell of a lot more than the nuts and I'm a little deafer now. :) I'm very glad that I didn't try to build this as a five bolt 110mm BCD as that would never have fitted on the Sirrus frame.
_20170810_155112.JPG


In the final assembly the split spider is ground down to 3.5mm thick to keep the spacing of the two sprockets the same standard as normal SRAM front sprocket indexing. It is fairly flat but nothing special just done with a very brutal but cheap rotary tool burr and a file. And a digital caliper. :) So it's cheap, except for the two little alloy plates.
I am going to use the bike as a single speed, the outer sprocket is just for extra rigidity. Just wanted to leave bridges unburned. ;)
_20170810_155031.JPG

_20170810_155057.JPG


Time will tell, but this feels very solid indeed. :)

_20170810_155014.JPG
 

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CrazyDan

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Put 2 sprockets on a jackshaft lined up perfect with the 2 on the rear wheel, just make sure the front+rear tooth count of both sets are equal and you can swap the chain in 30 seconds for gear ratio adjustability on the side of the road just popping the master link and moving the chain over.
 

FurryOnTheInside

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Put 2 sprockets on a jackshaft lined up perfect with the 2 on the rear wheel, just make sure the front+rear tooth count of both sets are equal and you can swap the chain in 30 seconds for gear ratio adjustability on the side of the road just popping the master link and moving the chain over.
Perhaps even no need to pop the master link if the tensioner pulley is movable! But anyway it would require three sprockets on the jackshaft and the way I have it set up now my inner (42T) sprocket is lined up with the engine sprocket so the 42T would need to be moved outboard several mm for it to line up with a JS sprocket. That then might cause issues with chain-chainstay clearance.
So perhaps it's workable on a wider frame like with more U (cruiser) shape rear stays, rather than V (MTB) or trumpet (roadie). The Sirrus is fairly trumpet shape.

As my rear sprockets are sized for 3/32" multi speed chain, I would like to be able to just run directly from the engine sprocket. But I don't have to get into that just yet. For now I have to get this bike rideable with 1/8" chain and find out whether my sprocket mount is even strong enough for the job.
 
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Tim K.

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Oct 28, 2017
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Where can I get an Adapter that's in the first Photo? I've been looking all over the WWW until I got here. This is exactly (I think) what I need.
Thanks Tim
 

FurryOnTheInside

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Where can I get an Adapter that's in the first Photo? I've been looking all over the WWW until I got here. This is exactly (I think) what I need.
Thanks Tim
The one in post #2 ? I really don't know. I think it was made as a one-off for an e-bike by someone who has access to a CNC machine.
That's why I asked someone on eBay to make one for me, but when he let me down I had to make something myself that does pretty much the same job.
Anyway the amount of offset on the pictured offset 5 arm spider appears to be not enough to line up the rear sprocket with the front sprocket on the 2-stroke Chinese engine, if you use it on a standard 135mm O.L.D. hub. It would require some spacers to be used between it and the sprocket to get the sprocket a bit further inboard.
 
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curtisfox

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May be a little late but one could of dimpled the frame inside, to clear................Curt
 

FurryOnTheInside

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Oh great it deleted my entire update/ self reply.
It wasn't that interesting to read anyway.
Just annoying to lose what I had typed. Its so hard to type on a smartphone already. 🙄
 
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