DIY alternatives to the sprocket rag joint?

Discussion in 'Hubs, Gearboxes, Sprockets and Chains' started by gobigkahuna, May 6, 2011.

  1. gobigkahuna

    gobigkahuna New Member

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    I'm looking to convert a bike with 48 spoke wheels so the standard 9 bolt rag joint won't work. the hubs are coaster brake styled, but I plan on disabling the coaster brake and using caliper brakes instead. Any DIY solutions that mechanically connect the sprocket to the hub without buy an expensive adapter or new hub?
     
  2. Mac

    Mac New Member

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    Check with Sportscarpet, he makes adapter with a 3.75 centerline, I have the same bike as you, I made a template out of paper, 3 point on that same circle, 120 deg apart, the hub on the Oynx is 1.519",within .004 of a CB110 hub, with my initial measurements and template, looks like his will work. I didn't order it yet($$) but a 50tooth sprocket will make up for the extra rollout of the 29" tire,{same as a 44with a 2 stroke} (if you have the 5:1 hoot gearbox),If you have a different gearbox, like a 3:1,let me know, I'll let you know the right sprocket size to keep the motor in the right RPM range. Mine has the 5:1gearbox and a 10to 44T final and its too tall, over 50 on a long downhill, bout 22 on level ground
     
  3. gobigkahuna

    gobigkahuna New Member

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    @Mac - Do you have a link to Sportscarpet handy? I googled it and couldn't find it.

    Edit: Never mind, found it here: http://motorbicycling.com/f23/sprocket-adapter-sportscarpat-26938.html The only price I've found was $80 for the CB110 with a 40t sprocket. I wonder what it would cost for our hub + a 56t sprocket (I'm more interested in hill climbing power than speed).

    So you're sure the 120degree mount spacing will clear the spokes? What about chain clearance? I've read that can be an issue with these. I plan on removing the coaster brake on mine and adding front and rear calipers.

    The other direction I was thinking about was a diy jackshaft. I haven't seen too many attempts at it, but am only just starting my homework on the topic.
     
    #3 gobigkahuna, May 7, 2011
    Last edited: May 7, 2011
  4. DuctTapedGoat

    DuctTapedGoat New Member

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    Pirate cycles sells the clamshell adapters. HybriPed might work too. Myself, I've been on disc hubs, mounting the sprocket to the rotor mount, and I love it.
     
  5. gobigkahuna

    gobigkahuna New Member

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    The min inside diameter for the Sportscarpat / Pirate cycles adapter is 1.522" while the hub diameter is 1.519", that's a 0.003" difference which isn't much but enough to keep it from working I'm guessing. I suppose a shim could be used, but it would have to be -real- thin, eh? I've sent an email to Sportcarpat but haven't received a reply yet. Failing that my alternatives look like they will be to either force the rag joint to work or get / build a jackshaft.
     
  6. DuctTapedGoat

    DuctTapedGoat New Member

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    Well, you can always recut a larger circular hole in the center of the sprocket.
     
  7. gobigkahuna

    gobigkahuna New Member

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    Not sure how that would help. The sprocket adapter mounts to the body of the hub. My hub is 0.003" smaller than the sprocket adapter is designed for, so the adapter would likely slip. How would enlarging the center hole of the sprocket help?

    I did look at the HybriPed site and I'm pretty sure that won't work, the holes for the mount looks like it's specifically designed for a 36 spoke wheel. It did give me an idea though, if I can locate a 50-56 tooth sprocket without the 9 bolt hole pattern, then I can drill my own holes. I'd have to make my own backing plate (do-able) and rubber rag backing (not sure if that's do-able) though. The other thing I noticed about the HybriPed is that it uses a lot more bolts to secure the joint. Looks considerably more secure than the standard 9 bolt pattern.
     
  8. DuctTapedGoat

    DuctTapedGoat New Member

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    Oh, sorry. I was thinking you couldn't fit the hole over the flange.

    For true DIY you could drill through the flange and sprocket, tap it and bolt your sprocket to the hub.

    Though - you really don't need the plates from the rag joint. You could easily drill out a different hole pattern and make your own custom rag to fit, using washers to replace the plates.
     
  9. gobigkahuna

    gobigkahuna New Member

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    Yeah, I saw a build where he did that. I like that idea, but I don't think the hub has enough room for me to do that. I'll have to check it though.

    Do you happen to know what the rag material is and where I can get some? I've not seen one in "real-life" but I'm guessing it's some sort of reinforced rubber (like sidewalls material on a auto tire)?
     
  10. DuctTapedGoat

    DuctTapedGoat New Member

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    Gotta be sure you don't hit the bearings of course, it's tough to say without seeing. If it's an oversized flange with a small hub, you might be able to.

    I was talking with a friend a while back about using old conveyor belt material. Tire material I think would work if you could get a good large solid piece of it.
     
  11. gobigkahuna

    gobigkahuna New Member

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    I don't have the bike at the moment (waiting for a replacement bike that should be here this week) but if I recall correctly, it's a big hub'ed coaster brake style and the flange was pretty small. With 48 spokes it looked pretty tight. When the new bike comes in I'll give it another look.

    I'll check McMaster Carr, they carry everything. ;)
     
  12. gobigkahuna

    gobigkahuna New Member

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    I just checked at McMaster Carr and they carry shim material in .001 / .002 / .003" thickness, so that might be one solution. I'm waiting to hear back from Sportscarpat, but I'm hoping this might work.

    Another solution, albeit a lot more work, is shown here: Rear Hub Sprocket Mount - MotoredBikes.com: Motorized Bicycle Forum (My appologies for the cross link to a different forum, but it's relevant to my question.)
     
  13. docimastic

    docimastic New Member

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    SOLVED: mount 9 hole sprocket rag joint on 48 spoke wheel

    I KNOW this is an old thread, so please don't yell at me for adding to it. Maybe I should have made a new post?
    Just built a Genesis GX7 ("29er" 48 spoke wheels) motorized bicycle using the rag joint with 9 hole sprocket. The trick is to use only 6 of the holes. Two bolts in adjacent holes, skip a hole, two more, skip a hole, and then two more. Lay the wheel flat and try a few different positions. It CAN be positioned so the bolts drop right through the spaces between the spokes with the sprocket perfectly centered.
    One other thing... the "1/3 moon" plates will bend, unless a second set is added. I happened to have on hand both the "1/3" plates and the older style "1/2 moon" - 4 holes in one plate, 5 in the other - and used those in conjunction with the 3 hole plates. Not having tried it, but it seems that it should be fine if all the 3 hole type... if the second set is staggered in relation to the first.
    Hope this helps someone!
     
  14. cannonball2

    cannonball2 New Member

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    The rag joint has improved a bit over the years, The early ones had thinner backing plates compared to the ones I'm getting now. Also the sprockets with the slotted holes seem to align better maybe having a bit of float to line up. They must have changed the sprockets center hole also. I haven't had to grind a center hole to fit a coaster in a long while. The instructions call for no plates against the sprocket now.

    I find retightening the joint several times a few days after installing seats them really well. All in all I can now live with them on all but a bigger HP/hi torque build.

    BTW if you are building a cross over RH drive the common CG sprocket will bolt directly to an 18t coaster and centers well on the sprockets boss.
     
    #14 cannonball2, Jan 9, 2017
    Last edited: Jan 9, 2017
  15. docimastic

    docimastic New Member

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    Thanks for your thoughts, cannonball2. I am a newbie to motorized bicycles - although I am now doing my 6th kit installation, so I can't comment meaningfully on the apparent changes you talk of. I have only built one with a coaster brake; didn't have to grind open the sprocket center hole, but did have to trim the outer circumference of the dust cover, and bend the brake arm.

    Getting the sprocket installed and concentric with little lateral run-out always takes me more time (at least it seems) than installing the rest of the kit! I DID order a sprocket with slotted holes and will see if that does in fact allow more or easier adjustment to getit concentric with the axle/ hub.

    One problem I've run into is that the rubber pads often vary in thickness....on each pad (not one compared to the other - that is not an issue) even though it appears they run them through a machine that is supposed to grind them to make each uniform in thickness around its circumference.

    My biggest question regarding installing the rag joint bolts and nuts is how tight is tight enough? How tight is too tight? Plus it seems that to reduce wobble, some have to be looser than I'd like, and some tighter than I'd like. Have never used a torque wrench....

    Any thought on proper torque on the rag joint bolts?

    Thanks......

    David
     
  16. cannonball2

    cannonball2 New Member

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    I just swapped sprockets on my current build and went from a dished to a flat sprocket. I had added plates under the dished to align it. On the flat I had to remove them. This caused the inner rag to have to be pulled in closer as the sprocket bottomed on the wheel hub a bit early. I just kept tightening until it all pulled together and ran true(or very very close). I tighten until all bottoms no set torque. You just have to work with it to get it true, like spoking a wheel.

    You have to be careful not to load the spokes excessively laterally(bending toward the sprocket) however I never leave any gap between the rags. Its the firm bottoming of the rags into the spokes that handles the drive loading. Too little and it will spin and remove spokes for you! I also would advise tightening a few times over a day or two after installation, and checking on regular intervals as maintenance.

    Properly done the old rag joints not to bad.
     
  17. docimastic

    docimastic New Member

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    Hi, cannonball2! Sorry for my late response to your comments (thank you!)

    First, I have to agree about "Properly done the old rag joints not to bad." Look at the numbers (no, I don't actually have the numbers, but.....). I have to believe that probably 99% of the tens of thousands of motorized bikes use the rag joint. Yes, I would love to use a sprocket adapter instead, but they are simply cost prohibitive for me, whether for a build for my son and me, or for re-sale. 50-80 percent of the cost of the complete engine kit!

    Interesting about having added plates under the dished sprocket. Did the plates contact the spokes? I would be concerned about that...concerned that the metal would cut into /cut / weaken the spokes.

    Yes re loading the spokes excessively ... hence my "how tight is tight enough" question. Too funny saying "too little and it will spin and remove the spokes for you".

    I have not yet had a build where the sprocket bottomed on the hub..which, at least in theory, would seem to help lateral ("wobble") alignment...but it would also limit the force of the rubber pads on the spokes - which as you discuss, must be tight enough to fully "grab" the spokes. FYI, I use a dial gauge to check the lateral runout... the best I can consistently achieve is about 0.020 inches...roughly 0.5 mm. I am convinced that the sprockets that come with the China Girl kits are not completely flat... that is, they have their own "built in" wobble /bend. Grrrr I also suspect that the toothed circumference of some or even most is not a true circle (meaning having a slightly flatter area) which makes it impossible to maintain consistent play in the chain (while rotating the wheel and sprocket) while setting the tensioner. I did use a spring loaded tensioner (the one sold by turbobuick1 on Ebay) on a build for personal use. The tensioner is a beautifully engineered and manufactured piece, and works great - despite my concerns about the top / drive side of the chain loosening when starting or backing off the throttle ... but, again, using this adds just over $40 to the cost of the build.

    Good advice (thanks!) about checking the tightness of the rag joint on regular intervals as maintenance, and especially a few times after the initial install...as the rubber compresses where the spokes contact it.
     
  18. cannonball2

    cannonball2 New Member

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    I agree on the poor execution of the stock sprockets. I have had some where the teeth were not in the same plane. That's a major chain thrower. I aligned them with a rawhide hammer only because I need to run a BMX chain and it required a thin sprocket. Other wise I would have canned it.

    The current build has a really weird flip flop wheel that required spacing an offset sprocket to get the chain line. I added a set of plates between the sprocket and rag. When I changed ratio All I could find was a flat sprocket that required removal of the plates. This really put the rag to the test as now it had to pull both rags closer to clamp properly. The outer rag had to come in more. It finally bottomed and aligned very true and has held so. Just shows the flexibility of the system.

    Your .020 run out is not bad. The spring loaded idler easily handles that. The upper chain run should not loosen overly as the slack is constantly taken up by the idler. I would have to give some hands on but gut says the slack that may exist is gone in half a revolution, certainly by one. I cant over state the effectiveness of a chain loaded idler. If you use the base clamp that comes with a CG kit you can easily make a system using a short piece of flat stock, a spring and a clamp to anchor the spring for basically no $$.
    I'm fond of mounting the stock clamp under the engine when possible. Here a link to the current build with an idler made from a side pull brake caliper. It has actually been trimmed down a bit now.
    http://motorbicycling.com/showpost.php?p=648696&postcount=40



    I think with a good understanding the system it works very well for most builds.


    .
     
    #18 cannonball2, Jan 21, 2017
    Last edited: Jan 21, 2017
  19. TheNecromancer13

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    In terms of the sprocket adapters being too expensive, you might want to consider making your own. If you use a rear wheel with a disc hub, all you need is a piece of quarter inch steel plate, use a 3 1/2" (or similar size) hole saw to cut out a circle of 1/4" steel, drill out a hole for the bike axle (with a small hole saw), drill 6 small holes for bolts to the disc brake hub, and then whatever bolt pattern you want to mount the sprocket to the steel plate. Use washers as spacers to get proper sprocket alignment. I have done this on a build for a friend who was worried about cost, and it worked great! Just be sure to paint it or it will rust.

    BTW, you are correct about the stock sprocket not being flat, I had 2 of them lying around unused, and after reading your comment, I got out my surface plate and laid the sprockets on it, neither of them was anywhere close to flat, and they were both never used. One of them had about a quarter inch of variation!
     
  20. ultralight01

    ultralight01 New Member

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    That's because they're stamped...
     

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