Multispeed solution?

Discussion in 'Performance Mods' started by KeepOnKeepnOn, Nov 28, 2007.

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  1. I was doing some research on jackshafts, looking for a way to transfer power to the right side with the intent of using an internal geared wheel hub. I stumbled upon a 2 speed jack shaft that uses a clutch system to switch between 2 different sprockets. I checked the archives but couldn't do a proper search. It poses some problems:
    1. it operates with 2 sprockets on your rear wheel and 2 chains going to them from the jackshaft. Not a big problem but heavier, more expensive, noisier and harder to pedal.
    2. Now the jack shaft has moved you to the right side of the bike and you want your drive to be on the left.
    Anyway, I haven't worked out how to use it bu was sure it would be of interest if it has not already been used. search for jackshaft

  2. Thanks for the post....Had no Idea something like that existed....I did read the
    info on one of the jackshafts and it seemed to indicate the presence of a centrifical clutch....that may present a problem for a "happy time" engine since it may not allow for bump starting but it may work (with some mods) on a rack type system....It would be neat to learn how they brain can't figure it out without a video or diagram...Good post

    Oh....welcome to the forum!
  3. Thanks for the welcome, I've been lurking around reading posts and figured I'd join in when I found this jackshaft. Found a lot of inspiration in the bikes I've been checking out.
    I forgot all about the bumpstart problem because Ill be using a pull start 4stroke with a centrifugal clutch of its own.
    This thing is built on a 8.5" wide 5/8" shaft, the drive gear it comes with is 12 tooth (looks easily switchable) it then switches back and forth between a 12 and a 24 tooth (maybe changeable), #35 chain. So when it switched gears the tooth number on the drive would double.
    Possible ideas:
    1. It may be too much gear to keep the whole works on the same side, but if you could keep it all on the left with out ever crossing over you'd be set. Might have to put the motor way off to the left to align the chain.
    2. If you had a multi cog type wheel (mountain bike type), perhaps you could put #35 gears on the first 2 then regular bike chain gears for the rest, but then your cranks would spin. Or put bike chain gears on the jackshaft, but same problem with the cranks. Might be able to get away with no cranks if you had two gears...hope she starts and don't run out of gas.
    3. You could use a second jackshaft to go back across to the left side, but that's a lot of gears and chains.
    4. If you had a right hand drive motor in the first place, then jackshafted across to the left... that would probably be easiest.

    Well option number one would be good for me but I'd need to have the thing in hand to say if it's possible. Also my bike frame is aluminum so I'd have to fab the jackshaft mounts myself to weld on. Hmmm, not as excited about my discovery now.
  4. Going with option #3 you could put the 2 speed as jackshaft number 1 and a regular jackshaft as number 2, this way the double chain would be short, just going between the two jackshafts and there would be a single chain going to the rear wheel.
    Another possibility would be to have jackshaft number 2 also be a 2 speed, then you would have 3 speeds total. You'd have a lot of clutches though and it would be pretty pricey at $100 each.
    Brain is free flowing.
  5. Alaskavan

    Alaskavan Guest

    What kind of engine/clutch? If you don't have to bump start, option 3 with a regular jackshaft as number 2 would allow a freewheel on the left and eliminate drag when pedaling. IMO a lot of us get carried away with the idea of having a lot of gear ratios (3,4,5,6,etc.). There are inherent limits to the speed you will get from any particular hp/bike configuration. Better to find something that gives you adequate low end, and acceptable top.
  6. The motor is a Hua Sheng with centrifugal clutch. I got it on Ebay but the kit is also offered at It still hasn't arried yet, I'm just collecting info for future mods.
    Yeah, #3 seems like the most realistic, I just hate the thought of how much noise and drag all those chains would make. I guess I could build some kind of housing to go around it all to contain the noise. Haveing a freewheel on the final jackshaft gear would be sweet to help with pedaling.
    I haven't started learning about chain sizes yet. What is typical motored bike size and how does it compare to #35?
  7. MtnGoat

    MtnGoat Guest


    Bicycle and motorcycle chains left most digit is a 4, referring to the center to center distance between links. 4 means 1/2" pitch (or 4/8's). #35 would be 3/8" pitch. So we are looking for #40 which is 5/16 wide, 41-1/4 wide , and 415- 3/16 wide for motorcycles. 410H-1/8 wide is good when matching to bicycle components.

    The best size is the lightest that is sufficiently strong. You need to match sprocket size to chain size, or visa versa.

    Here's a short primer on chain types:
  8. Douglas65

    Douglas65 Guest

    I would like to take a shot at this if only to get it straight in my head.

    This unit is designed to operate close to 3500 rpm like on a typical B&S or Tecumseh. I believe most engines we would use are closer to 7000. Conveniently double.

    Lets try a frame mount. 10 tooth sprocket (no clutch) on engine crank shaft, going to the first (of 2) or primary jackshaft running a 20 tooth sprocket, that will only be turning half the speed of our 7000rpm engine, or the same speed as this unit was designed for.

    This first shaft will need to be 3/4 inch since it is taking the place of the engine, and the clutch provided is designed to fit on the (3/4inch) crankshaft. The 2 sprocket clutch will fit on this primary shaft.

    Two #35 chains will go a short distance to the secondary 5/8 inch jackshaft which carries the second half of the 2 speed transmission. From this shaft, a freewheeling sprocket will take the power to the back wheel.

    Looks like first gear is 2:1, and second gear is 1:1. The output sprocket can be any chain size you want it to be as long as you can attatch it to the 5/8 inch keyed shaft, and can be on either side of the bike you need it to be on. Cut the shafts as short as you need also. Industrial quality sprockets in many shaft sizes, tooth counts and chain sizes are cheap and easy to come by.

    Any adjustments to the clutches can be done by using different tension springs, removing weight from the clutch shoes or adding weight for more centrifical force applied to the clutch bell.

    With this unit, we have at least 2 places -engine to primary jackshaft, and secondary jackshaft to wheel mounted sprocket- to gear down our engine speed. I haven't done any math, but it seems like this would work. Low gear could be used for take off from start, hills, or any time where up to maybe 15-20 mph is needed. Second would be for cruising at speed, or 20 plus. Get it close on paper, and adjust from there with the real thing.

    Keeping chain noise down would be improved by using short, well aligned chains that are properly lubed.

    The 2 jackshaft unit could be manufactured easily out of aluminum plate and 4 bearings to be bolted or welded into place on many bikes. I only question the longevity of the unit and parts replaceability. How long will it last and can it be fixed? One thing, it is designed (I believe) for up to 6 HP.

    What am I missing? Maybe I should take a stab at the math next.
  9. reclaimer

    reclaimer Guest

    I needed to reroute my chain path. Thinking since I need to add a jack shaft I might as well try one of these. I think I can rig up some kinda electric start.

    I need help with the gearing thou. I have a 48cc Happy time(10t)and my rear wheel(26") has a 44t sprocket. I've got the 2speed parts and a 3/4" jack shaft. I'd like it to go 30mph, if 25mph would greatly reduce clutch wear I'd settle.

    edit: if i were to put a 20t on the primary jack shaft and a 10t on the output to the wheel. Would it be like a 88t 1st gear and a 44t high gear at half its normal speed(because of the 20t halving the engine's rpms) ?
    Last edited by a moderator: Apr 4, 2008
  10. reclaimer

    reclaimer Guest

    After playing with the excel ratio calc that loquin posted, maybe I got it. The ht's 10t to the rear wheel's 44t is 4.40:1, if I put a 20t on the primary shaft and a 20t to the rear wheel the high gear would also be 4.40:1.

    I was thinking of putting in a temporary jack shaft with a 1:1 ratio to break the engine in, and it hit me, duh 20 in 20 out. Anyhow, is this correct?
  11. reclaimer

    reclaimer Guest

    I've been searching the net for info on this set up. I haven't found much yet.

    One short three reply topic on a forum, a guy says the comet clutch's shoes are adjustable to engage at two different rpms.(I'm assuming thats the high gear as the primary clutch is not a comet)

    edit: After reading a longer thread at a mini bike site I don't believe that is true. It talks about the secondary clutch engaging too soon. They were able to get stiffer springs that engage at 3300 rpms. So I figure it engages some where between 2500-3000 rpms. Which would have my H.T. at 5000- 6000rpms.

    Doesn't that seem too high? I'm afraid I wont have enough revs left in high gear. Maybe 2:1 between the engine and primary clutch's jackshaft is too much?

    Then theres this, not a bike but shows how versatile this can be.

    In this project the primary clutch engages at too high an rpm. He modifies it to engage at 1200 rpms. making me think it engages close to the standard 2200 rpm for maxitorque six shoe clutches. Putting my H.T. at 4000-4400 rpms. Again that seems high, but I'm no expert.
    Last edited by a moderator: Apr 6, 2008
  12. If you keep the 12 tooth as the driver and a 12 tooth as the low gear output there will be no change in the ratio... speed will be the same as your stock 10t to 44t with no jackshaft. How big of a jump you will get when it jumps up to the 24t sprocket? Not sure. You will be able to adust that with either the sprocket on the jackshaft or the second sprocket on the wheel.

    You could increase the jackshaft RPM to go faster by useing a less than 12t as the driver and then compensate with larger output sprockets. It gets confusing quickly.
    Last edited by a moderator: Apr 6, 2008
  13. Alaskavan

    Alaskavan Guest

    I'm bidding on one on ebay. It looks interesting.
  14. graucho

    graucho Active Member

    Dudes! how fast do you want to go on a bike? ive dealt with 2 sp jackshafts for 5 years. Im not going to even give any advise on this other than if you put one on your bike, youll die! You better re-weld and modify the frame to go on the salt flats. (im only talking out of luv)
  15. reclaimer

    reclaimer Guest

    Well I certainly don't wanna go that fast, lol. I'd love to not have to peddle if I don't feel like it though. I don't wana go faster than stock, just wana add a low gear. (I would aslo like to not destroy it right off the bat because I have no clue what I'm doing.)

    It might need a half link as the 12t to 24t chain is tight the 12t to 12t is fairly loose. Seems to fit between my seat tube and fender well enough.
    Last edited by a moderator: Apr 6, 2008
  16. graucho

    graucho Active Member

  17. Alaskavan

    Alaskavan Guest

    I'm with you there Reclaimer. I'm looking for some serious hill climbing ability. The top on the bike I'm thinking of using this for only needs to be 20 - 25 mph, and I would rarely be in that neighborhood.


    I'd like to be able to ride up this 1/2 mile hill. Instead of walking along side the bike like I did last time. And there are other hills around that are even steeper.

    This might not be the answer, but I'd like to give it a try .
  18. reclaimer

    reclaimer Guest

    I bought my 2speed kit from bmikarts, they out shipped northern tool by 3 days.
  19. Ghost0

    Ghost0 Guest

    Is this what you guys are looking for? With this system I have comparable gearing to running a 58t rear sprocket all the way down to a 29t using the rear casset. I am now looking into doing one for a 4 stroke frame mount. I haven't looked into a rack mount yet but all in good time.

    Attached Files:

    Last edited by a moderator: Apr 7, 2008
  20. Demosthenese

    Demosthenese Guest

    ghost is there a build page of that thing up somewhere??? that is a VERY slick setup, can't beleive i haven't seen it before. You should sell plans.


    ahh i see, here is a more comprehensive link
    Last edited by a moderator: Apr 7, 2008