Jackshaft Non-jackshaft shifter kit for HT... Ideas...

Discussion in 'Transmission / Drivetrain' started by heathyoung, Dec 15, 2008.

  1. heathyoung

    heathyoung Member

    Now I know that there is the excellent sickbikeparts shifter kit around, but due to the absolutely abysmmal exchange rate between AUS$ and USA$ its twice the price :(.

    So... I was rummaging around my parts draw and found a 53/39 road bike chainring + a front derailer. When the chainring is flipped backwards (ie. biggest ring to spokes) the ramps and pins are going the right way around for the CCW rotation of the chain. Hmmm...

    When the front derailer is mounted upside down on an adaptor attached to the dropout, its range of movement is goood enough to transfer the chain from ring to ring. Due to the complication of both the top of the chain (when motor driven) and the bottom of the chain (freewheeling) in tension, two chain tensioners would probably be needed.

    The motor sprocket is the correct pitch, but too wide, machining it thinner would allow a normal MTB chain to be utilised.

    This gives a range of 1:5.3 to 1:3.9 for good hillclimbing ability (rather than outright speed) although there are 48/38/28 chainrings readily available as well. The dropout spacing may be too narrow for 3 chainrings though.

    Thoughts? Biggest problem will be the chain tension I think.

  2. Hmmmm....I like the idea of reusing readily available parts and the front derailleur idea is good as well....I am wondering tho How would the 2 or 3 chain rings be mounted to the rear axle?.....I suppose A possibility would be to use a Top Hat Sprocket adapter BUT then the sprockets would have to have an adapter to fit onto the Top Hat itself....

    The other issue would be having to make a spring loaded tensioner that would "follow" the chain when it moves from one sprocket to the other....I suppose one could weld up a tensioner arm to the cage of the front Derailleur so it "tracks" the movement of the chain?....Or perhaps 2 derailleurs could be used in tandem off 1 cable...One does the actual "shifting"....while the other merely moves in sync with the other to keep the spring loaded tensioner in line with the chain....

    Only other problem I can maybe see is when one "bump starts" the engine...If the tensioner is on the bottom won't that cuse a lot of stress on that tensioner (I think?)....
    I almost have to play with a working model because it is hard for me to visualize.....I think it could work BUT the tensioner has to be pretty beefy to compression start the engine.

    Go for it!....I like the idea / concept!

    Happy Holidays!

  3. Skyliner70cc

    Skyliner70cc Active Member

    I have the original left, right, and center "plates" that came on the 1st generation SBP shifter kit. You can have it for whatever shipping would cost to your location. You'd still need to purchase a freewheel crank and a 5/8 jackshaft with gears. I upgraded my shifter kit to the thicker and reinforced plates. The plates are a little bent but can easily be straightened out and put to use.
    Let me know.

  4. heathyoung,

    Unfortnately Andy is right!

    The slack side of the chain while running, (the bottom), needs to be relatively taught in order to start the engine, and free there-after. A separate chain tensioner would make a deraileur inoperable.

    To make it work:

    You would need to make a heavy duty deraileur with a spring loaded locking pin that was connected to a cable and lever on the handle bars, or rely on pull-start.

    Lock the deraileur to start the engine and release to shift gears.

    Good thinking though...The first time I rode an engine powered bike I thought of the same thing, (this thing needs gears),...and then I realized it was going to be to fussy to make it work right. The SBP jackshaft kit is your best bet.

    Last edited: Dec 21, 2008
  5. Skyliner70cc

    Skyliner70cc Active Member

    Yep, SBP kit is a great bet. Don't know how old or young heathyoung is but if he is a youngster, perhaps he has an annoying sibling he can sell into slavery to cover the cost of a SBP kit?
  6. heathyoung

    heathyoung Member

    I was thinking that the problem would be with the chain tension - it needs some slack for the derailer to work, but when you start the engine, you need a lot of tension (especially with the high compression motor I'm building - no head gasket, removed the 'lip', and honed the head and jug with 1200 grit, ported rather heavily as well).

    The engine could be bump started with the chain on the largest cog (highest chain tension) but on the smaller one - no dice.

    I am a big fan of the idea of the SBP setup, but the exchange rate and family pressures have made it a no go, economically speaking.

    The front derailer differs from a rear in that it isn't sprung - hence it doesn't need to be locked (it acts on the sides of the chain). Its probably still an interesting christmas project...
  7. machiasmort

    machiasmort Active Member

    Yep, SBP kit is a great bet. Don't know how old or young heathyoung is but if he is a youngster, perhaps he has an annoying sibling he can sell into slavery to cover the cost of a SBP kit?

    Skyliner70 - see our World economy thread!

    Good idea tho guy's!
    Last edited: Dec 22, 2008
  8. machiasmort

    machiasmort Active Member

    Wondering how you ever made out?
  9. heathyoung

    heathyoung Member

    Had problems with the chain wandering too much (could never get the tension right unfortunatly)