3-speed Jackshaft Build Chain Tensioner

Discussion in 'Photos & Bicycle Builds' started by KCvale, Jun 6, 2010.

  1. KCvale

    KCvale Motorized Bicycle Vendor

    I set out to build my first SickBikeParts Jackshaft shifter kit bike on a nice new Giant Suede 3-speed coaster.

    It is a heavy duty beach cruiser with front and seat shocks, but a low top bar clearance to bar and the pedal crank is forward of the seat post.

    I ordered the 2010 model in the top pic but the only thing they had that was black was the 2009 in the lower pic.


    I love the bike and it looked like everything would fit.

    I got the JackShaft kit assembled fine too.


    Yes, I painted the mounts to match the shiny new Grubee black 66cc GT5 motor with 11 coats of engine paint ;-}

    But when I went to install it with the crank so far forward and as low as I have to mount the motor the chain hits the motor!


    As mentioned I can't go up, there is no room.


    I love the motor where it is, and though I could move it up if I mounted the carb off to the side, that just didn't make any sense to me.

    Now I hate putting any tensioner/idler pulley on a main chain drive, but I don't have a choice here so I looked at my options.

    I figured I would just see if I could use the otherwise stock kit tensioner pully and I can, but there is a small window I can place it in so it doesn't hit the motor or the now to be main drive pedal chain!


    I pondered this problem for two days thinking of how I could add something to the motor to support a pulley and all looked bad until it dawned on me :idea:

    All I need is a modified right side JackShaft mounting plate like this.


    It would look like this from the left where it mounts to the back of the clutch housing.


    And from the right side it looks normal and the pulley can move the length of of the bottom of the motor without touching it.


    I think with this setup you could even use a crank mounted forward AND above of the final JackShaft motor drive sprocket.

    I e-mailed Jim at SickBikes this morning to see if they could offer this plate design as an option with their kits.

    What the heck right?
    It is just a couple more cuts on a little bigger piece of steel, you can use the otherwise unused kit tensioner pulley, and with the 3 point mount to the motor it sure as heck won't flop around like the stock mount can on a chain rail.

    What do you think?

    [​IMG] [​IMG] KC's Kruisers.

  2. Fabian

    Fabian Well-Known Member

  3. Fabian

    Fabian Well-Known Member

    Just thought of another concept.
    You could drill into the end of the jackshaft and insert a roller bearing, then place a pin inside the I.D. of the roller bearing and use the pin to hang a dual (spring loaded) idler roller system.
    This would have the advantage of being self aligning and not needing to modify the jackshaft plates.

    I'll try and draw up an image of the concept.


    Attached Files:

    Last edited: Jun 6, 2010
  4. professor

    professor Active Member

    I think you did real good Kc!
    I love seeing the creative side come out in solving these problems.
  5. KCvale

    KCvale Motorized Bicycle Vendor

    Thanks ;-}

    I heard back from Jim at Sick Bikes, he suggested this:

    "In theory I could make you one but to be honest I just don't have time. All you wonderful customers are keeping me and my partner all asses and elbows.

    I think you can get away maybe just moving the sprocket to the right. I run mine outside of true alignment anyway to increase the clearance between the two chains. Give it a try."

    So I gave it a try.



    There is enough room on the shaft no problem and it just clears the clutch plate, but it looks like it will rub on the clear plastic chainring cover.

    If so I imagine just a washer or two between the chain guard and sprocket will solve that.
    The trick will be to see if the chain wants to jump or wear the sprocket too much.

    Only one way to find out, finish building it and try it out.
    I sure hope it works, it's killing me bringing it this close and not finishing ;-}

    About the link bike with tensioner
    I don't see any reason a right mount for that dual sprocket like a derailer coult not be made as well.

    Certainly a lot less parts and work.
    Cheap too if you have a standard derailer shifter laying around too.

    If I had a metal shop I would have made my design, still might, it will sure be easier to adjust the chain tension without having to move the motor up.

    Actually, if the plate went down on the topic link page you could use the stock pulley and tighten a straight down chain in a jiffy too.

    If I had a bike like that, I could whip up a poster board model for that in no time.
    A single flat piece of metal is pretty cheap to make, and you get the tensioner in the bike kit.

    [​IMG] [​IMG] KC's Kruisers Glendale Arizona, USA
  6. Shiftkit tensioner

    this is what I came up with. Fits on bottom u-bolt of shift kit

    Attached Files:

  7. Fabian

    Fabian Well-Known Member

    Hi gasbikeproject

    I like your variation on the theme of using the U-bolt as a pickup point for the chain tensioner. In my opinion it's the only practical method that doesn't involve modifying the shift kit plates.

    There seems to be a need for a decent chain tensioner for the SickBikeParts shift kit.
    We should start a sticky thread for the things, to get everyone's solution in the same place on the site.

  8. Ghost0

    Ghost0 Guest

    Well in my opinion, and I think I deserve to have one since I designed the thing, if you need a tensioner then you are masking a problem that you shouldn't have. I have never needed one and most other customers have not needed one either. I will admit it is a bit of a balancing act getting the engine at the correct height and the chain length correct. Every bike will have a sweet spot where the engine just likes to sit and if you can achieve the correct chain length in that position you should not need a tensioner. KC's issue is a bit different as he is using a bike that is a bit different with his bottom bracket far in front of the seat tube. Now don't get me wrong I am not saying don't do it or that for odd applications it may be warranted but for most applications it is not necessary.
  9. Fabian

    Fabian Well-Known Member

    I agree with your assessment Ghost on any misalignment issues or bad installation masking problems, requiring a need for a tensioner.

    I'm coming from a different viewpoint though: the point being convenience: set the engine in the frame and never have to bother with readjusting chain tension, as the tensioner keeps compensating for chain wear.
    As a side consequence of installing the tensioner, a source of vibration coming from the chain was reduced.

    As you said, and i do agree; a chain tensioner is not needed, but it makes things somewhat more convenient.

  10. Ghost0

    Ghost0 Guest

    One other thing to be mindful of when installing a tensioner is that it should not be a spring loaded tensioner. If it is and your chain still has too much slack when you try and start the engine it will tighten the tensioner side of the chain causes the backside to go slack which may cause chain derailment during the starting process. Just something to be mindful of.
  11. KCvale

    KCvale Motorized Bicycle Vendor

    ... by moving the motor to adjust chain.

    As Jim mentioned there is always a sweet spot for mounting a motor, and sometimes this leaves little if any wiggle room, especially if you have to drill the bike for the front mount.

    Granted we are not talking too much movement, and not very often, but even for install sometimes even a 1/2 link won't let you get it perfect without moving your mount point.

    An optional right mounting plate that goes down vertically from the back side of the bearing mount to the front a little less than my design, and down about 3-4" with a vertical slit for the bike kit tensioner pully would be a really handy option.

    It wouldn't solve my unique problem of a forward crank AND low cross bar, but it might very handy for many others.
    One thing is for sure, just loosening on nut and moving the pulley is a whole lot faster and easier than moving the whole motor.

    Now back to my build...

    I got it all done using lock tight, motor mounted, the works, and went to try it out and the motor has a bad clutch!!!

    Everything is together right, there is the usual resistance on the clutch plate arm, etc. But even by actuating the all the way with a tool won't release the clutch.

    I'll mess with that later, I have a brand new black Grubee Skyhawk 48cc here and already started fitting the kit to it.

    On the bright side I am certainly learning the darn thing taking it on and off so many times ;-}
  12. Fabian

    Fabian Well-Known Member

    Have to agree with your locic Ghost: it will tighten the tensioner side of the chain causes the backside to go slack


    that's axactly what happens to my drive chain when pedal starting using my chain tensioner set on the delivery circuit of chain travel.
    So far in 6,000+ kilometers of riding, the chain has not suffered disengagement issues when pedal starting, even when quite loose, but there "will" always be the first time.
    For this reason, my prefered chain tensioning system would be as per my illustration, to capture and tension both the receiver and delivery circuit of chain travel; doesn't matter which side of the circuit is slack, the tensioner will operate with equal efficiency; also being self aligning and compact.

    Last edited: Jun 9, 2010
  13. KCvale

    KCvale Motorized Bicycle Vendor

    Don't you hate it when life throws you a curve ball at the worst time?
    My mom is in the hospital and though she will make it she will never be the same person.
    My time for messing with the shift kit build may end up being longer than I had hoped.
  14. KCvale

    KCvale Motorized Bicycle Vendor

    Here it is 10 days later, great weather outside, and I set out to get this 48cc on with the shift kit once again, DISASTER!

    I really screwed the pooch this time, I damaged the actual Jackshaft shaft.



    The shaft needs to move freely back and forth between both bearings, both gears, and the right side shaft stay.

    The ends are toast and so is the shaft.
    I trashed it trying to solve the 66's bad clutch problem.

    I am going to name this bike Elinore.
    After the elusive Mustang in the Nicolas Cage movie.

    [​IMG] [​IMG] KC's Kruisers Glendale Arizona, USA
  15. KCvale

    KCvale Motorized Bicycle Vendor




    I look like a giant on it, but note my left foot is fully extended and I am 6'2 and 165 Lbs.

    She turned out pretty good though, and a real pleasure to ride.


    I finished mounting everything like the lights and computer/speedometer and did all the detail work, it takes awhile.
    Despite 4 cables and 2 wires going to the handlebars I managed to size and zip-tie them in nice and neat.


    I love how clean my Keylock Ignition Modules go on, it really cleans up the look. The black thicker real gas line helps too.


    The bungie cord came with the bike and I used a 6-pack Igloo for storage in that pic for multiple reasons but I am making something else now.

    Now I just need to get some video of it in action.
    I am thinking a small hot babe and shooting the video from the back of a pickup pacing just ahead of the bike.
    Something good for YouTube.

    The sound of the shifting and acceleration are pretty cool, I love it ;-}

    [​IMG] [​IMG] KC's Kruisers Glendale Arizona, USA
  16. KCvale

    KCvale Motorized Bicycle Vendor

    Thanks for the tips guys but I didn't need a tensioner anywhere after all.

    I think she turned out pretty well. I have put some miles on her now and I tell ya what, despite all the obstacles I had to face building it, she was was worth it.

    I am taking it easy and still on my first tank of break-in mix but can ride 30 MPH half throttle in 3rd in traffic in 111F heat and no problems at all in real comfort.
    Well, as comfortable as you can be out in the sun when it's over 110F.

    The ride and shifting are so smooth I really have to pay attention to my speed, when I'm on the road that is, riding the paved canal bank bike trails are another story ;-}
  17. locoWelder

    locoWelder Guest

    sweet ride KC! I to lived in the valley of the sun dont miss the heat dry or not!
  18. KCvale

    KCvale Motorized Bicycle Vendor

    Thanks loco, and ya, this next 3 months kind of sucks heat wise, but come winter I don't have to shovel sunshine.

    With the DUI laws and enforcement here, a little shop and some promo and I think I could get quite comfortable putting out quality bikes as a living here.
  19. KCvale

    KCvale Motorized Bicycle Vendor

  20. ibdennyak

    ibdennyak Guest

    Nice bike, but....uh.....what happened to the *small hot babe*? Been waiting for that. :grin5: