Chain Tensioner tension wheel modification for 50cc frame mounted motor

Discussion in 'Transmission / Drivetrain' started by sakeynes, Apr 22, 2009.


What do you think?

  1. Don't have any problems with supplied bracket

  2. I've got/used a better idea

  3. I might just give it a go

  4. Looks ****, and what is it with this stupid poll?

  1. sakeynes

    sakeynes New Member

    I thought I would share my modification of the tension wheel with the community.

    I was unhappy with the tension wheel bracket supplied with my zbox 50cc engine kit. My chain had quite a lot of slack in it and this seemed to increase the force applied to the tension wheel bracket when I started and stopped. The result was it kept moving out of alignment and dropping the chain between the spokes and rear sprocket - not a good thing as the rear wheel locks!

    I fixed it with a new bracket, as pictured, that was secured top and bottom.

    The bracket is flat bar aluminium, cost me about A$8.
    At the top it secures to the same thread as the rear rack.
    At the bottom I had to make the same shape as the existing bracket. Easiest way to do this was get a block of wood, drill a large diameter hole in it, then cut the wood in half, through the hole, to make a stamp. Then place the flat bar and a bit of solid bar (I used a handle from my socket set) in your stamp and hammer the **** out of it to forge the curved shape.
    The slot to adjust the pulley height was made with a round file.
    The aluminium is soft, so when I first tightened the nut on the tension wheel, the flat sides of it's shank just gouged through the aluminium. To fix that, I removed the bolt, and with a grinder made two flat sides on the round head, so that I could hold it with a spanner on its end. Then I was able to tighten it up.
    I also had to twist and bend the bar slightly to have the wheel running in the same plane as the rear sprocket.

    Now I ride and free roll without crapping my myself with the thought of the chain dropping into the gap again and seizing up the rear wheel! And it's fractionally lighter as well!

    Attached Files:

    Last edited: Apr 22, 2009

  2. machiasmort

    machiasmort Active Member

    Good idea,

    Some of the other guy's came up with some good ones also, run a search!

    What kind of Diamond Back frame is that? Looks a little like the one I have... It's a Killer bike!
  3. sakeynes

    sakeynes New Member

    It's a Topanga frame. It'll still be around long after humans have left the earth...
  4. rustguard

    rustguard New Member

    imo chain tensioner is not necessary on bikes with horizontal dropouts and derailleur gears. Every curve you have to drive the chain around will cause energy loss and bleed effort. if you do feel the need to use one then get the chain as short as possible then take up the remaining slack, that way you minimize the energy loss
  5. sakeynes

    sakeynes New Member

    Thanks rustguard,

    But I removed as many links as possible and still needed the tensioner. The fact that the chain becomes tensioned at the top during motoring and tensioned at the bottom during starting means that a tight chain is important, for stability on the rear sprocket and to minimise dynamic loads. I've just shown one alternate way to achieve this compared to the factory supplied solution, and that was really the point of the post.

    Obviously every bend takes energy out of the chain. With a bit more run in and chain stretch I bet I'll be able to take a couple more links out, and straighten the chain run a little.
  6. machiasmort

    machiasmort Active Member

    Mine is a diamond back "curaca". Is yours older? That's a well put together frame.
  7. lordoflightaz

    lordoflightaz Member

    My neighbor designed this one. First 2 pics are on his Jaguar. Last is on my Skyliner, I don't have it on now as the stock one works for me, with just a slight twist in it. I may use the spring one if I go to a smaller sprocket.

    Note: I said he designed it. I messed with it a bunch and depending on how you put it together you can mount it higher or lower as well as closer or farther from the frame without much trouble.. You can buy it at livefast.

    Attached Files:

  8. cpuaid

    cpuaid Member

    very nicely done. it looks very easy to make so i think i'll give it a go for my bike. i also like the one made from an inline skate wheel but have nothing available that can cut a nice groove in the wheel.
  9. fm2200

    fm2200 Member

    Most of the pics I've seen the adjuster is being used to the extreme and the chains are looking very taunt. I know that a more passive use of the adjuster insures less friction for the chain and less drag. When taking the slack out of the chain remove links first, then use the adjuster to remove the rest of the slack. Too many if you are only using the adjuster and that simply is not the best solution. The least amount of deflection is best for both the chain and the alignment.
  10. lordoflightaz

    lordoflightaz Member

    If you are good at cutting and bending 1/4'" steel, no probleml, buying is probably easier.
  11. rustguard

    rustguard New Member