Building double suspension Mt.

Discussion in 'Frame Mounted Engines' started by fairracing31, Jul 22, 2007.

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  1. fairracing31

    fairracing31 Guest

    Anybody else trying to build a double suspension Mt. bike? I'm having great trouble keeping the chain on when suspension is fully compressed. I have tryed using a spring tensioner among other's but the spring tensioner seems to work the best. It works great on the road, but off-road, any good size bumps or jumps the chain wont stay on. Anybody have any ideals?

  2. srdavo

    srdavo Active Member

    pics, man....we need pics!!!! :D
  3. fairracing31

    fairracing31 Guest

    Sorry, dont have a camera yet. Hopefully soon.
  4. iRide Customs

    iRide Customs Member

    I agree! Let's see your project.
  5. thatsdax

    thatsdax Guest

    You will need

    you will need chain guides at the top and the bottom of the rear sprocket just like a dirt bike. Check one of them out and copy it. no sense in re inventing the wheel. Enjoy the ride..
  6. I have thought about doing this also but there are challenges.
    So everyone knows that as the suspension moves through it's arc it affects the chain so there needs to be a way to minimize that.

    one way (ideally) would be to have the swingarm pivot in line with the drive sprocket shaft (maybe even a custom jackshaft setup).This would work best but would be difficult to do.
    So the next best thing to do is get the drive sprocket as close to the swingarm pivot as possible to minimize the affect of suspension movement on the chain.

    Or a very simple way would be to mount the engine over the back wheel.

    There is one other way that I think would work and the credit goes to mickal1025 for his custom pivoting engine mount that looks like it could be modded to work on a fully suspended bike in various ways.
  7. srdavo

    srdavo Active Member

    would that need to be centered with normal rider weight on it? (to allow for both up & down motion on the swingarm?)
  8. fairracing31

    fairracing31 Guest

    Well I am using the set up on a 1982 YZ 125. I have used guides and rollers, The guide is on the bottom and roller on top. Thats all a dirt bike uses, but it's not working. The best thing that has worked is a home made spring tensioner. But the tension that I need to keep the chain on when the shock is compressed, ends up way to tight when there is no compression. I'm using a shock with 4" of travel, it might be to much. I realy would like the 4", but I think in the next few days I will try to use a smaller shock, I might have to re-do my swingarm that I made to fit a smaller shock.

    Whoaa, just had a Ideal. Is there anyway to convert my chain to a belt? I can make a belt stay on better then a chain.
  9. I would think to set it to the middle of the suspension arc so that at either end of the suspension arc the chain would be within useable range.
    While rider weight is a factor I feel the overall suspension travel limits and the chain tension at those points would be the more important thing to look at.

    Ok so with the chain set with proper tension when the drive sprocket shaft, swingarm pivot bolt and rear wheel axle all are in line.
    As the suspension moves either up or down the chain would slack up since the distance between the drive sprocket shaft and the rear wheel axle move slightly closer.
    The closer the drive sprocket is to the swingarm pivot the better since it effects the chain staying tensioned properly.

    I guess with the proper chain guides up near the engine it could help take up the slack.
  10. mbatl

    mbatl Guest

    where did you mount the engine? under the frame just behind the front wheel?
  11. Ghost0

    Ghost0 Guest

    You could use a jackshaft kit which would transfer the engine drive to the chainring so the bike wouldn't know it had an engine on it and the suspension and chain would work normally. That is one of the reasons I designed the system anyway. In addition you would also have the ability to shift which makes offroad riding much more enjoyable.