Idle Pulley Torques Inward

Discussion in 'Motorized Bicycle Trouble Shooting' started by VTHokie, Dec 29, 2012.

  1. VTHokie

    VTHokie New Member

    Joined:
    Dec 18, 2012
    Messages:
    42
    Likes Received:
    0
    Hey again,
    My new idle pulley (after they forgot one in the original kit) torques inward toward the wheel, no matter how tight I bolt it upright. The frame isn't truly round at that point, and is slightly oblong, which is contributing to this inward torque of the idle pulley bracket and bearing - which means, the chain gets pulled off after a short pedaling.
    Any suggestions to prevent this torque?
    Originally (because it was missing from my kit), I was going to not use an idle pulley, but I can't get both chains tight, no matter how many adjustments I do to either chain with chain breakers, master links, etc. So, I'm gonna get this dang idle pulley on there hopefully and be done with it.
    I was thinking of wrapping electrical tape on that portion of the frame to shape it more roundly.
    --OR--
    I could dremel the spot out a bit to make it round, but I'm afraid of weakening the frame
    Let me know what you guys think
     
  2. ocho ninja

    ocho ninja New Member

    Joined:
    Jan 14, 2012
    Messages:
    565
    Likes Received:
    0
    You could drill a hole trough the bracket for the pulley and thread a set screw for it

    Or a even stronger solution would be to tack weld it to your frame, if it's steel of course.
     
  3. GearNut

    GearNut New Member

    Joined:
    Aug 19, 2009
    Messages:
    5,106
    Likes Received:
    0
    #3 GearNut, Dec 29, 2012
    Last edited: Dec 29, 2012
  4. maniac57

    maniac57 Old, Fat, and still faster than you

    Joined:
    Oct 8, 2011
    Messages:
    4,493
    Likes Received:
    1
    You can get it tack-welded at most muffler shops. The thread above has many ideas, but I like welding for maximum security. I've never lost a rim yet.
     
  5. crassius

    crassius Active Member

    Joined:
    Sep 30, 2012
    Messages:
    3,147
    Likes Received:
    2
    Sounds like you're trying to bolt it where you want it rather than using the oblong shape to bolt it solidly. Tightening it on that oblong helps to hold it in place (assuming your bolts aren't stretching, in which case I like 12.9 replacements).

    Once it is tight, you can decide whether to add a washer or two to the roller to put it where you need, or take it back off to bend the upper part a bit so when put back on it will be in the right place (don't bend it on the bike).

    In a case in which the frame isn't thick enough to hold it, and inch or so of handlebar, split into a 'c' shape can be put under the clamp to give it more bite.
     
  6. GearNut

    GearNut New Member

    Joined:
    Aug 19, 2009
    Messages:
    5,106
    Likes Received:
    0
    Another issue with these stock tensioners is the mount bracket, without any modification, holds the tensioner wheel true to the angle of the chain stay tube. The tube is at an angle in relation to the chain run. This means that the chain will run crooked in the tensioner wheel. You will need to twist the mount bracket a little at a time until the chain runs straight through the tensioner wheel. Do NOT try to twist the mount bracket while it is attached to the bicycle chain stay tube .Remove the tensioner bracket from the bike and clamp it in a bench vice (assuming you have a bench vice) and then twist it. If you have 2 large crescent wrenches you can use them to twist the bracket if you have no bench vice handy. Hold the bracket tightly in 1 wrench and use the other wrench to do the twisting. Be careful as the 2 wrench technique can slip and "bite" you.

    If you make a tensioner strap that goes from the top seat stay tube to the bottom chain stay tube, like the ones in the link I suggested, this avoids all of this twisting and chain angle aligning stuff.
     
  7. crassius

    crassius Active Member

    Joined:
    Sep 30, 2012
    Messages:
    3,147
    Likes Received:
    2
    Occurred to me last night that the problem may not be in the tensioner at all. The few times that I have seen that much force applied by the chain to the tensioner have been when the rear sprocket wasn't quite centered in the up/down direction. This makes the chain run loose at one point & tight at another. Sometimes one can live with this by being sure that the chain is at its tightest spot when setting the tensioner (leaving it much looser at the loose spot). This will get rid of the larger forces pushing on the tensioner, but the better fix is to redo the sprocket mount to center it better.
     
  8. VTHokie

    VTHokie New Member

    Joined:
    Dec 18, 2012
    Messages:
    42
    Likes Received:
    0
    Thanks for the responses,
    It occurred to me to bend the bracket in a vice as mentioned above, but I was too unsure of the exact angle to try it, but I might now. Either that, welding, or tapping the frame sound like great ideas. I will talk it over with my buddy and come up with a conclusion, and hopefully have some good news to report tomorrow.
    The rear sprocket is centered, to the best of my knowledge, but the rear wheel definitely needs to be balanced a little better - a work in progress.
    This is the second tensioner bracket I've installed, and both torqued inward, which led me to the conclusion that the shape wouldn't allow it. I'm gonna take good long look at everything involved with it again tomorrow and we'll see how it goes.
    Thanks again
     
  9. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,287
    Likes Received:
    1
    VTHokie,
    Did you take a look at the link that GearNut provided? http://motorbicycling.com/showthread.php?t=11815&highlight=tensioner

    There are some very good suggestions and a lot of discussion regarding the tensioner in that old thread. If it doesn't help you might try typing in 'chain tensioner' in the Google Custom Search and you'll have pages to read on the subject.
    Good luck and let us know what you come up with.

    Tom
     
  10. Ron344

    Ron344 Member

    Joined:
    Oct 13, 2012
    Messages:
    191
    Likes Received:
    0
    I had a problem with mine because the frame was to small so I put each side of the tensioner in the vice and compressed it together some to make it tight, then reinstalled. I did have the bend it to right angle of the frame to align the roller. I later replaced it with a homemade tensioner.
     
  11. crassius

    crassius Active Member

    Joined:
    Sep 30, 2012
    Messages:
    3,147
    Likes Received:
    2
    Another thing that can put excessive force on the tensioner is of the tensioner isn't aligned to feed the chain straight up onto the bottom of the rear sprocket, the chain can miss the teeth and wind around the outside of the sprocket (which makes it WAY too short).
     
  12. maniac57

    maniac57 Old, Fat, and still faster than you

    Joined:
    Oct 8, 2011
    Messages:
    4,493
    Likes Received:
    1
    The tensioner takes the most abuse when starting a new, tight engine. Do whatever it takes to secure it before you get hurt. Twisting to line up the idler wheel better and tack-welding the tensioner should cure your problems. If you decide to weld it, be sure it is positioned to give you the most range of adjustment in the chain BEFORE you weld it.
     
  13. VTHokie

    VTHokie New Member

    Joined:
    Dec 18, 2012
    Messages:
    42
    Likes Received:
    0
    I ended up adding a tensioner that is bolted to both bars, and it feels extremely sturdy. I got the idea from the thread provided earlier
    I gave it a test ride today and it held up superbly, but due to my inexperience in balancing the rear wheel, I blew apart my coaster brake and lost all the bearings. BUT, the tensioner held up perfectly, and I'm extremely happy with it.
    Thanks for all the advice and suggestions.
    Here are some pics:
    [​IMG]
    [​IMG]
     
  14. GearNut

    GearNut New Member

    Joined:
    Aug 19, 2009
    Messages:
    5,106
    Likes Received:
    0
    Good job with that tensioner!
    I am sorry to hear that your hub blew apart.
    May you have better luck with the new one!
     
  15. VTHokie

    VTHokie New Member

    Joined:
    Dec 18, 2012
    Messages:
    42
    Likes Received:
    0
    Thanks for the examples, GearNut. Those cushion clamps are priceless - I bought a variety in case I need them for future work.
     
  16. crassius

    crassius Active Member

    Joined:
    Sep 30, 2012
    Messages:
    3,147
    Likes Received:
    2
    thought it might be a rear sprocket problem causing all that force

    new tensioner looks good & solid, but I'd guess the old one would work when your sprocket gets fixed
     
  17. VTHokie

    VTHokie New Member

    Joined:
    Dec 18, 2012
    Messages:
    42
    Likes Received:
    0
    Ahhh that's an interesting point, and it makes complete sense. I'd be lying if I said I didn't notice a significant wheel wobble, but I selfishly wanted to get the bike up and running before I worried about it -- lesson learned. I'm sure you're absolutely right, and the wobble torqued the tension bar out of place every time. I should've gotten that dang wheel balanced to begin with. After watching a video on tightening / loosening the spokes, I realized that adding that rear sprocket probably threw everything out of alignment (because the bike itself was brand new and would be in no need of truing under normal conditions). Hopefully I can find a place to put it back together today
     

Share This Page