Sprocket Alignment

Discussion in 'Frame Mounted Engines' started by CMA_Decky, Nov 3, 2008.

  1. CMA_Decky

    CMA_Decky New Member

    I've run into a problem while assembling my bike. I'm mounting the engine on a mountain bike. However, the way the tire is compared to the frame the sprocket on the engine is about an inch offset to the centerline from the tire sprocket. This appears to be just enough to cause the chain to jump the sprocket into the gap between the sprocket and the spokes. Anyone have any ideas for fairleading the chain? I was thinking mounting a guide raile on the inboard side of the sprocket so that it can't jump to the inside.

    Please help, i've put too much money into this thing to watch it not work.

  2. rustguard

    rustguard New Member

    I'm no expert just a noob in the scheme of mb, but I just had the same problem. The bike I had choosen was an older 700c model with 6sp hub and rear spacing of 125mm, firstly I packed out the engine drive side to 132mm width and redished the wheel. Next I ground out the id slightly of the sprocket to fit right up the hub with about half a mill gap to the spokes, then I thinned out the rubber washer a bit tapering it to the spoke angle, then using a texta I marked out the outside 18 spokes on the rubber and using a very thin cut off disk made some slight grooves a bit deeper than the spokes. After all this it was maybe about 3 or 4 mill off centre. I'd say the best bet would be to post a photo so the more experienced guys can input. If it is already a 135mm wheel may need a different one? Here is a pic the packing is rudimentary and the silver piant splatter is almost criminal but you should see what I mean?
    Edit: oh yeah the sprocket supplied in my kit had no dish, this would have made things easier- but oh well.

    Attached Files:

    Last edited: Nov 4, 2008
  3. HI,

    Hard to tell without good pics BUT I have heard of some folks adjusting the cones on the rear wheel to help get a better chain line alignment.

    Hope this helps.


    PS- Although it is better to have a nearly perfect chain line it doesn't have to be perfect to work (an example would be riding a multispeed bike and having the chain on the inner chain ring up front and the small sprocket on the back....It can be done but obviously not optimal from a wear standpoint....

    Also, have you beveled the teeth on your rear sprocket ?(possibly front too BUT more often than not it is the rear one that needs it)...THIS can make a BIG difference in the chain staying on or not....I'll try to attach a pic to show you what the tooth profile should look like (you can do a rough job of it with a grinder or hand file).

    The pic below is the tooth profile of one of our sprockets...

    Attached Files:

  4. CMA_Decky

    CMA_Decky New Member

    Rustguard, it sounds like you know what you're talking about but unfortunately, I do not. Mind dumbing it down for me (I enjoy pictures, particulary with your modifications to the engine sprocket)? As my lude crude schmetic illustrates the engine sprocket is nearly in line with the edge of the tire so I believe that if I'm moving any sprockets it should be the engine one otherwise I might run into chafing issues with the tire. I was thinking of using a fairlead similar to the one used to shift gears on the front sprocket. I realize that this wouldn't be ideal from a wear stand point but does anyone think that that's a realistic option?

    Also, there appears to be appx. 5 mm of wobble in the tire sprocket which I cannot correct (stripped a bolt head :mad:), is that too much?

    Attached Files:

    Last edited: Nov 4, 2008
  5. rustguard

    rustguard New Member

    hmm, I guess the first advice would be to never over tighten a thread, to loose is better than too tight. so you want to try to loosen one side rather than tighten the other.
    It is very important to have a lead (bevel on the sprocket) otherwise the chain will come off. as andy demonstrated. You cant compare it with a derailleur setup as the chainwheels are specifically designed for that purpose. 25mm for me would be un-workable. But all problems mechanical on these bikes are solvable. I think you need to post more detailed info on what exactly you have, ie engine, wheel size, the width of your rear tyre, where the engine is mounted? that sort of thing. A pic tells a thousand words, or gets a few more answers.
  6. echotraveler

    echotraveler Member

    im liking rustguards strategy......
  7. Shadeslay

    Shadeslay Member

    I've read a few methods, one stated above adjust the axle cones and use washers to space the sprocket. Another would be to use another spacer or thicker spacer on the sprocket. From what I've read 1" isn't to bad, are you certain the sprocket isn't wobbling? I would suggest getting the sprocket as concentric as possible to see if that helps. If not, then move onto one of the a fore mentioned fixes or a combination of the two.
  8. cpuaid

    cpuaid Member

    i also did a mountain bike and had similar alignment problem with the sprockets. if you note where the chain keeps jumping, more than likely it would be the same few teeths of the sprocket. filed down the 44T sprockets as andyinchville1 suggested and so far so good, no chain jumping. alignment is not so critical as chain links seating and releasing in sprocket teeth smoothly.