Rear Sprocket attachment and specifications

Discussion in 'Frame Mounted Engines' started by gilesthealmighty, May 6, 2008.

  1. First things first, this is my first proper post and i'm sorry if this has been said at all before, i have tried searching using terms like "rear sprocket" but to no avail. Please delete/move as necessary :)

    Ok hi there,

    i have two designs for my bike:

    The first one being frame mounted and this is the prefered one.

    ANYWAY, my question is this, beacause i havnt bought a "Kit" i don't have a spare rear sprocket or a gear to go on the end of the motor gearbox. If you look in the pictures i have a 3:1 reducer already but it has no gear.

    WHat i'm looking for is Sprocket A and B and also a chain, ebay isnt being much help so i was wondering if anyone knows a good site to check out for relativly cheap?

    i have done calculations and the small sprocket should be around 12 teeth for the big one to be 56 teeth. So ideally a 12 and 56 tooth gears =)

    oh also preferably UK as that will save postage!

    also would it be worth going to a bike shop? would a mini-moto bike rear gear be ok? humm ..

    FINAL question, how does this gear attach to the rear axel?! i'm really confused as to how all you guys have done it, i can't see an easy way without Welding the gear to the axel! =S

    PS thank you guys this is an awesome forum =)

  2. HoughMade

    HoughMade Guest

    Try here for parts- a UK supplier.

    parts page

    main page

    The way my rear sprocket attaches- and most of them is like this:

    Assuming you have a 36 spoke wheel, it is pretty easy. The sprocket (as you will see from the parts page above), has 9 holes for 9 bolts. Please see the first attached picture.

    There are also 2 circular rubber "washers", one that will be against the sprocket and one that will be inside the spokes. The metal plates shown go inside the spokes. The 9 bolts go through the sprocket from the outside, then the first rubber washer goes on, then the bolts go through the spaces between the spokes, the the next rubber washer, which you will cut a slit in to get it around the axle, goes over the bolts. Finally, the metal plates go on and the nuts. Tighten it down and you are all set. See the last picture.

    The pic is from a supplier over here, dax, he has good directions on his site here:

    Attached Files:

  3. ah wow thats an AWESOME website i can't beleive i didnt find it! Ok thanks thats perfectly answered my question =)

    ah hah i see how its attached, thats rather a neat idea! i'm assuming the little wedge/packer plates are to move it slightly away from the spokes so the chain does not catch!

    Awesome thank you =)

    When its all done i'll put some pics in the 'pictures' topic thingy =) am really getting into this now =P
  4. HoughMade

    HoughMade Guest

    Both to space it and that is what clamps the spokes- you want to center the bolts between the spokes so that the rubber clamps against the spokes and the bolts do not touch the spokes at all. If you tighten it sufficiently and keep it tightened, the sprocket will not rotate on the wheel and the bolts will never touch the spokes. If the bolts contact the spokes, it puts too much pressure on them.
  5. slaptacular

    slaptacular New Member

    THANK YOU for providing this! I can't wait to try this in the morning. The instructions on Bikeberry aren't detailed enough and the pic in the manual doesn't have a good angle. I thought both rubber washers went on the same side of the spokes. No wonder I was having trouble with chain alignment! By the way - my kit comes with 5 metal plates (2 half moons and 3 third moons) for "dual locking". Any suggestions on how to install all 5 of these plates? I was thinking I should put the two half moons on first then the 3 sections on top?
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    They key to your engine installation will be which direction your engine shaft turns, and also the output shaft size and shape.

    Is the shaft 1/2", 5/8" smooth-type, or 6-pinion star-shaped?

    Two-stroke engines turn counterclockwise; with your gearbox installed, engine might turn clockwise. That means your clutch and drive sprocket should face the same side as your bike's chainring and sprockets. You would need a jackshaft to divert the engine drive back to the left side of the bike. Then you'll have to google-research to find appropriate sprockets to create approximately 18.75:1 final gearing.

    A simpler, more effective way might be to utilize SBP kit components and drive your engine through your bike's rear 7-8/speed cassette. The only modification you'd need to do is to drill the SBP motor mounting plate to accept your engine. The helpful crew at SBP can assist you in determining which chainring gear and gearbox sprocket to use.

    FWIW, I'd go the SBP route if I were me. Quality components and the thrill of shifting gears!:jester: