Fabricating a large rear pulley

Discussion in 'Rack Mounted Engines' started by Nashville Geoff, Oct 16, 2008.

  1. Nashville Geoff

    Nashville Geoff New Member

    I'm trying to either purchase or fabricate a large pulley that can be attached to a 26" rear wheel. I'm not using any gear reducing box- Just a centrifugal pulley clutch on a rear-mounted Lawn Boy two-stroke. I had seen a motorized bike, I believe from India, that was using what I thought was a smaller wheel rim as a pulley... That's appealing, but I wonder how well a V-belt would grab without a proper channel, or if it would get twisted, etc. I'm also wondering if anyone has "done the math" as to what size pulley, or wheel, might be the best choice. I want to let the engine operate within it's torque band. I think that with some very well engineered mounts that this could be a very quick & dependable motorized bicycle. Comments, suggestions, part resources? Thanks, Nashville Geoff

  2. bigkat650

    bigkat650 Member

    research GEBE here... similar to what you are talking about, and can figure out the correct ratio's for your gearing/belt length
  3. lowracer

    lowracer Member

    rim pulley

    I had a motored bike years ago that I spot welded an rim hoop of the same size to the rear wheel. Had to bend the frame slightly for clearance. The front pulley size can be changed cheaply to affect gearing. It can be tensioned to minimize slipping. Can even add a brake lever operated tensioner. Some folks have added 'gription' to the rim pulley (skateboard grip tape, rubber cement glue, spray v-belt dressing etc.) I personally didn't use 'gription' & ran mine with no clutch (direct drive) utilizing engine braking...
  4. Nashville Geoff

    Nashville Geoff New Member

    Alex, I hadn't thought of welding two rims together... I like that idea; it would strengthen the driven rim. I'm thinking of running a centrifugal v-belt clutch. Any ideas about a v-belt gripping & tracking well on a rim? I suppose that grip shouldn't be much of an issue, with all of that contact area- But making it stay straight might take some engineering.

    Nashville Geoff
  5. lowracer

    lowracer Member

    I tried the centrifugal v-belt clutch without much success. It didn't function as good as I thought it should. The engine I'm receiving soon in the mail has a built in 78mm clutch. I just need to attach the clutch drum w/shaft to mount the fixed pulley on. The rear rim pulley works well & without any problems of the belt wanting to ride up the rim as long as you get the belt line fairly straight with the driving pulley. By not driving the spokes, the wheel is much more durable. Many people I read about break spokes w/the sheaves that attach to the spokes. The belts are very cheap & available in most lengths at any auto parts store. I never had to replace the one I used for that direct drive application.
  6. Happy Valley

    Happy Valley Active Member

    I'm interested in this conversation.

    Attaching a same-size rim to the wheel pretty much eliminates any rim brakes on the rear, no? Also, wouldn't attaching a second 26" rim to the existing 26" rim result in very low gearing? I seem to recall the gebe sheave being somewhere around 17-18".

    I've got a brand new Robin 35 sitting in a box just waiting for a drive set-up and I'm thinking hard about a flat, toothed belt driven rig.
  7. lowracer

    lowracer Member

    Rim pulley

    The rim welded on pulley does require the use of either a disc brake, coaster brake or internal drum. The gearing using a larger v-belt driven pulley gets close to the 18/19:1 ratio ideal for higher revving <49cc engines.
    I'm a firm believer in the K.I.S.S. method of building a MB & as a DIY project this solves many issues associated with gearing & one-off expensive parts. The biggest challenge is building a narrow rim for the tire & welding a narrow rim pulley to fit inside the seatstay/chainstay junctions (without bending). Perhaps redishing the spoked rim to offset it closer to the pedal driven side would allow a wider rim for the tire (less pinch flats).
    Last edited: Nov 11, 2008
  8. Nashville Geoff

    Nashville Geoff New Member

    K.I.S.S. is crutial in my book... I'm going to look into fabbing a rim pulley from scratch that's wide enough to handle a belt, and narrow enough to not have interference issues. It might even be set away from the wheel/tire itself. Strength vs. weight, and ease of build... Gotta put on my McGuyver hat.
  9. Egor

    Egor Guest

    Look at the set of plans 4th from bottom, it will give you an Idea of the way it will look. This is a set of plans from and old PM magazine it would be fun to make one. I have been looking for one of the early B&S engines for a long time, they are hard to find now. Have fun, Dave
  10. lowracer

    lowracer Member

    I finished building my simple drivetrain in this fashion & it is posted now on both the new & old Picture Galleries searchable under ' Rocky Mountain RM7 -Super Motard- '
  11. Ls614

    Ls614 New Member

    Did you try looking at whizzer motorbikes? They are very reliable and use a v-belt system. You can get the rim and hardware that will fit on a 26" wheel for around $80 on their website. I ended up buying the GEBE drive ring and then choosing my own pulley and belt from Stock Drive Products. PM me if you are interested in any dimensions on the pitch or diameter of the GEBE hub, it is much cheaper and easier to install. Good luck!
  12. Curby Weaver

    Curby Weaver New Member

  13. Racie35

    Racie35 Member

    Whizzerpaul..... On eBay sells the whizzer sheave and mounting hardware too