Quest for a touring clutch to tame the mighty HT MB

Discussion in 'Travelling, Commuting & Safety' started by Wolfshoes, Jan 9, 2016.

  1. Wolfshoes

    Wolfshoes Member

    Rather than bolt the rear sprocket to the rear wheel, perhaps a more quiet, comfortable ride can be attained by selectively engaging the rear sprocket to restore downhill freewheel. In order to do this, starting the engine would have to be addressed. This may not be worth it as a stand alone mod for durability reasons. Some aspects of the change worked well and did show promise to improve the bike; some did not and may not make the design worth pursuing as is even with changes in material. Most of the parts are believed to made from UV protected scrap polypropylene which is a "structural" polyolefin; strong enough to be cast into caster wheels like the ones sold at Menards. One advantage of polypropylene as a material used in the construction of a motor bike is being lighter than aluminum. There is a thin plate in front of the spokes believed to be polycarbonate (ex light truck mud flap). The parts are added to a lathed stock 44 tooth rear sprocket intentionally installed inside out to adjust alignment to the wider sprocket assembly. The mechanism is 1 and 1/8 inches wide fit into a Wally Mart Schwinn beach cruiser. The coaster brake arm has been removed but a modified arm could be installed if another version is made.

    Two latching type one way free wheel arms are installed between the spokes and the sprocket and each swivel on stainless steel bolts having spacers made out of scrap metal brake line. As a one way free wheel clutch used on the rear sprocket; there is promise that it could have a future being made out of low cost, light weight materials and so far, looking durable enough since it only has to make up for the difference in the rear wheel moving faster than the sprocket. The assembly however, also has to take the ongoing drive of the engine, which does not appear to be a strain.




    On the outside of the 44 tooth sprocket, two similar latching arms are installed except without springs pulling them towards the center drive plate. Weight is added for centrifugal force to disengage from full engine starting lock up. This aspect of the assembly works properly engage on its own when the bike is at low speed; start the engine in a normal manner, and then disengage as the bike speeds up. So far so good. The sprocket modification would be workable to this point. As some may have been able to predict; the problem comes when the sprocket slows down and the wheel is turning at a faster rate. The outside latching arms try to engage too aggressively into their center drive plate. Using semi hardened steel reinforcement, the center drive plate holds up well. The problem is the polypropylene latching arm teeth, even with semi hardened steel reinforcement, tend to crush when the mechanism engages to speed up the engine as is common with a bolted on full lock up. It may be possible to a system to hold the latching arms until the wheels reach a slower speed, but I an not going to pursue that design change. Before I disassemble what mods were done to this point, here are some pictures of the attempt.



    Behind the sprocket clutch is a spoke guard made from scrap UV protected sign material, hollow and light weight; probably high density polyethylene; also referred to as plastic cardboard. This guard is held to the spokes with UV protected nylon ties through the linear hollow material leaving a smooth surface facing the chain.

  2. syphonza

    syphonza Member

    Looks good how are you holding the sprocket in place
  3. Wolfshoes

    Wolfshoes Member

    The sprocket can spin on the one way freewheel center drive plate attached with 9 bolts to the hub adapter inside the spokes. The spoke protector behind the chain is a double layer of plastic cardboard sign material installed with the corrugations at 90 degrees from each other for added strength. The 2 outer holes drilled into the sprocket are used for the latching arm swivel bolts. The 3rd added hole pictured is not used.

  4. syphonza

    syphonza Member

    Sorry I may seem pedantic here but what stops the sprocket moving left if you are viewing the bike from behind? I know it can't move right as the wheel is in the way but given a little wear what is to stop it moving left and jumping off it's mounting?

    Ps I like the idea!
  5. Wolfshoes

    Wolfshoes Member

    The free spinning rear sprocket is trapped between two notched plastic drive plates held together by 5 screws. Since the plastic is not a self lubricating type, a small amount of synthetic grease is used.

  6. Nanonevol

    Nanonevol Member

    Brilliant! Love it! Soon someone will manufacture something like this.
  7. syphonza

    syphonza Member

    great thanks
  8. Timbone

    Timbone Active Member

    I have read this several times and I am both fascinated and confused by this project. Please bear with me as, too often, I can be stricken with "forest vs trees syndrome".

    First, I'd like to make sure that I understand the problem you are hoping to solve. I can definitely understand that a clutched sprocket freewheel could be very helpful. Removing the constant drag of the motor chain would help at low speed (pedal mode) and on big downhills where the bike could coast much faster than any top end motor speed.

    Are you addressing both conditions? Looks to me like your centrifugal clutch mechanism will lock the sprocket once it hits a certain speed and the sprocket would be fully locked on a big downhill roll.

    I like your creativity here and I appreciate your patience with my questions. Thanks and keep up the great work!