Simpler lighter HT shift kit winter project under consideration

Discussion in 'Performance Mods' started by Wolfshoes, Oct 12, 2015.

  1. Wolfshoes

    Wolfshoes Member

    A engineering feat unique to the Happy Times (HT) engine is the cohabitation of high speed gears in a dry clutch housing. Since the gears require grease or oil; some engineers creating a bike engine assembly would likely not even tried it since the grease would certainly make its way to the clutch causing it to slip. The surprise it that it works as well as it does. With the clutch and some gear reduction out of the way, a simpler path to the standard bike chain drive system is possible.

    Rather than using a crossover shaft behind the motor, I am looking into going right through the bottom bracket as a sleeve or metal tube around the spindle. Since the spindle and metal tube (crossover shaft) share the same center point, there is no need for sprockets and chain from this crossover shaft (hollow tube) to the spindle on the left side (passenger side) of the bike. Just the one way free wheel clutch would be needed connecting the two in a conventional manner. The only chain needed would be from the bottom of a filed HT motor to a large sprocket assembly free spinning on the spindle (bottom bracket) below.

    Standard size shafting and bronze bushings would be used in the bottom bracket with some lathe and mill work done to convert attachment points to metric as needed. To save money, I am going to convert an existing Schwinn Beach Cruiser having the larger bottom bracket. This will also retain the functionality of the coaster brake. The bike has the attachment points to be converted to multi-speed in the future; but as a single speed, I would at least recover free wheeling down hills. Installing a shift kit on a single speed bike should at least qualify me as being "sick" or at least associate "sick".

  2. Arty

    Arty Active Member

    Can you give us a rough sketch? I'm having trouble visualizing it - but it sounds interesting.
  3. LR Jerry

    LR Jerry Well-Known Member

    A picture would certainly help.
  4. HeadSmess

    HeadSmess Well-Known Member

    soooo... you sorta need a single piece crank BB...

    with a cassette bearing, very large od and id.

    that supports the crossover shafty thing. which has a freewheel mounted...

    and inside that shaft is another cassette bearing, using standard BB sizes, taking the cranks?

    if im picturing it right, sounds feasible. if overly complex.

    or you just gunna mount a big sprocket to the left hand crank (dont say "passenger side" on this site as some countries drive on the wrong side of the road and their cars are all back to front because of it ;)) on a freewheel and drive the cranks that way?

    aye aye aye... wheres the freaking sketch?
  5. Wolfshoes

    Wolfshoes Member

    Using "passenger side" was not the best reference. This summer I was looking at what probably was a older European Tomos motorbike at a local state park. The pedal chain was on the left and the drive chain was on the right being reverse of what I usually see built. In cars of the future, the choice will be there of what side of the driver the passenger want to be on when they help pedal.

    A clearly detailed drawing would take more time than I have right now since my work is somewhat seasonal. There is time to ponder ideas. Looking at the motorbike and seeing what space is available for desired changes, I have an idea what could be done with the Schwinn. Remembering back to the mini bike days of the late 60's, very early 70's and how gearing was done prior to utility engine torque converters; there is ways of doing things in the past that may benefit the newer builds of today. Some bikes in that era were offered with a two speed Comet system. The hardware of this era would not fit a motorbike well, but there is a way to get the two speed overdrive action by using a similar setup. With the Comet system, as a second higher speed drive chain took over, the low speed drive chain would go into free wheel.

    To set this up first rebuild the rear sprocket adapter to accommodate a double action ratchet free wheel.
    The first action to bump start the engine using the momentum of the bike. This would disengage as the bike gained speed from centrifugal force. The second action would be a ratchet free wheel for down hill or as the second speed takes over.

    Next set up the chain tensioner to also act as v-belt pully power take off. This v-belt would drive a pully as part of the bottom bracket, but not directly connected to the spindle. In the Comet system, centrifugal force would engage the second drive chain. With no room apparent for this clutch, The v-belt would have its own manual tensioner connected to cable control similar to the locking HT clutch.
    The v-belt drive power would be sent through the bottom bracket to the right side pedal chain set up with its own free wheel to the spindle.

    In summary, in riding the motor bike, the rear drive sprocket would already be in a locked mode due to low wheel speed allowing a bump motor start. As the bike gains speed using the left chain, centrifugal force would disengage two way lockup at the rear sprocket allowing one way free wheel. When the bike nears top end speed the rider would pull and lock the tensioner cable handle tightening the v-belt and sending motor power to the right chain. As the bike gains speed, the left chain would disengage using its rear sprocket free wheel.

    Riding the bike without engine assist offers the benefit of disconnecting the drive from both the spindle and the rear wheel to bring the pedaling closer to a normal degree of effort. Perhaps the rear free wheel bump start mode could be locked in the open position and the loose v-belt would free up the spindle.
  6. Wolfshoes

    Wolfshoes Member

    Looking at chain alignments of the motor chain to the wheel, it looks possible to pass a bottom bracket attached sprocket on the way back to the wheel from the HT engine. If the spindle was longer, such as on a 4 cycle build, space would be available for the 2nd centrifugal clutch on the right side needed for a late 60's two speed chain setup. The 2nd clutch would have to engage at a lower speed than the 2nd clutch of the mini bike Comet setup. Since a chain saw centrifugal clutch engages at a very low speed, it must be possible to do this. With this type of transmission, one chain would be on the left and one chain on the right with no other chains or belts. Shifting from first gear to second gear and back would be automatic based on the speed of the bike. There would no additional levers for the rider. Factory multi-speed gears of the pedal chain would be supported. Back in the day, this shifting setup was attached to an engine of about 200 cc displacement. Being large enough to be considered a motorcycle engine. To use it with a 66 cc engine, the setup would have to be low friction and very light. So far this is possible. With the larger 1960's 4 cycle displacement, usually a Tecumseh 5 hp, not being the equivalent of the current HT engine; the late 60's era, neck jerking surge when the 2nd speed overdrive kicks in will not be present, but it may still be enough of a gain to be worth doing. I could further speculate that a if a four cycle engine were used in a Comet two speed setup on a bicycle, the engine shaft would need to be on the left side of the bike opposite the pedal crank chain, unlike the Predator engine, which therefore would not work. A traditional old school centrifugal clutch made to fit 1/2 inch chain, not 3/8 mini bike chain, would be less of a spacing problem than a engine with a integrated clutch. It may not be practical to move a 4 cycle engine far enough to the right to permit a single left chain setup. The HT may have the upper hand in that regard.