2 Speed Transmission



Hi All,

Just doing a little searching online and came across this 40 CC gas scooter with a 2 speed transmission (Stand on Goped Style not the large sit on ones)...Hard to tell from the pic but being that it is sooo small it must be able to fit easily on our bikes....Is this the solution?...Anybody have any idea how they make it work?...Here is the link to the page I looked at: http://www.trendtimes.com/evo-gas-scooter.html
I wonder if this setup can be bump started?
Thanks Alaska....I looked at the manual but my brain still cant figure out how it works...I think it must work like the 2 speed jackshaft in another post on this board but even then i'm
not sure how how that one works either....Thanks for the post tho. This one looks like
it can't bump start but would probably help those of us who have recoil start and need a 2 speed.
It is the exact same concept as the 2 speed jackshaft, except it is all belt driven instead of chains, which would make it a lot quieter. It would also be a nice, fully contained system. The problem with this set up (besides mating it to your engine, which may or may not be easy, I don't know) is that you would have to have 2 belts going from the transmission to your rear wheel.

Heres how the concept works described in words only. A picture would be better. I'm good mechanically and at drawing, but scanning/downloading/computers in general are frustrating (I already deleted this whole post once). Here goes:

1. The transmission (or jackshaft from the other thread) has a main shaft with three pulleys attached to it (sprockets in the case of the jackshaft).
2. Pulley #1 is run by a belt from the engine, this is what turns the main shaft.
3. Pulley #2 is attached to the main shaft with a freewheel type mechanism. If the shaft is turning then pulley #2 HAS to turn. Pulley #2 runs a belt goes to a pulley on the rear wheel and drives the rear wheel. Typical type drive system so far, except the freewheel.
4. Here's the interesting part, pulley #3 is attached to the main shaft with a centrifugal clutch type mechanism. This allows the main shaft to spin WITH OUT turning pulley #3. At this point #2 is the only thing driving the rear wheel. However, as the RPM's of the main shaft increase, it reaches a point at which the centrifugal clutch engages and pulley #3 becomes powered up by the main shaft.
5. Pulley #3 has a larger diameter than pulley #2 (more teeth in the case of the jackshaft) and is attached to the rear wheel with its own belt (seperate from pulley #2, they each have their own belt going to the rear wheel). The larger diameter of pulley #3 causes the rear wheel to spin faster than #2 would drive it.
6. At this point pulley #2 starts working as a freewheel and #3 is the pulley driving the rear wheel.

That is as clear as I can describe it, hope it helps.
When I started reading the description, I got myself all ready to end up being clueless. Very well explained! I totally get it. What rpm do you figure the clutch is turning when it engages?
Thanx! You nailed this explaination (hope this word is spelled correctly, LOL!) very well! I wonder if this design could be developed to a three speed.....
Wow...Thanks KeepOn!....I fully understand it now!....I really had no idea before but you really did a good job with the wording (I'll admit it I drew a pic based on your wording to help me visualize it).....Very tricky until it's all broken down.....unfortunately, as far as I can tell, this would still not allow a bump start since pulley/sprocket #2 is on a freewheel...Ofcourse if one could devise a method to selectively enable or disable the freewheel mechanism on sprocket #2 or....

HEY I may have just thought of the solution.....OK I hope I can word my thoughts as well as you but to make it bump startable imagine that Pulley/sprocket # 2 has a hole in it (on its side all the way through it)...Now place another disc (Call it Disc 2A) and spline or or welded onto the same shaft as pulley/sprocket #2 (it always spins with the shaft) in between pulley/sprocket #2 and Pulley # 3 with the centrifical clutch mechanism (need not have teeth or grooves in it) BUT simply a hole through it....NOW to bump start the engine one can take a "pin" to go through the hole on pulley/sprocket #2 and Disc 2A
and fire up the engine....(hold in temporarily w/ nut and bolt or a cotter type pin), then after engine fires, remove the bolt or whatever was used to lock Pulley/sprocket #3 to Disc 2A and motor away!.....As a side benefit, nobody cam motor away under engine power without the startup "pin".....
Think that'd work?....as far as I can think I think it would but I may have overlooked something.....of course with recopil start the bump start of the added disc would not be needed.
I like the idea of automatic and at least 2 speed.
Now the key would be to use this same concept to build a smaller chain or gear(they are narrower than belts for the same HP) driven device based on the same theory using a centrifugal clutch to bridge the step from low(1st) to high(2nd); and small enough to fit below the chinese bicycle engine, but instead of both(the 1st and 2nd) connected to the rear wheel, to have them both connected to a jackshaft and from there to the rear wheel with only ONE chain.
I am sure it could be designed as a 3 speed(using one more centrifugal clutch and gears or chain system), but it would begin to grow in size, weight and rotating mass.
But again I am open to the idea. So far 2speeds would be relatively cheap to build and bullet proof compared to internal hubs I think.
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Oh...Note: to pull the pin out separating pulley # 2 from Disc 2A in order to allow Pulley #2 to freewheel after starting the engine, the clutch has to be pulled in and the bike has to be motionless for obvious safety reasons.
Andyinch, yes your idea might work. Somehow we have to start those butstart engines. I did'n think of that.