Help with 2 speed auto for 79cc

Jan 21, 2015
610
23
18
Portland, Oregon
A while back I tried to build a 2 speed manual trans for my 79cc bike, I have since scrapped the idea. I want to build a 2 speed auto instead, but I really have no idea how to go about doing it. I have seen pictures of them made using 2 centrifugal clutches, but don't know how to do this. Can anyone walk me through it?
 

Tony01

Well-Known Member
Nov 28, 2012
1,422
907
113
sf bay area
Post 7 in your thread, search for my thread 3+ speed jackshaft, MSRfan 2-speed. You can buy a complete 2-speed from blackwidow motorsports for $300 I don't remember the link. Also see my riding video.

The base cost for parts will be around $150 no matter what method you decide to take. I'm working on a prototype 2-speed with a planetary gear set, however base cost for parts alone will be something like $200 and I can build you one for around 400 or even more depending on the access I can get to machinery, and because of all the design, machining and welding work. But it will be very efficient, single jackshaft, one chain from engine and one chain to sprocket, like a single speed setup. Also with the available springs for MT clutches you'll need to have a final chain reduction of almost 6:1, I have 10 to 56t sprocket to get reasonable shift Rpms. Or if you want, you can buy my twin Js 2-speed for $250 so I can jumpstart my prototype. Warning, it is difficult to setup and you must have sufficient frame space.
 
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Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
How about the SRAM 2 speed automatix rear hub with a shift kit? I've heard that you can adjust their shift points with little intrusion, and that they're pretty stout as well.
 
Jan 21, 2015
610
23
18
Portland, Oregon
Post 7 in your thread, search for my thread 3+ speed jackshaft, MSRfan 2-speed. You can buy a complete 2-speed from blackwidow motorsports for $300 I don't remember the link. Also see my riding video.

The base cost for parts will be around $150 no matter what method you decide to take. I'm working on a prototype 2-speed with a planetary gear set, however base cost for parts alone will be something like $200 and I can build you one for around 400 or even more depending on the access I can get to machinery, and because of all the design, machining and welding work. But it will be very efficient, single jackshaft, one chain from engine and one chain to sprocket, like a single speed setup. Also with the available springs for MT clutches you'll need to have a final chain reduction of almost 6:1, I have 10 to 56t sprocket to get reasonable shift Rpms. Or if you want, you can buy my twin Js 2-speed for $250 so I can jumpstart my prototype. Warning, it is difficult to setup and you must have sufficient frame space.
I would prefer to build one myself rather than buying one premade.

I have read the thread by MSRfan, and would like to try something like that, however I do not think that I have enough information to replicate the transmission, nor the knowledge to fill in the gaps. Does anyone know the exact centrifugal clutches he used? Or how to go about figuring out which other clutches would fit the bill? Is the rightmost chain in this image http://s1047.photobucket.com/user/msrfan/media/2 SPEED/DSCN5894_zps2d68e74a.jpg.html necessary if I have a pullstart?
 

Tony01

Well-Known Member
Nov 28, 2012
1,422
907
113
sf bay area
I would prefer to build one myself rather than buying one premade.

I have read the thread by MSRfan, and would like to try something like that, however I do not think that I have enough information to replicate the transmission, nor the knowledge to fill in the gaps. Does anyone know the exact centrifugal clutches he used? Or how to go about figuring out which other clutches would fit the bill? Is the rightmost chain in this image http://s1047.photobucket.com/user/msrfan/media/2 SPEED/DSCN5894_zps2d68e74a.jpg.html necessary if I have a pullstart?
he used max torque #35 single and dual sprocket clutches. you don't need the pedal start chain.

what was wrong with your dog clutch transmission?

Agreen, the SRAM is a piece of junk with only a 33% gear jump and tiny little components that will break fast with an engine.
 
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Jan 21, 2015
610
23
18
Portland, Oregon
he used max torque #35 single and dual sprocket clutches. you don't need the pedal start chain.

what was wrong with your dog clutch transmission?

Agreen, the SRAM is a piece of junk with only a 33% gear jump and tiny little components that will break fast with an engine.
MSRfan mentions a special one way bearing and shaft. Can you explain how that works? Can I just use the two clutches without special bearings if I don't have the pedal start chain? If not, any idea where I could find said bearings and shaft?

As for the dog clutch, I was unable to machine parts accurately enough in my garage to get it working properly.
 

Tony01

Well-Known Member
Nov 28, 2012
1,422
907
113
sf bay area
Read through my thread it's all in there. It's the same as an rc car 2-speed and the 3-speed is he same concept as the Kyosho 3spd. First gear freewheels and 2nd when engages at some rpm overrides the first gear.

Reason why I said the best way is to buy it is cause there is no easy way to build your own. If using dual sprocket clutch it is 35 chain, good luck finding a 35 freewheel. Msrfan had a custom shaft and sprag clutch made to work. The dual sprocket clutch on his is the main engine clutch. He set it up like that to emulate the whizzer setup where the main clutch is on the jackshaft so that he could pedal start it. My trans has the main clutch on the engine which drives a jackshaft with two sprockets solid mounted on it mechanically the same as a dual sprocket clutch. But by making it on a jackshaft I was able to use a 41 sprockets and a regular bicycle freewheel which is easily replaceable and cheap, and no fabrication required. READ my thread!!

But if you went to the blackwidow link and looked at that 2-speed, it comes with the dual clutch and a machined adapter and shaft similar to msrfans.

If you send me your email address I can send you a video of how it works and the design limitations.
 
Jan 21, 2015
610
23
18
Portland, Oregon
Read through my thread it's all in there. It's the same as an rc car 2-speed and the 3-speed is he same concept as the Kyosho 3spd. First gear freewheels and 2nd when engages at some rpm overrides the first gear.

Reason why I said the best way is to buy it is cause there is no easy way to build your own. If using dual sprocket clutch it is 35 chain, good luck finding a 35 freewheel. Msrfan had a custom shaft and sprag clutch made to work. The dual sprocket clutch on his is the main engine clutch. He set it up like that to emulate the whizzer setup where the main clutch is on the jackshaft so that he could pedal start it. My trans has the main clutch on the engine which drives a jackshaft with two sprockets solid mounted on it mechanically the same as a dual sprocket clutch. But by making it on a jackshaft I was able to use a 41 sprockets and a regular bicycle freewheel which is easily replaceable and cheap, and no fabrication required. READ my thread!!

But if you went to the blackwidow link and looked at that 2-speed, it comes with the dual clutch and a machined adapter and shaft similar to msrfans.

If you send me your email address I can send you a video of how it works and the design limitations.
Buying may be easier, but what fun is that?

I took another look at your thread, and I'm starting to understand how this works. Do you have any more detailed pictures of your setup that I could look at?
 

Tony01

Well-Known Member
Nov 28, 2012
1,422
907
113
sf bay area
if you can avoid it don't do twin jack shafts. The efficiency loss is ESPECIALLY apparent in top speed with the 3-4hp motors we have. I think with single js you can top out at 50 on the regular. I'm getting bored with mid 40s. Just did another ride today approx 20mi round trip. Always wishing for more hp and top end, despite my already tall gearing.

Not many pics, which part you wanna see?
 
Jan 21, 2015
610
23
18
Portland, Oregon
if you can avoid it don't do twin jack shafts. The efficiency loss is ESPECIALLY apparent in top speed with the 3-4hp motors we have. I think with single js you can top out at 50 on the regular. I'm getting bored with mid 40s. Just did another ride today approx 20mi round trip. Always wishing for more hp and top end, despite my already tall gearing.

Not many pics, which part you wanna see?
Do you have a good closeup of your gearbox where you can see everything clearly?
 

Tony01

Well-Known Member
Nov 28, 2012
1,422
907
113
sf bay area
Not really cause it's on opposite sides of the seat tube. There is nothing but flange bearing protrusion between the plates. Here's a pic of the right side.
 

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