3 speed jack shaft

camlifter

camlifter

Active Member
heres the drive for my 4 stroke build,
 

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pretty cool setup , have you done a 3 speed hub before , i,ll be keeping an eye on this one , curious to see how well the hub can take the abuse . how do you start the motor on this one ? ( your drive side of the 3 speed hub probably still coasts ) . is it gonna have a pull start ?

or is your next post gonna say ( homer simpson ) dohhhhh !!!!
 
is that a rollfast/ jc higgens frame with the middle tube removed?
 
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the motor is pull start, the frame is a columbia from the 60's, the gear box is for a pocket bike. i think it should hold up well, the motor puts out much less tq than a person can put to the hub. it's just something i wanted to try, no free wheel crank, and the out put shaft of the gear box is now supported by 2 additional bearings, that should take care of the flexing problem of the hoot type gear box's, this one is a chain drive box.
 
CAM the chain that drives the wheel, Why didnt you go straight to the shaft with a drive gear? It seems it would be simpler and less moving parts plus less loss of power. What was your thinking on this? Im thinking you did this for strength and to cure the shifting of parts maybe as you said, was this the sole reason?
 
bandito said:
CAM the chain that drives the wheel, Why didnt you go straight to the shaft with a drive gear? It seems it would be simpler and less moving parts plus less loss of power. What was your thinking on this? Im thinking you did this for strength and to cure the shifting of parts maybe as you said, was this the sole reason?
Click to expand...

not sure what you mean. if i used gears from the gear box to the 3 speed hub that would reverse the direction. i'm using the 3 speed hub to get more reduction than the 3 to 1 box offers plus getting 3 speeds and no need for a free wheeling crank set. i should have it ready for a test drive in a few days.
 
FANTISTICO CAM! Looking forward to more pics and updates. Really, very cleaver. I was just going to ask how you were going to address chain stretch but on 3rd view of your pics,.. wow, good job

(I wanted to do some thing like that but with clutches that engage at different RPM and freewheels. Would work like an automatic tranny)
 
OK cam let me be a little more precise, in pic 1 it clearly shows what Im asking. The shaft coming out of the gear box is only about 4 inches away from the drive chain that drives the wheel. Just curious as to why you didnt go to that shaft directly with the drive chain that drives the wheel. Pic 3 shows this very well also........nice fabrication and clean install.
 
Maybe the answer is right before my eyes but Im not seeing it. Im not saying the shaft coming out of the motor, the shaft coming out of the gear box. Why is it that he went to a drive sprocket on right side then back to the left side to the drive wheel chain? From the pics it looks like he could have driven the drive wheel chain directly off of the shaft coming out of the gear box. The gear box contains the 3 speed transmission correct? The gear box stays on Im not mentioning to do away with it....how do you shift that gear box between 1st, 2nd and 3rd?
 
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bandito , that hub ( IS ) the 3 speed . and it has to be driven from the right side as it would if it were driven by the pedals . it only works one direction and is likely a coaster brake hub , so it must be driven from the right side of the bike . it shifts by a small chain that comes out of the hubs axle . it has 3 positions , planetary gears .
the gearbox on the side of the motor is only a gear reduction . it doesn,t shift .
 
OK I finally understand, I feel humbled. I thought you could actually shift it from 1 speed to another. TY Diceman.
 
actualy i could be wrong about the gearbox on the side of the motor . its pretty big . earlier in the thread theres mention of a cvt but he says its chain drive it may also have a few gears , 2speed clutch or something , i don,t know . but anyways , thats why the chains are the way they are .
 
Whats the purpose of a gear reduction gearbox if you need to further reduce the ratio with additional sprockets? Im bull headed Im gonna get this answered.
 
The gearbox on the the engine itself is not a CVT- it reduces the engine speed at a ratio of 3:1 meaning that that the output shaft is turning 1/3 the speed of the engine. That is fine if you just want to run that to the rear wheel, but there will be one, fixed ratio- now additional ratios. Why additional ratios? Because the 3:1 reduction is fine for cruising, but very, very sluggish at lower speeds- takes for ever to accelerate. It would be so much nicer if there was some way to have a lower ratio so the engine could turn faster, in its power band, at a slower sped, then some way to change ratios to and intermediate range to continue decent acceleration, then a final ratio to cruise at with the engine not screaming at a very high speed.

Bingo- the 3 speed transmission. Think of it this way- with that three speed, you have the equivalent of 3 rear sprockets- something like an 70 tooth for acceleration at a lower speed, a 60 tooth for intermediate and a 48 tooth for cruising. However, you get all this just in that little three speed hub.
 
Ok Hough I appreciate your input, the output shaft off of the gear box turns at 1/3 the speed of the engine ok. In my mind I know the purpose of the gear box and thats what it does. The purpose of the other 3 sprockets is to change that 3/1 ratio correct? (plus theres the sprocket on the wheel) How does this bike change ratios without changing a sprocket to a different size? I now know why he didnt put the drive chain to the rear wheel directly to the output shaft coming from the gearbox. What is the final ratio between the engine rpm and the rear wheel sprocket with this setup? How does this bike change from a 70 to a 60 then a 48 tooth gear ratio? Im starting to feel stupid.
 
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urrrggggg . bandito . the bicycle hub that he is running between the motor and the rear wheel is a ( 3 speed hub ) . all of the gears are inside that hub . i,m not sure what the gear ratios are ,but lets say for arguement sakes 1st gear is 3/1 , 2nd gear is 2/1 and 3rd gear is 1/1 . the picture attached is what the inside of that hub looks like . i take it you never seen one of these before , they were very common when i was a kid .
 

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oops and before you ask . the gears are changed by a small chain that comes out of the center of the axle hooked up to a gear lever by a cable
 
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