Utilizing the derailleur gear system?

[duivendyk]

If you look at the output shaft, is it offset laterally from the crank shaft?.If so,there is almost certainly a gear reduction.If that is indeed the case,then with the output sprocket the rearaxle sprocket size and the original wheel diameter known it should not be all that difficult for me to come up with a reasonable estimate of what that reduction is.Also,if you know the direction of rotation of the engine and of the output shaft and they are different you know there is a gear in between.How do you start this thing ?.

 

[kerf]

Talk it apart and count the teeth.

 

[86BG]

just not sure what fluid it uses in there. gear oil?

and what if the bearing seal doesn't seal back?

oh well I'll take it open.

 

[86BG]

ok, I pulled the housing off and one half of the centrifugal clutch is mounted in the engine and the other half comes out with the housing so it's a centrifugal clutch (dry) to wet 5:1 gearbox.

Awesome!!

Time to redo the math.

I'm not at a loss I use these same 30t sprockets on my other projects.

 

[kerf]

Yeah, that 5/1 will give you a good start. Linking to a 4/1 chain drive will give you 20/1, should be about right. You could seal that guy with RTV with a little 90W oil, unless it was grease packed.

 

[86BG]

I counted the teeth at the top gear setting on the bike at the front and rear sprockets and they are 14 at the rear, and 29 at the front, so I entered these values into the gear ratio calculator including the 24 inch tire at

http://www.diygokarts.com/speed-calculator.html

and then guessed until I got the RPM at which the front crank needs to be spinning to hit 45 MPH and it was 1200 RPM, so I divided 6000 RPM by 1200 and got 4.61, which is close enough to the already 5:1 reduction on the engine so I figure if I use the 30tooth 35 pitch sprocket on the bike crank left side and also the left side of the jackshaft and the two 11teeth on the right side of the crank and on the engine output I will keep the ratio 1:1 from the output to the bike crank all will be good.

It'll be close enough anyway, since I still have the range selector on the derailleur to mess with.

sucks though having to make the engine spin around the extra weight of the two 35 tooths, but seems the weight of them would make the throttle lift off smoother - like having a heavy flywheel on a car.

 

[86BG]

I found the bike I'm going to use - the Kulana moon dog cruiser. 70 bucks and any weak points I can reinforced with my welder and some scrap steel.

I just took the engine apart and it turns out there's an electric starter on it.. I thought it was an oddball coil but the shrouds covered up the wiring paths so I wasn't sure what it was. I never worked on anything smaller than 5hp and never a small 2 stroke so I didn't make any assumptions.

If the electric starter works I'm gonna be too excited, because the scooter came with a 7AH battery, which I thought was for the lights only. It still holds a charge, too.

If only I knew what kind of engine it is so I can replace the piston rings while I tear it down to paint it black for the orange bike.

The engine will be on the bike tomorrow.

 

[duivendyk]

Your calculations are incorrect, it takes 653 rpm of a 24" wheel to attain 45 mph,which means a crankspeed of 653*14/29=316 rpm and an overall reduction of 6000/316=19 from the engine crank shaft to bike crank sprocket.You have a 5:1 reduction in the engine itself, so you need another 4:1 reduction divided over the two chain drives.

 

[86BG]

Do you have a javascript calculator or a formula I can input my values in and do tthis math manually?

 

[duivendyk]

No I think what you did wrong was to reverse the sprocket sizes that is 14 for 29 and vice versa.29/14 squared is 4.29 which is about the error.Your calculator is OK,you just have to input the correct numbers!