Watercooled motobicycle help

SouthSideKruizuh

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Oct 13, 2019
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13
Yay! Shift kit!

Your engine will LOVE you for it.

Use a 6t clutch sprocket.
Chain it to a 47t(#25h)jackshaft sprocket.
The 47t is 3.87" diameter, about the same as a 24t(#35) sprocket.

On the right side jackshaft, use a 9t(#35) Sick Bike Parts(SBP) sprocket.
Connect to a 36t outer chainring sprocket, freewheel and crank arm.
Use a 24t inner chainring SBP sprocket.

Your first gear(28t) ratio will be 36.56:1.

Your final gear will be 18.28:1.

38.1mph @ 9000rpm in 7th gear.

For more low gearing, swap in a 14-32 for 41.78:1 ratio.

You could literally climb trees with this stump pulling 1st gear.

Perfection.:)
Yay! I could not figure this out. I am kinda looking for more of a mid range there are some steep hills in my hood but I don't wanna sacrifice too much on the flats😉I think I have a shimano that is close to that I could swap in. I am looking forward to the centrifugal clutch (no more manual clutch) and it being watercooled! So cool. Cant wait to get it all put together and post that first pic😁
 
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5-7HEAVEN

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Jun 22, 2007
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2,105
We can hardly wait!

With this gearing, you'll have excellent low, medium and high speed range.

Many years ago, I had a quality Polini a/c engine.

Its clutch had your bolt pattern, so a tranny wouldn't bolt on.

If I knew then, what I know now, I could've made good use of that engine w/a shift kit.
 
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5-7HEAVEN

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Jun 22, 2007
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2,105
I don't understand. A ratio is just a fraction. A 10 tooth drive to a 40 tooth wheel sprocket reduces to 1:4.
Driven gear divided by drive gear = gear ratio.

40t rear wheel sprocket/10t jackshaft sprocket = 4;1..

The driven 40t spins slowly.

Be aware that a large 36t bicycle"s drive sprocket spins the smaller 18t driven wheel sprocket faster.

18t/36t = 1:2 (or .5:1)when pedalling, not 2:1.
 
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5-7HEAVEN

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Jun 22, 2007
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2,105
If you have 20:1 gearing, your bike will motor away.

If you run your 20:1 gearing thru a 18t/36t bicycle sprockets, gearing reduces to 10:1.....

and your clutch will self-destruct, with the bike not moving an inch on flat ground.
 
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SouthSideKruizuh

New Member
Joined
Oct 13, 2019
Messages
13
We can hardly wait!

Many years ago, I had a quality Polini a/c engine.

Its clutch had your bolt pattern, so a tranny wouldn't bolt on.

If I knew then, what I know now, I could've made good use of that engine w/a shift kit.
Yeah these engines are super hard to find now! Really been wanting to build something water cooled on a bicycle and take it on a endurance test
 

SouthSideKruizuh

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Joined
Oct 13, 2019
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So got an update on my project. Got the engine yesterday yay! Paying up for ups from China was worth it got it in about a week.

20210407_105724.jpg

20210407_105635.jpg


I put it next to a can for size comparison. It's so cute and tiny! Much lighter than the standard bicycle engine. I also found out I can just bore the mounting holes from my old bicycle engine exhaust and it will fit on this everything is the same except the mounting holes on this are like 1mm farther spaced. Stoked about that. Getting a custom made sprocket that is 25h 47t with 1.6875 bolt circle diameter mounting pattern to bolt on a 5/8" jackshaft mount with the same bolt on pattern. That will be a couple weeks. Then I gotta get the sprockets from sick bike parts. Then get the mounts made at the sheet metal shop. But the gears are turning on my project
 

SouthSideKruizuh

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Joined
Oct 13, 2019
Messages
13
I am also curious about this:

20210407_105801.jpg


It's the metal tab there at the top of the cdi. I am assuming this is for the killswitch?
 
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