DIY motorized bike missing gear

Jul 2, 2008
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I have a Giant Revive. I have found a good electric motor from a scooter that is a small frame and have everything that I need to make a pedal assist bike. I am unclear as to what gear I need for the motor. I know that I need one with a couple set screws but the gears that I have found online are called #25...

What gear for a bicycle chain do I need to complete this? The shaft for the motor is about a 1/4 inch in diameter. I am placing the motor in front of the pedals and running the chain from the front gear over the motor shaft with this gear on it... the one that I do not have...

Any help is appreciated.
 

Easy Rider

Santa Cruz Scooter Works
Jan 15, 2008
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Nor*Cal
I think the 25 stands for the chain size. A 25h or 25 chain is used on electric scooters. If that's the case you could use a large pocketbike cag sprocket. Pipelyne carrys a bunch of those sprockets with lots of different sizes.
 
Jul 2, 2008
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I am putting my motor inline with the chain that is already there... it is intended to be a peddle assist. Do you know what number the chain that is on a bicycle is? If #25 is a pocket bike, does a regular bicycle have a certain number? I look and see that my chain is just the same as all 10-26 speed bikes as in the size but before ordering the sprocket for the motor, I wanted to make sure that i have the right one. Thnks for the site information btw. I will look there now.
 

deacon

minor bike philosopher
Jan 15, 2008
8,117
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north carolina
the width of the sprocket will be thicker on a 41 than a bicycle chain. I have never seen a number for a bicycle chain to be honest. They are just 1/8 x 1/2 or maybe it is 1/2 by 1/8 mtb chain is a little thinner. 3/32 I think. If you weld you might just weld a bike's rear sprocket to the drive of the elec motor. You would have to weld a washer to the rear sprocket to decrease the size of the hole, then weld the washer to the motor hub.

Personally I would just use a friction drive. But then I'm less mechanical than most here.
 
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Goat Herder

Gutter Rider
Apr 28, 2008
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Not fretting at you Joe but Between a 5speed 9speed is a differant chain size. Somthing about the added sprockets in the rear, the extra steps in the sprocket sizes on 9is diff than the 8 through 5. [ for the derailer that is]. Requiring differant chain size. Funny though you can use the same front sprockets in all cofigerations of chains, and rear cassets.
 
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Goat Herder

Gutter Rider
Apr 28, 2008
6,248
11
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O i got that wrong Chain diff changes at 9 tooth sprocket. for derailers. If I remmember right
 
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deacon

minor bike philosopher
Jan 15, 2008
8,117
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north carolina
Just for some additional confusion, if you decide to switch out the rear wheel of a mountain bike for a coaster wheel. A good think if you mount an engine on the rear wheel and lose the brake, you can use a coaster chain on the slightly smaller front sprocket set, I put mine on the middle sprocket. It helps to keep it from jumping ship I think.

Just some useless trivia.