A Different Mod....

Lee Shelton

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Joined
Dec 19, 2016
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Hi guys. I've been building my motorized build from the ground up...so to speak. I slapped a 79cc Predator on a 21-speed. I removed the crank, using the bottom bracket to build a jackshaft ( 5/8" shaft 9"L 5/8" presicion bearings [OD 1- 3/8"] meshed int the original ballbearings). NO PEDALING ALLOWED. All was going well until the last two steps - mounting the drive sprockets and drivetrain! Temporarily I wanted to power a gear mounted on the leftside rear wheel. Ultimately, I want to drive the bike gears. My problem is broken down into both short term and long term. The short term problem: The leftside 9 hole - 32 teeth, dished sprocket takes #415H chain but I can't find a 5/8" bore keyed sprocket to mount on the jackshaft.
The long term problem: I can't find any sprocket to mount on the right side that fits the multi-speed bike chain. I need help!
 


Frankenstein

In memory of Frankenstein 1991 - 2018
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Jun 24, 2016
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Also you can turn down a gear on a keyed shaft to fit thinner chains, done it twice. Put the gear on a drive shaft of the right size and make it spin under motor power. Then run an angle grinder along the teeth and body of the gear untill the chain fits well. Take it very slow at first and lightly feel out the danger zone with the angles of contact you can make, some work nicely and others try to rip the grinder from your hand. That being said wear your damn goggles!
 

FurryOnTheInside

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Sep 23, 2013
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Also you can turn down a gear on a keyed shaft to fit thinner chains, done it twice. Put the gear on a drive shaft of the right size and make it spin under motor power. Then run an angle grinder along the teeth and body of the gear untill the chain fits well. Take it very slow at first and lightly feel out the danger zone with the angles of contact you can make, some work nicely and others try to rip the grinder from your hand. That being said wear your damn goggles!
I've heard of this technique in relation to the #415 engine output sprocket, but I think I also read an opinion that it will ruin the hardening and the sprocket will wear quickly.. what have you experienced?
 

Frankenstein

In memory of Frankenstein 1991 - 2018
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5,077
No problems since I don't put the grinder in the teeth and ruin the hardness where the chain actually pulls. Just take it easy and don't burn the metal, took almost an hour last time to slowly run down and fit the chain we were using.
 

Frankenstein

In memory of Frankenstein 1991 - 2018
Joined
Jun 24, 2016
Messages
5,077
Also had to use a belt sander on a sprocket to fit my nuvinci, was too thick a sprocket, if the metal doesn't get so hot you can't grab it for a moment then you aren't getting anywhere hot enough to destroy the temperament, it's like filing but slightly faster.
 

FurryOnTheInside

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Sep 23, 2013
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3,993
No problems since I don't put the grinder in the teeth and ruin the hardness where the chain actually pulls. Just take it easy and don't burn the metal, took almost an hour last time to slowly run down and fit the chain we were using.
Yes I understand that you're only grinding the side, but heat spreads. I have just read this objection and not actually sure if I've read an actual account the experience, so I am just looking for real confirmation that it works well in practice. Have you put many miles on the thinned sprocket?
 
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