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bike4life

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You may want a larger input gear on your jackshaft to get a higher gear reduction before your pedals. Most folks look for around 40:1. If below 30:1 you won't be able to help pedal other than just off the line for a few feet. Here is a link to a gear ratio calculator one of our members made. Remember to have your first reduction for your engine set to 20:82 then work from your 10 tooth output to the jackshaft input for the second, then jackshaft output to pedal chainring. You can then work out your chainring to rear wheel, if using multi-speed then you can figure out your 1st gear and last gear speeds at specific rpms. Have fun, looks like you are on home stretch.
PS: stop trolling yourself :LOL::p.
OK. I am a little confused. Currently I have a 10t engine sprocket which leads to a 10t jackshaft input sprocket. The jackshaft output sprocket is about 10t (not yet installed in the video) and this leads to a standard 40t sprocket on the crankset [pedals]. Isn't this normal. Like if i set my derailleur at a 1:1 gear ratio to the crankset, this would be equivlent to if i had no jackshaft at all as if i just mounted a 40tooth on the rear wheel. What do i need to change. Plus i cant open this calc. msi file. BTW I couldn't find any large gears that are compatible with the engine sprocket except those replacement engine sprocket gears which is what i used. If you have a link let me know.
QUICKY: The engine pistons rotates at 5000rpm but you have to multiply it by 20/82 which means the actual 10t engine sprocket is 1200rpm????
 
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bike4life

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Mar 19, 2018
Messages
441
Jungle Pig. For your peace of mind, I know a welder in Queens NY that I can visit and show him. Both parents have no clue about welding and my moped project. I am not a completely beginner welder, I have burned 5lbs of rod so far in my life. I am confident that those welds will hold. I am doing stick welding so its a little stronger and screw up proof than mig. I used E6011 so it will penetrate deeply. Basically its a rod that even if you suck at welding, it will be strong because it digs into the metal rather than glues on top of it. I am worried though if the chain explodes or catches on my jeans. Soooo I am gonna build a box around it.
 

CrazyDan

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OK. I am a little confused. Currently I have a 10t engine sprocket which leads to a 10t jackshaft input sprocket. The jackshaft output sprocket is about 10t (not yet installed in the video) and this leads to a standard 40t sprocket on the crankset [pedals]. Isn't this normal. Like if i set my derailleur at a 1:1 gear ratio to the crankset, this would be equivlent to if i had no jackshaft at all as if i just mounted a 40tooth on the rear wheel. What do i need to change. Plus i cant open this calc. msi file. BTW I couldn't find any large gears that are compatible with the engine sprocket except those replacement engine sprocket gears which is what i used. If you have a link let me know.
QUICKY: The engine pistons rotates at 5000rpm but you have to multiply it by 20/82 which means the actual 10t engine sprocket is 1200rpm????
Yes, the china girl has internal reduction under the right side cover. The way you are currently going you will only have a 16.4:1 reduction at your pedals, yes you can gear it to the rear wheel for acceptable speeds but you won't be able to help at all. At 2000 rpm you will have to pedal 122 rpm to assist your engine. Thats already too much at just above idle to help pull away from stops.
 

bike4life

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Messages
441
Yes, the china girl has internal reduction under the right side cover. The way you are currently going you will only have a 16.4:1 reduction at your pedals, yes you can gear it to the rear wheel for acceptable speeds but you won't be able to help at all. At 2000 rpm you will have to pedal 122 rpm to assist your engine. Thats already too much at just above idle to help pull away from stops.
Ok. So I need a larger gear on the jack shaft input side. Probably what like 20tooth.
 

CrazyDan

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A 20 tooth there will bring it up to a 32.8:1 reduction at your pedals allowing you to pedal at 61rpm when your engine is at 2000rpm. It would be tons better getting a high reduction before hitting your pedals. From the pedals you can adjust your final gear ratios to the back wheel for the speed you want.
 

bike4life

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Messages
441
A 20 tooth there will bring it up to a 32.8:1 reduction at your pedals allowing you to pedal at 61rpm when your engine is at 2000rpm. It would be tons better getting a high reduction before hitting your pedals. From the pedals you can adjust your final gear ratios to the back wheel for the speed you want.
Thx Crazy Dan A LOOOOOOT. Although I regret I didn't ask this question earlier b/c now I have to remove my 10t gear that I drilled a 5/8" hole in. Thankfully I didn't weld it on yet.... lol. I was always curious on how ppl pedaled with a jackshaft but now it all makes sense. I didn't realize that the gearing stepped down the 5000rpm to a measly 61. I always thought the actual freewheel sprocket spun at like 500rpm which is god level if a human could match that therefore adding to my confusion.
 

CrazyDan

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Well 5000 rpm with a 32.8:1 reduction at the pedals puts it at just above 152 rpm. You would need even more reduction if you want to pedal your full engine rpm range. If you used a 9 tooth output on your jackshaft and a 44 tooth on you chainring input you would have a 40.089:1 reduction at your pedals, which would only require you to pedal at 124.7 rpm to pedal with your engine spinning at 5000 rpm. Using that ratio you have another 44 tooth chainring going to the back wheel. Using a 34 tooth to 14 tooth cassette on the rear wheel you will have a 30.978:1 overall reduction for first gear and will hit 12.485 mph at 5000 rpm if used on 26" wheels, and last gear will be 12.756:1 for 30.32 mph at 5000 rpm. Of course if your engine can spool higher then you can travel faster. At 7000 rpm in last gear you will be going 42.448 mph with a 26". Your wheel size will change rpms at certain speeds, a larger wheel will accelerate slower but have a higher top speed than a smaller wheel. Hope this helps.
 

bike4life

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Well 5000 rpm with a 32.8:1 reduction at the pedals puts it at just above 152 rpm. You would need even more reduction if you want to pedal your full engine rpm range. If you used a 9 tooth output on your jackshaft and a 44 tooth on you chainring input you would have a 40.089:1 reduction at your pedals, which would only require you to pedal at 124.7 rpm to pedal with your engine spinning at 5000 rpm. Using that ratio you have another 44 tooth chainring going to the back wheel. Using a 34 tooth to 14 tooth cassette on the rear wheel you will have a 30.978:1 overall reduction for first gear and will hit 12.485 mph at 5000 rpm if used on 26" wheels, and last gear will be 12.756:1 for 30.32 mph at 5000 rpm. Of course if your engine can spool higher then you can travel faster. At 7000 rpm in last gear you will be going 42.448 mph with a 26". Your wheel size will change rpms at certain speeds, a larger wheel will accelerate slower but have a higher top speed than a smaller wheel. Hope this helps.
But what is the best rpm to run your engine. You know the upside down U graph that shows rpm and torque and power. The spot right before it declines or the 2 curves intersect. OK AND ON
 

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CrazyDan

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Those 2 stroke engines are easy to tune for where you want power by lengthening or shortening the header on a tuned expansion chamber. As I understand a longer header puts your power band in low-midrange, with a shorter header you make max power up in the higher rpms.
 

bike4life

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Messages
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Those 2 stroke engines are easy to tune for where you want power by lengthening or shortening the header on a tuned expansion chamber. As I understand a longer header puts your power band in low-midrange, with a shorter header you make max power up in the higher rpms.
Crazy Dan. Thanks a lot for the data. After 1 hour I created my own gear ratio calc that can be viewed by anyone with an internet connection. NO DOWNLOADS MSI FILE CRAP. https://docs.google.com/spreadsheets/d/1ClO9FVzFxwQoJLvGGkv1O_3_qPanuesK6YTL-_pN5Xg/edit?usp=sharing
 
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