need help with my belt drive train

Mr.GhettoRig

Mr.GhettoRig

Member
so After scratching my head long enough I've finally decided to ask for help.

I'm setting up a belt drive for my electra build (http://motorbicycling.com/showthread.php?p=446984#post446984) with a suicide lever that engages and disengages the belt.

My first question is about the gear ratio, I wanted to make sure that the pulleys I have now are adequate enough to get the bike moving. diameters are...
Engine: 2.75
Jackshaft-in: 3.625
Jackshaft-out: 3.5
Whizzer sheave: 15
wheels: 26

Also I'll be generous and say my engine tops out at about 4,000 RPM.. (5hp briggs with shaved eyebrows, cleaned ports, header, and a tec 5hp carb. I believe they are normally governed down to 3,500 stock.)

according to this calculator ( http://www.fasttrackraceway.com/calc/index.php ) I have a final ratio of 5.65. but I dont exactly know what that means? Is that acceptable?

And my second question is how tight does the belt need to be on the engine to jack shaft during idle and drive? I plan on using a flat idler pulley on the bottom (slack) side of the belt, as I read on here that requires less tension to get the drive to work. I'm just unsure of how much slack to give the belt during idle, and how far up to move the idler pulley for belt tension.

This is new to me so any and all help is appreciated. Thanks in advance.
 
I would recommend a ratio of 10:1, but anywhere between 8:1 and 12:1 should work. You usually have to try different combinations to suit your needs and terrain.

I use a cvt clutch, so I don't know about using an old style lever tensioner.

Gilbert
 
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thanks for the input guys, how do you calculate the ratios? the online calculator I posted just spits out a number, but what does the number mean? Is it that number to 1? In my case it spit out 5.65 so 5.65:1 ratio?

Also the terrain here in southwest florida isn't too hard to compete with.. most of the roads here are smooth and hills are a rare sight. I'll aim for a 10:1 ratio as Gbrebes said, since thats right between 8:1 and 12:1.
 
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would someone please delete this post? I still can't figure out how to do it myself.
 
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Just following along out of interest. This seems close to what I'm hoping to build. Glad you finally decided to ask!
Can you post some pics when you start testing?
Thanks
 
Trey said:
Just following along out of interest. This seems close to what I'm hoping to build. Glad you finally decided to ask!
Can you post some pics when you start testing?
Thanks
Click to expand...

of course! You can also see some of my mockup pics on my build thread too. (link in first post.)

I'll stat the fabricating when I get more new pulleys. still not really sure about the tension but I'll cross that bridge when I get there.

good luck with your build.
 
Checked those out- nice. The suicide lever is a must (local statutes allowing). Planning this build for fall, plenty of time to stea- I mean borrow your plans!:)
Thanks.
 
well I ordered two new pulleys, went with a 4 on the jackshaft in and a 2.25 on the out.. which puts my final ratio at 9.70:1 its not 10 but its above 8 and should be a lot better than the 5.65 I had before. I'll let you know how it goes when I get the bike together but that still looks far off in the distance.

any input on the tension part? I'm especially concerned with how tight the idle tension needs to be so I don't throw the belt or have the bike in drive when I'm stopped. the bike will be on a center stand with the rear wheel in the air so I'm not worried about it when it parked just when its on the ground and stationary. I think with the drive tension I may have to set up a fully adjustable mockup and test it out until I get what I need, then go back and secure it all together for good.

still could use any and all input though.
 
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