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Author Topic: belts and pulleys  (Read 848 times)
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banit2026
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« on: December 24, 2013, 03:02:11 PM »

I have started work on a build like Georges mod single with a 420 predator. It will remain stock for a while until every thing is working properly. No for the first question, Why can't I run a belt from the motor to the jack shaft and then put a shoe clutch on the output side of the jackshaft? Do you use the mower pulleys or say something from tractor suppily? What sizes would you suggest? What size belt, A or B ? Any input would be greately appreciated!! confused2 confused2
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2nstoys
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« Reply #1 on: December 25, 2013, 03:07:51 PM »

This has been discussed in other threads but I will give my 2 cents. #1. You can run a belt, but you would need to run it at almost a 1 to 1 ratio for the jackshaft to spin fast enough for the clutch to work properly on the other side. #2. If you have no reduction on the primary side then the secondary side would need to have a huge reduction to be able to get to the speeds you will need to be running.

On my 2 machines the primary ratio is 2 - 1. So, say the clutch engages at 3400 rpms, and the redline of the engine is 7000. The jackshaft is only spinning 3500 rpms at redline. A 1-1 ratio would have the jackshaft spinning the same rpms as the engine and good luck finding decent bearings to handle that kind of rpm. Secondary ratio varies, but is in the 3 or 4 - 1. Gives final ratios of 6 thru 8 to 1. To get that on one of the drives is a big jump in sprocket sizes. Hope this helps.
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banit2026
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« Reply #2 on: December 25, 2013, 04:15:23 PM »

As it stands now the seciondary side  12 on the clutch and 72 on the axel or 6 - 1 ratio. If I run 1 to 1 on the primary side and stay around 5000 rpm, why would it not work? With the torque of the engine and depending on tire size it should rattle on pretty good.  What would be the difference if I put the clutch on the engine and run a chain instead of a belt to the primary side of the jackshaft?
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heymow.com - Lawn Mower Racing Forum
« Reply #2 on: December 25, 2013, 04:15:23 PM »

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fx28
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« Reply #3 on: December 25, 2013, 06:55:58 PM »

 No matter where your clutch is mounted the way you want to do, it will work fine. It will turn same rpm on crank as jackshaft. I have seen some open class karters do this for many years.   1 to 1 on primary is fine as long as you can get your ratio on secondary.   A width belt will work fine, you will however need to run at minimum 4" to 5" diameter pulleys to reduce slippage.  While it might seem more economical running belt, there is some power loss and also depending on location of jackshaft the diameter of pulleys could become a clearance issue
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banit2026
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« Reply #4 on: December 26, 2013, 10:03:18 AM »

I haven't totally given up on running a chain from the motor to the jackshaft, right now I just looking at the options and parts avilability. Right now I have access to a scrap yard for 35 cents a pound. Thanks for the input as thats what I needed, a little reinforcement.
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Egoracing
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« Reply #5 on: December 28, 2013, 06:34:01 AM »

Are you talking about chain on a vertical shaft motor? Chain is made and designed to run with the sprockets vertical, if you run them horizontal the chain will be hanging on the sprockets and will wear the chin and sprockets out very quickly.
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banit2026
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« Reply #6 on: December 28, 2013, 12:00:47 PM »

I know what you are saying, they will be vertical . Check out Georges super modified single. This is what I'm aiming for. I'm still collecting parts. got some exhaust pieces today. I'm stripping an old sprint go cart I got in a trade, so axel, steering, gears and brakes are in hand. Just want to get every thing lined up before I start cutting and welding. I hate waiting on parts. 
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