Jackshaft gearing

kartboy63

Member
I never ran a jackshaft before, we are going to a big block and I picked up a jackshaft , how do you figure out the gearing and is there a chart out there somewhere ?
 

spincycle

Member
Jackshaft primary side 57/21....secondary side 19/64.... that's on a hi revving 2 cycle engine with a 3disc clutch on the secondary side...
 

paulkish

old fart
I never ran a jackshaft before, we are going to a big block and I picked up a jackshaft , how do you figure out the gearing and is there a chart out there somewhere ?

Below is a picture of my gear chart. Works with both non and jackshaft. You only input green area and the additional gear and ratio's automatically fill in. I open it with open office office .org free software. With it you get to look through columns of different clutch and axle gears for a close ratio match or to go with a little more or less gear. We ran mini gears on the axle which is why the small axle gears in the first chart. The only change I made to get the second chart was to put 53 into the 'green' axle gear input and hit enter.

In the last one I just threw in some numbers for a clutch on the jackshaft output with chain going back to the axle.
 

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paulkish

old fart
Here's the last ones with some hypothetical numbers thrown in.
 

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Jim46

Member
It will help with long chain problems ( jumping chain) , I would suggest using a belt from the crank shaft to the Jack shaft Short chains get hot , put your clutch on the Jack shaft, that gets the clutch away from the driver and easier to get to the clutch, belts don't need oil or much maintenance
 
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