a Crossfire kart RestoMod

[firemanjim]

You dont have to have hi/lo gearbox to have fun or get out of trouble. You're using an atv engine (250cc) too with a gearbox. First gear should be sufficient for you to get out of a whole, as long as you know how to drive. Using a 4x4 atv is a cool idea,BUT too expensive for me at the moment and a lot of fab work...... lol would be awesome though. ....

 

[firemanjim]

Ok so i have 11 teeth ,#41 series, on atv engine. The axle sprocket is 31 teeth,#420 series...... guy i bought engine from says the frame has a 38 tooth sprocket. When i buy the gears for the jackshaft, I think I want to use this combo.... atv= 11t ... driven sprocket =13t turning a 10t drive sprocket to the axle sprocket of 31t... Im not good with the ratio math so some help would be great. I am trying to now make up a little torque lost due to my kart axle sprocket is 7t shorter than the atv sprocket was. I will be using a 1" axle and pillow block bearings to build jackshaft.
While im at it, I know my chains will end up being different lengths so I assume adjust so motor to jackshaft chain has proper tension, and if need be ,I made a chain tensioner for the axle chain to make sure its always snug. Does this sound right?

 

[landuse]

I am not too good with ratios when it comes to engines with gears. Sorry

 

[OzFab]

Punch some numbers into this

However, why not just use the 11t & 31t? With multi gears, it shouldn't be too bad...

 

[firemanjim]

After playing with numbers, thanks Fabroman, I guess I'm going to just go with the 11t atv to 31t axle with 11's on both sides of J/S . At 2.8:1, it should be cool since I have the high and low gear sets. I can always play with it later.

 

[firemanjim]

ok, I finally got the info I've been looking for, but am now lost. Taking all of the following info into consideration: 200e atc engine gear ratios, both high and low. Primary reduction 3.333* Final reduction 4.273* 1st 2.769*2nd 2.722*3rd 1.273*4th 1.000*5th 0.815 ~~~ posi-torque gear ratio 1st 3.835*2nd 2.386*3rd 1.763*4th 1.385*5th 1.129~~~~ The original atc sprocket sizes are 11t and 47t , my karts p/o WELDED the current sprocket onto the axle. (A LOT of WELD) That sprocket is only 31t .... Originally I wanted to get more speed out of the low gear set, but thats a HUGE difference between 31 & 47 teeth. Now I think.i need to put more low end to it. If your good at this type math, can anyone tell me what sprockets to get for the J/S to get me back closer to the original final drive ratios? I think with a 31t I'm going to be losing a great amount of low end "grunt", ya know?

 

[itsid]

I'm sorry I might be wrong on this, but why the math stuff at all.
You have 11:31, and you want 11:47 (since that is what you intend to change right?!)

final ratio target: 1:4.272727
final ratio currently: 1:2.818181

4.2727 / 2.8181 = 1.5161 (target jackshaft ratio)
for example a pair of 11 & 17 sprockets on the jackshaft (1:1.545454)

ends up in Final Ratio: 4.36
engine 11, js in 17, js out 11, axle 31

18/12 for Final Ratio: 4.23
17/12 for Final Ratio: 3.99

etc.

'sid

 

[firemanjim]

Thanks itsid! That kinda clears up the whole thing for me. I didn't even need all those ratios I looked up.lol... Your explanation gives me what I need to know to "play" with ratios down the road.

 

[firemanjim]

Update,... well, no real update... lol Finally got some more welding wire today. I think i finally got the chain size and sprocket counts down. Going from a 520 to a 530RO chain. (Motor is 520 axle sprocket 530)I found some angle iron the right size to make frame extensions. I'll be workin on that tomorrow while at work and also start laying out my daughter's new kart project. Gonna start a build thread for that one tomorrow when i have pics. Tonight I spent an hour disassembling her donor quad. Got a great idea , using a lot of the pieces to really make something cool..... can't wait.