My first kart project

[chris609]

Here is my first kart that will be a gift to my soon to be 4 year old. I got the body off ebay she went nuts when she saw it. I am in the process of welding a simple frame for it. I will be using Azusa steering spindles, 6 inch disk brake, 12 tooth clutch,60 T sprocket, 79cc predator with new filters and new exhaust that I need to weld up. and other things I cant think of now. Here are some pics
I'm sure I will have lots of questions as I proceed. Thanks

 

[landuse]

Here is my first kart that will be a gift to my soon to be 4 year old. I got the body off ebay she went nuts when she saw it. I am in the process of welding a simple frame for it. I will be using Azusa steering spindles, 6 inch disk brake, 12 tooth clutch,60 T sprocket, 79cc predator with new filters and new exhaust that I need to weld up. and other things I cant think of now. Here are some pics
I'm sure I will have lots of questions as I proceed. Thanks
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Thats a nice body you have there. What size tyres are you going to use. I ask because I am a bit concerned about your gear ratio. With a 60T and a 12T, you are going to have a ratio of 5:1. That is quite tall, and with your small engine, I am seriously worried that you are going to run into problems. You will be burning your clutch pretty fast.

 

[OzFab]

I disagree, that ratio will be ok as long as there's a 3:1 reduction jackshaft inbetween! Firstly due to landuse's point above, secondly because that much speed will scare the pants off a 4 year old.

The beauty of a jackshaft is you can easily regear it as she gets older & more confident

 

[chris609]

Hi all i will be using 11" tires i was thinking of torque converter or jack shaft and i cut the back out to make extra room the motor. So is a jackshaft the best route to go?m y little one will be 4 when it is complete i wanted to keep speed low anyway. What is the best gear setup for jackshaft? Thanks

 

[chris609]

O.K I have been looking around for info on jackshafts what sprockets would I use then for a 3:1 reduction? I am getting confused maybe this info will help. 12 tooth max torque clutch, 60 tooth axle sprocket, 79cc 3600 rpm engine, 11'' diameter tires. High speed is not desired now I was planning on simply blocking the throttle or peddle. Any suggestions? Thanks

 

[mysteryboy28]

you need to study the jackshaft calculator and the speed calculators below.

first figure out what you want your top speed to be. then figure out what the highest RPM of the motor is. then figure out what gear ratio you need with the 11" tires you have. for example: say you want 10mph top speed. the speed calculator says with 11" tires at 3600 rpms you want 10t on the clutch and 120t on the axle. that obviously won't work with 11" tires. lol. k now you go to the jackshaft calculator and try some different combinations (always keeping the engine/clutch sprocket at 10t). with 11" tires you will want to keep the axle sprocket pretty small, like 40t or so for some ground clearance.

http://www.diygokarts.com/speed-calculator.html

http://www.fasttrackraceway.com/calc/

and seriously, why not use a 212cc Predator? you will be really unhappy with a little 79cc. by gearing it low now for slow speed - you will have the easy option of gearing it higher as she gets older, without really losing much horsepower. 79cc is just not gonna cut it when she's 8 and wants to go 30 mph! lol. plus the resale value will be much higher for when the day comes that she loses interest in the kart.

oh, and a torque converter is WAY better than a centrifugal clutch. more expensive, yes. but totally worth it for performance and endurance.

 

[chris609]

Thanks for the info I thought about the 212 predator but thought it might be to big to fit. I think I will check into these torque converters. Thanks for the info

 

[OzFab]

A jackshaft with a 28t & 13t sprockets will give you a ratio of 11.67:1 & a top speed of 10mph.

IMO:
-You will have the same problem with a CVT as you're having now, you'll still have a high top speed unless you incorporate a gearing jackshaft.
-A 212cc Predator will have massive torque with law gearing which, again, will be daunting for a 4yo
-By the time she's 8-10, the kart you're building now will be getting too small for her & will require major mods anyway. At that point, a new kart may be in order

My 9yo daughters kart has similar gearing & a 3hp B&S. Granted, she hasn't been driving it for 5 years but, she loves it

 

[mysteryboy28]

a motor too big to fit? that's preposterous! there's always room for a bigger motor. lol.

 

[chris609]

Good point fabroman I have been messing with the calculators mysteryboy posted and some others I found. The jackshaft setup is how I will go now it is making more sense to me. I will fab a mount of some kind this is getting even more fun. Good point too on building another when she is older I still hope she will be a tomboy and mess around in the shop with me. Cool pic mystery I thought of burning my 20% off coupon on a 212 but I have lots invested in this one. Thanks a bunch everyone for helping me along

 

[mysteryboy28]

can't use a 20% off coupon on motors at harbor freight. they do have $99 coupons all over the web though.

but yeah, for her little kart with all that gear reduction you will be fine with a smaller motor and a centrifugal clutch - as long as the kart isn't too heavy.

oh, and you don't have to put a reason for editing your post. lol. i just edited this one, and i refuse to put a reason. lol.

 

[landuse]

I disagree, that ratio will be ok as long as there's a 3:1 reduction jackshaft inbetween! Firstly due to landuse's point above, secondly because that much speed will scare the pants off a 4 year old.

The beauty of a jackshaft is you can easily regear it as she gets older & more confident

But if you have a 3:1 reduction inbetween the 12T and 60T, then the ratio won't be 5:1 anymore, which is what I was saying is too tall.

 

[OzFab]

Dude, I was actually agreeing with you but being a smart a** about it

He'll still have a 12t clutch & a 60t axle sprocket but with the facilities to change the ratio at any point in time so, technically, my point stands

 

[landuse]

Dude, I was actually agreeing with you but being a smart a** about it

He'll still have a 12t clutch & a 60t axle sprocket but with the facilities to change the ratio at any point in time so, technically, my point stands

I guess I am still half asleep. I have a terrible head cold and am not feeling too great.

Sorry man

 

[OzFab]

No probs man, hope you feel better soon

 

[mysteryboy28]

I guess I am still half asleep. I have a terrible head cold and am not feeling too great.

Sorry man

hopefully it's not ebola, being in africa and all...

 

[landuse]

hopefully it's not ebola, being in africa and all...

Sheeesh. Next you guys will be thinking that there are lions running around free in the streets, and that we ride elephants to work....

 

[hsr]

Can you guys help me understand this better please? The calculator on this site http://www.diygokarts.com/speed-calculator.html states that 11/12T clutch with 60T is one of the most common ratios. That was the OP's starting point.

landuse,

You said that will cause clutch burning issues. Because of small power engine? With 11" tire, that's only 24mph.

I understand how the calculators work. I'm just trying to understand if you guys were trying to find a way to get the top speed lower due to the age of the driver? Or the engine won't have the torque to get the kart rolling?

Mysteryboy28,

Here is the HF coupon I was planning to use. It doesn't say anything about engines in the fine print. http://www.harborfreight.com/20off-coupon912-aff-17547.html I'm also in Michigan. Is this new stipulation they put on the coupon use?

Thanks for the info guys,
Jeff

 

[mysteryboy28]

Sheeesh. Next you guys will be thinking that there are lions running around free in the streets, and that we ride elephants to work....

aren't there, and don't you?

 

[mysteryboy28]

Mysteryboy28,

Here is the HF coupon I was planning to use. It doesn't say anything about engines in the fine print. http://www.harborfreight.com/20off-coupon912-aff-17547.html I'm also in Michigan. Is this new stipulation they put on the coupon use?

their engines fall under their generators category. their computer cash registers simply will not accept a 20% off coupon for an engine. so instead use this coupon: