First Kart Project

[Doc Sprocket]

What are your plans for clutching/gears? If you use a CVT, that 6.5 should do pretty good. If you go centrifugal, I think you'll have to gear down more than you'd like to get any kind of "zip" taking off- which of course will hurt your top end...

 

[nerfo]

Man, that thing's looking pretty good so far! I like the hinge setup you have on the swing arm... it's simple and it looks plenty strong. And the fatties on the back do look way better! The last couple weekends I havn't managed to get anything done... life keeps getting in the way... Taxes have been filed, so tax return = tires and wheels. Looking forward to that! So far so good though! I like it!

 

[thechief86]

What are your plans for clutching/gears? If you use a CVT, that 6.5 should do pretty good. If you go centrifugal, I think you'll have to gear down more than you'd like to get any kind of "zip" taking off- which of course will hurt your top end...

sorry for being such a noob, but how does one put a cvt on a go kart? i figgered i was pretty much gonna be limited to the centrifugal clutch on my own yard kart....

 

[Doc Sprocket]

Oh, HE// NO!!! Do yourself a huge favour and Google "CVT" "Torq-A-Verter" and "Comet 40". Those may not be the only choices available to you, but a dang fine start, and a good source of info!
A cvt is a Constantly Variable Transmission. It uses (typically) A self adjusting driver pully, a belt, and a self-adjusting driven pulley. The "gear" ratios it attains (within it's range) are based on engine speed and load. And at idle, it's disengaged. You need no seperate clutch. It automatically varies the ratios according to conditions, and in short will allow you to have a decent final drive ratio, yet still enough oomph for takeoff. Completely automatic, stab the throttle and go.

 

[thechief86]

sweet! i'll look into that right now! thank you! i was familiar with cvt's on cars, but in my experience with my mazda protege, it kinda sucked. i'm guessing it will be better on a kart, though!
EDIT: that looks very cool, but i think i'll stick with the centrifugal clutch for the time being, as the cvt is more expensive than my whole kart cost!

 

[Doc Sprocket]

What'd your kart cost? Typically CVT's run $150-$300. You might even be able to peel one out of a junked snowmobile, cheap.

 

[thechief86]

ha, the kart was freeeee.......
as for snowmobiles, i live in tennessee. i've never even SEEN a snowmobile anywhere besides tv! i'll prolly get a cvt eventually, but for now i'm trying to stay under $100 bux for the whole kart after installing this 'race' engine i got off ebay, and some new tires. after my roadtrip this summer, i won't be so pinched for cash, so i can get a little spendier then...
i feel kinda bad about this hijack, though..... this guy has a lot of work into his, and he's trying to show it off, so i guess let's get back on topic.

 

[Doc Sprocket]

Thats okay, the info may be useful to Strato, or even someone else viewing the thread.
Whaddya mean there's no dang snowmobiles in Tennessee? LOL

 

[bajagokart]

most comet 40 series give you and added 2.7:1 ratio! in my case i have a 10T sprocket on my jackshaft and a 60T on the axel, this is a 6:1 ratio! multiply the 2.7:1 ratio from earlier, 2.7 * 6.0 = 16.2:1 ratio! this is your starting out gear ratio, low end. now when your engine gets up to its governed limit of 3600 rpm, the ratio has changed from about 2.7:1 to just under 1:1. this is what we call overdrive and it is what gives your go kart the advantage high end power! so when im starting out my ratio is 16.2:1 and when its in overdrive it is 6:1! that is the beauty of a torque converter and they work great on a offroad go kart because the give you a million times better control over a centrifugal clutch!

 

[Doc Sprocket]

I think I'm at 5:1. But- I was sure the 40 was non overdrive. Gonna have to look that one up. Either way, they're lovely!

 

[Kaptain Krunch]

Snowmobile torque converters will be very very hard to set up on anything but a sled engine. The driver clutches on sleds are taper fit, and the driven are either splined, or sometimes 1" bore. Even if you got past the taper, these clutches are meant to engage at a pretty high RPM, the clutch on my Jag doesnt engage till at least 3000rpm.

 

[thechief86]

do they go back down to the low end torque pretty well when you slow down for curves? i'm on a yard kart with no suspension, so i'm not too hardcore offroad, but if i can get some low end torque when i finally can afford one of these things, i'd like to put some bigger tires on the kart, to absorb a little shock, and help out with ground clearance. i may down the road set up at least a rear suspension similar to what strato has goin on there, and incorporate a roll bar into the frame so i can have a good solid spot to mount the shocks.

 

[thechief86]

strato, can we get a close up of how you did the hinge apparatus on the rear end?

 

[Doc Sprocket]

Yes, they react very well. The kart I'm using right now I did not build, I bought it as an instant gratification thing until I build my own. I didn't know a blessed thing about CVT's 'till I got it, and I consider my Comet 40 to be the next best thing to a gearbox. My kart (see avatar) has a GX340 and some decent sized rear turf tires. My final ratio is aournd 5:1. I may lower that slightly, but nevertheless I am quite pleased with the CVT. Takeoffs are smooth with a light foot, and if I punch it, the debris flies. Donuts, drifting, and powerslides are impressive, as are transitions between high and low roadspeeds.
And yes, the next step for this thang is some suspension. I was getting jostled right out of my seat offroad, so one of my mods was a seatbelt. So far I haven't done much else- kill switch on steering colums, halogen headlight on rollbar, padded boat set (was just plywood before <OUCH!> and I changed the brake pedal to immediately left of the throttle for right-foot-only operation.

 

[Doc Sprocket]

Okay, homework done. The 40 driven unit makes 1:1, the 44 driven unit has a better low ratio of 2.83:1 (as opposed to the 2.43:1 of the 40), but maxes out at 1.24:1, which is a slight underdrive. A TAV30 will achieve a .90:1 overdrive.

 

[bajagokart]

Ya nevermind the 30 series asymmetrical was a overdrive but still the point is if you are going to fast for your liking anyway you can always gear down! What is a gx340? I'm guessing it's 10 or 11 hp? I can't wait to see what my 13 hp clone does with my 40 series!

 

[Doc Sprocket]

11hp Honda. Love it, starts first yank even in the cold, always runs flawlessly! I just wouldn't want to pay replacement costs if I ever blew it up! And-
Never too fast- If it WAS possible, I'd just get off the throttle.
I did a test in the fall that revealed to me that at WOT in a straight, engine RPM's never reach 3600. The kart's rather weighty, fairly hefty tires, 5:1 final ratio. As I see it, I have two choices to attempt to hit (and then subsequently exceed) max RPM- I can either try to adjust the CVT to engage highest ratio later, or gear the kart down a little to lighten the effective load.
Since I'm still unclear about what I can and cannot do with the CVT, I think I'm best to gear down a little. Then, once I'm hitting a governed 3600, I will consider pulling the governor for greater RPM and top speed. With the load in question, I have absolutely no fear of blowing anything up without the governor.

 

[bajagokart]

thats what im thinking im gunna do! i have a 13 hp powerfist clone w/ electric start! im currently in the process of bringing the key up to the front and romote rigging the choke but ive tested the starter and this thing starts no problem at all! once i get my TC rigged im gunna see how fast and how good it runs before i even look at taking that governor off

 

[Stratogeezer]

Thats okay, the info may be useful to Strato, or even someone else viewing the thread.
Whaddya mean there's no dang snowmobiles in Tennessee? LOL

Hey guys - no worries - this is useful about the CVT to me as well. I think the first go-round I'm going with the standard centrifugal - but that (and the 6.5 engine) may be swapped out after time. I too am a bit stuck on the CVT pricing - just because all the other piece parts are running up my total costs pretty well already. But - sounds like CVT would be the best option over time for sure.

 

[Stratogeezer]

strato, can we get a close up of how you did the hinge apparatus on the rear end?

Sure thing - here's two close-ups of the hinge section - one looking from the front and one from the back.

The hinges are quite strong - I modified a couple of brackets from the trailer aisle at Northern to fit nicely on...after some heating, bending and hammering into shape. I also welded the bejesus out of them. to the frame.

However - here's were I goofed, and realized later... I should have positioned those 2 hinges as far apart as possible, versus their current position, which is about 5 inches inward on each side. Should still be ok, but worst case is I install a 2nd set if needed.