Need knowledge on Gearboxes

[mafyougrover]

Well I got my old Kart running as its sat for quite some time unfortunately. Its a 6.5 hp clone, runs as solid as when i bought it which is great. had to replace a few parts but shes solid. I now need to know what next. I believe i need a gearbox of some sort. It has a ton of acceleration but very low top end, im guessing 15mph tops for sure but cant start from a stop without burning out. The problem is that i know very little regarding gearboxes in general. I understand (for the most part) know how they work in cars but is it the same for karts? and why does everyone go for a right angle gear box? how do i know what gear ratio i want? and is a gear box going to simply give me 3,4,5 gears? or will i need other things to go with it. i really just need a boost of knowledge on this subject. so if someone would explain everything there is that i should really know about gearboxes (for karts) pros and cons, what to get, what else ill need. I'll forever owe you.

thank you so very much.
Matt

 

[solomon]

Go karts are mainly 1 SPEED. Sounds like you have a really low gear ratio. You could get a TAV which is essentially an automatic transmission in a way, or go with a bike engine that already has the gears.

 

[mafyougrover]

is the easiest thing to do just drop a bike engine into it? or do most take the tranny out of a bike? or what should i really do? i want a few gears, id be happy with two but really would like more. maybe i could do it off a lawn mower? i dont really know but id think you all have this figured out by now lol

 

[solomon]

You would have to change the sprocket and weld a mount for the bike engine. You cant take the transmission out of a bike engine so it all stays together as one.

 

[Doc Sprocket]

Let's start with the basics. I'm going to assume you have a centrifugal clutch. Now- you said your top speed sucks, and you can't get off the line without laying a strip of rubber. At the most basic level, your gear ratio is too low. So your first, (and cheapest) option is to regear. Since your clutch has a fixed sprocket size, you are left with the option of replacing your axle sprocket, with a smaller one (less teeth on it). If you furnish us with the tooth count on your clutch and axle sprocket, as well as rear tire diameter and an approximation of the kart's weight with you in it, we can help you calculate a more appropriate gear ratio, as well as a projected new top speed. Pics would also be beneficial. Changing to a larger rear tire would have a similar effet to moving to a smaller rear sprocket.

A pricier option would be a CVT (Continuously Variable Transmission). Also known as a Torq-A-Vertor or TAV, this is a belt driven transmission that smoothly and automatically transitions between different gear ratios to suit conditions. This is a large improvement over a single ratio. You may be familiar with snowmobiles, these use them as well as some trikes and quads, and even some newer cars.

Top of the heap? A bike or quad engine with a manual or semi-auto transmission. This will require a very stout frame, and fabricating skills, but will make plenty of power and give you the ratios to use it to it's fullest.

Cheers- Chris

 

[mafyougrover]

wow toystory 4wd! thank you so much. i really appreciate you passing on all that knowledge to me! tomorrow i will definitely get measurements of my sprockets and wheel and put up a picture making it all easy to understand. there was a website i came across that equated all of that but it was for karts with a transmission and mine (at the moment) is only a 1 Speed. but let me get this straight.....so you cant just pull a tranny out of a motorcycle? or a dirtbike, snowmobile, or lawn mower? and put it on my kart? id need the whole engine?

thank you very much!

 

[devino246]

wow toystory 4wd! thank you so much. i really appreciate you passing on all that knowledge to me! tomorrow i will definitely get measurements of my sprockets and wheel and put up a picture making it all easy to understand. there was a website i came across that equated all of that but it was for karts with a transmission and mine (at the moment) is only a 1 Speed. but let me get this straight.....so you cant just pull a tranny out of a motorcycle? or a dirtbike, snowmobile, or lawn mower? and put it on my kart? id need the whole engine?

thank you very much!

bike engines have a built in tranny. You cant just pull of the tranny and stick it on a kart. Most lawn mower trannys wont hold up to high speeds, plus they'll only work with a vertical shaft engine.

 

[Kaptain Krunch]

motorcycles normally have the engines and transmissions built into the same case. Snowmobiles use CVT's, which are unusable in a kart, and overkill unless u use the whole engine. Lawn mower transmissions generally take of a decent amount of space, require some fabrication, and most are very weak/cant be shifted on the go very well.

If you would rather just attach a tranny to your stock engine, some atv's use seperate transmissions, however using a complete motorcycle, quad, or snowmobile setup will give you much better power.

 

[mafyougrover]

so my only option for a tranny is to drop an entire bike engine in it? or is there a good alternative and not super cash heavy?

 

[devino246]

You could do what im doing, although it takes alot of fabrication. Dont know if you'd call it a good alternative, but it should work. http://www.diygokarts.com/vb/showthread.php?t=7915

 

[mafyougrover]

the physics behind that baffle me lol. i really dont fully understand how that will work lol but looks legit. wishing it was on my kart haha. or some type of tranny

 

[devino246]

the physics behind that baffle me lol. i really dont fully understand how that will work lol but looks legit. wishing it was on my kart haha. or some type of tranny

Its very simple really.

 

[mafyougrover]

toss me a good explanation then lol. id love to understand it better. isnt something supposed to expand as the speed increases due to centrifugal momentum?? or something along those lines? it doesnt look like that would happen though when looking at it. or i may just be way off

 

[fowler]

what that is is a 2 speed gear box in simple terms
what it acctually is, is 2 belt tensioner clutchs together
u engange one at a time
u would engage the inside one first to get speed then disengage the first and engage the second to acheive a higher speed

haveing differant sized pullys works the same as differant sized sprockets (it affects speed and power)

 

[devino246]

I woulda explained it last nite, but was too tired to explain it

 

[fowler]

yeah i cant be bothered sleeping now even if it is 11:00pm

 

[mafyougrover]

what that is is a 2 speed gear box in simple terms
what it acctually is, is 2 belt tensioner clutchs together
u engange one at a time
u would engage the inside one first to get speed then disengage the first and engage the second to acheive a higher speed

haveing differant sized pullys works the same as differant sized sprockets (it affects speed and power)

ya i understand that. how would you "disengage and re-engage" between the two though? so are they belts so that it lowers weight? why wouldnt you want to go chains and sprockets? i feel youd lose a ton of power off the line with belt. or maybe belt for higher gear but chain for lower. or maybe its easier to disengage with the belts? but literally how would you disengage and reengage? sometype of clutch on for both on off of the shaft?

YIKES. looking at the pictures again of your project Devino... holy hell that thing must have some serious low end haha rippa!

 

[devino246]

It uses a belt tensioner style clutch. The belts are kept loose around the pulleys. Which ever ratio you want, you just tension that belt. It should be similar to driving a manual car; Rev the engine a little and slowly let your foot off the 'clutch' pedal.

7.4:1 in first and 2.5:1 in second. The engine doesnt have a gov so it can rev high enough in 1st for a smooth shift in second. I calculated all that stuff out. disengage 1st @ 6000rpm & engage 2nd at around 3500rpm. Something like that. In messing with/reving the engine, it seems it should have no problem winding down from 6000 to 3500rpm in the time it would take to shift(mabe 2 sec?)

 

[mafyougrover]

that sounds really smart and well extremely simple. should make for very smooth shifting. great work man. now i have so much more respect for it. i may end up doing that if getting a tranny is out of the question for my finances.

 

[Kenny_McCormic]

You could use a Harley-Davidson motorcycle gear box, these have a clutch built in with 4-6 gears. Unfortunately you will pay more than a good Japanese motorcycle engine pushing 50+hp with a built in transmission goes for. Keep in mind all motorcycles are unsynchronized constant mesh dog boxes so you shift them like a race car(as fast as possible), a little different than driving your mom's civic.