cheap go kart build: the engine and clutch

[michaelr123]

hey everybody, i know i sorta double posted here, but the other topic isn't to do with my go kart build, any way, now that we have that out of the way, on to another issue i have.

me and my friends are getting together to build go karts that we can race together and just have fun with for under $300. i've pretty much got it figured out, but i do need a little help on the clutch and engine.

i want to use the predator 212cc which is on sale right now for $120! its 7hp and a great engine as i've heard on many reviews and youtube videos. one of my friends says we can get away with the 99cc and save some money.

my thinking is that the 212cc will be much quicker and easier to get running fast enough while making it a single gear system. where as the 99cc could work, if we get the gear ratio just right and split it into a high and low gear, which i think is way harder and more expensive than just buying a more powerful engine and setting the gear ratio more towards top speed and just using the straight horse power to give it the acceleration we want.

as for the clutch, i literally want the cheapest clutch i can find that will still work, i know the shaft is 3/4 and i want to use number 40 chain because that's what i have left over from my last build. can i find centrifugal clutches at say, the junk yard?

as for gear ratio with a predator 212cc, i was planning like a 2:1 or 3:1, meaning for every spin on the engine shaft, the back wheels would turn a 1/2 or a 1/3 of a rotation. i used a calculator for speed and got 45 and 38mph with 10" wheels like i want to use. so a 10t on the clutch and a 20-30t on the rear shaft? will this result in pretty good acceleration? me and my friends are all around 160lbs and we are keeping the go kart super small and light, i'm guessing under 300lbs total for sure.

any help is greatly appreciated from the one on this build that is figuring everything out!

 

[Doc Sprocket]

You definitely want something more than the 99cc. It's doable, but anemic. I guarantee you will not be satisfied with performance.

Your gearing calcs are too steep. Your sweet spot will be around 5:1 or 6:1, not 3:1. Ratio calculations are theoretical, and do not take into consideration many factors including available power, and clutch tolerance. 3:1 will burn out your clutch, and accelerate very poorly.

You may be able to find a clutch at a junkyard, but it won't be easy. Truth be told, you have to be VERY resourceful to build a kart for $300 or less.

Were you guys planning on scratchbuilding?

 

[michaelr123]

we are using the school tech lab (entire machine lab and welding available to us, and most importantly, the teacher said we could use it and she'd be willing to help)

we're building virtually everything from stock steel to cut down the price, also my 3 wheel design cuts out almost everything to do with a live axle which helps a lot. check out my post in the go kart forum for the run down, i can post my design on this thread too if you like.

and for the gear ratio, thanks a bunch, do you think a 50t will fit with within a 10" wheel gap? i guess it will just look like a mini bike a little bit lol. if the number 40 chain sprockets are a little to big we could maybe step down to #35...

 

[landuse]

I would definately not go with a 99c engine. I will be too weak.

Your gearing, like toystory says, is waay too high. IMO you need at least 6:1. This will give you decent acceleration. I would buy a cheap centrifugal clutch (approx. $40) instead of trying to find one at a junkyard.

For a 6:1 ratio, you will need a 10T clutch and 60T axle sprocket. If you go with a #40 chain, the 60T sprocket will have a diameter of 9.84". This will not leave you much clearance room with 10" tyres. A #35 60T sprocket will have a diameter of 7.38". This gives you a lot more clearance room.