[Kartbuilding] wedling/racing cart

Stephen Burke sburke at burkesys.com
Thu Jul 19 08:51:21 IST 2007

Aye - you might be needing a new rear axle. Any wobbles like a bent rear 
axle would cause the chain to come off the sprocket. Even if the chain did 
stay on, the brake disc and calliper would require a lot of freedom to 
allow enough clearance (to prevent rubbing when the axle rotates).

Onto your transmission.
OK - so you have a 11hp engine at 3600rpm.
Are you sure the rear wheels are 30 inches in diameter!!?? I think thats 
surely a typo. 12 inches (or 30 centimeters) sounds more likely.

I do think that using a ratio of 2.8:1 will burn out the centrifugal 
clutch. Onto the purpose of the kart. What are you going to mainly use the 
kart for? Racing, off-road, general purpose. Will the kart be requiring 
high acceleration on take-off? or high top end speed. Perhaps if the 
centrifugal clutch is rated for a 11hp engine, then it will not wear the 
clutch excessively.

The IDEAL transmission method is to use a "torque converter". This uses a 
variable transmission, giving lots of torque at low speeds, and high top 
end speed.
(In looking for a torque converter on northerntool.com, I came across your 
brake calliper at: 
Here is a torque converter kit -> 
If you have the money, I would definately consider it.

Anyways, even if you do choose to go ahead with the centrifugal clutch, 
you can easily change things afterwards if need be. I suppose you can try 
it and see. What I done to allow me to change sprockets on the rear axle, 
was to cut a quadrant/section out of the sprocket, bolt it to the carrier, 
and then weld the cuts. See:

I know your sprocket has a hub attached already, so this may not work too 
well, but Im sure you get the idea. Otherwise removing the sprocket can be 
quite difficult especially if you have the wheels welded on can be a lot 
of work!

As for the set screws stoping the side to side movement, get some thread 
locking fluid (loctite) which will prevent the set screws from coming 
loose, which you wouldnt want!

As for attaching the sprocket/clutch to the engine, I would advise against 
welding it to the engine. There again should be a keyway that can be used. 
There also should be a threaded hole in the end of the engine's output 
shaft, where you can bolt in a flange piece to stop the clutch from 
slipping off. There should also be a set screw on the centrifugal clutch 
which you can use. But as for welding, some engine shafts are very brittle 
(tempered cast steel etc.) and welds can easily break off.

Feel free to send on whatever photos of the parts you use, and I can put 
up a section on the www.kartbuilding.net website on your kart!

Best of Luck,

On Wed, 18 Jul 2007, Jakub Rogalewicz wrote:

> Ah sorry, I should have mentioned before. My rear axle has a keyway going 
> through its entire span. I need to replace it though because it is slightly 
> bent. I got the front king pin pieces done today. They look really nice. Its 
> good news that the set screws will keep things from moving side to side 
> (thats what I had in mind; the side to side motion). Thats it for now, I'll 
> probably have a lot more questions soon. Thanks for your detailed answers. 
> Oh... what do you mean by saying that the sprocket is too large? This is the 
> sprocket I am moutning on the axle. Its a 28 tooth sprocket and the clutch I 
> will be using (the one going on the engine) has 12 or 10 teeth. Sorry for the 
> misunderstanding. This way I am looking at a 2.8:1 ratio or so. I figured 
> this would leave me adequate acceleration and a top speed of just under 70 
> km/h with a wheel circumference of approx. 30 inches. I figured since the 
> engine is twice as powerful as the usual 6.5 hp then I can reduce this ratio 
> by half to get a higher top speed with out sacrificing acceleration. This 
> ofcourse is just in theory. Do you think that this will be ok, or will the 
> engine not have enough torque to get everything moving... or will it just be 
> really really slow of the start.
> http://www.honda-engines.com/engines/gx390.htm
> That is the engine that im using; there is a torque graph that shows the 
> engines power at certain engine speeds. Maybe you could shed some light on 
> whether the configuration I am planning to use will work or not. (((Is it ok 
> to weld the centrifugal clutch to the shaft of the engine?
> Thanks

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