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Old 05-03-2011, 05:15 AM
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Default 60+ tooth #40 sprocket

i just got done the other night at dark with my kart build, its a dead axle manco, it was an indy car, i took the body off and put 13" front and rear tires on it for more clearence for off road. Im using this kart in my 2 acre yard, pretty flat, a little grade in spots.
A couple weeks ago i finished my daughters kart, i got this one for me where i can keep her company and have fun racing around our yard.


Anyway i only got to drive it for about 10min so far bc of all the rain, it has a stock un goverend 5hp briggs, 10t hilliard clutch, 60t rear. Me and the kart are probably around 400lbs. It seems to pull decent in the yard, but i could use lots more torque and less speed in the yard.

I took it down the street and noticed i could feel the clutch lock up and the kart accelerating more as the engine tone changed(dropped), but i cannot achieve that speed in the yard where i will be driving it, and i dont want to burn the clutch bc its not locked.

Im not looking to do a jack shaft or a tav rite now.
Anyone know where to get a 66-72 tooth sprocket for #40/41 chain? My hub pattern is 4 on 2-13/16"


Also since i have the hilliard extreme, would it be better to change to lighter springs so the clutch locks sooner where it wont be slipping?
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Old 05-03-2011, 08:49 AM
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I've got a feeling that carefully measuring with a digital caliper, would reveal your sprockets bolt pattern is actually a 4 on 2.875".

If so, you'll find your find your sprocket here:--> http://www.gokartgalaxy.com/shifter_...kets_for_1.htm

Here's a link to a #40 sprocket diameter chart you could use to make sure your larger sprocket ends up with sufficient ground clearance:--> http://www.azusaeng.com/Sprockets/AzSDno40.pdf

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Your clutch came with a 2300-rpm lockup. That's probably the rpm-level where your engine reaches its maximum amount of torque, and that's exactly where you want your clutch to be locking up. So I'd suggest you try a larger sprocket before altering your clutches lockup rpm.

Lowering your clutches lockup rpm would probably end up causing even more clutch slippage because of your relatively low-powered engine and fairly heavy cart load. So if anything, I'd go with a bit higher lockup rpm to help keep the engine at its torque-peak during lockup...
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Old 05-03-2011, 05:30 PM
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Thanks anderkart, thats exactly what i needed to know.

I was able to do more riding today, and i think it does pretty well with the 10/60 setup for what im asking, but it could be better.
If i do go with a 72t its saying its 11.75" and on my 13" tire, (i need to verify true height first) is going to give me 5/8" clearence.

a 70t is giving me rite around 3/4" clearance
a 66t is giving me a tad over 1"

What is a good rule of thumb for sprocket to ground clearance?
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Old 05-04-2011, 09:44 AM
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So yeah that's a very good point. There's no carved in stone rules about how much clearance you need between your sprocket and the ground.

If you only rode on perfectly flat pavement with fully inflated/stiff sidewall-ed tires, you might get away with as little as a 1/4" of clearance and never contact the ground. On the other hand, with off-roading over big ruts/bumps/rocks: you could have 6' of sprocket clearance and still be contacting things and forcing dirt into your chain causing problems...

Even with your current 60 tooth rear sprocket you've only got 1-1/2" of clearance to the ground now, and that's not the best situation for an off-road type kart. Your 60-tooth and chain are most likely hitting rocks and trenching into the dirt now as you drive over most any uneven terrain. Obviously any larger sized sprockets is going to worsen this situation.

But I'm thinking you could probably just simply install a 72-tooth, and not have to many more issues than you might already be experiencing with your 60.

You've already got the smallest 10 tooth clutch driver-size available so... the only other alternative to achieve further gear reduction (without an even larger rear sprocket) would be with installing a jackshaft setup similar to this first pic below:

You could install a much smaller axle sprocket (like a 35-tooth...) and then achieve any gear-reduction you wanted by carefully selecting your jackshaft gear sizes.




If you dont want the hassle of installing a jackshaft, you could do what I do to help protect larger sized sprockets (and your chain) from constantly hitting rocks and trenching through the dirt. And that's install sprockets guards like mine pictured below.

Here's a 66 tooth/#35 sprocket (with 11" tall rear tires) and a factory made sprocket guard installed. You can see the sprocket and chain are fairly well protected from direct contact with the ground:



But then I wanted even lower gearing (and taller tires) for the little dirt-oval track I race at, so this pic below is my 84-tooth sprocket w/13' tall rear tires... Instead of buying a new jumbo sized sprocket guard, I simply bolted on a couple old wore-out 86-tooth sprockets I already owned to function as my sprocket guards:

(another huge advantage of using sprocket guards is they make it nearly impossible for your chain to come off...)
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Old 05-04-2011, 02:14 PM
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anderkart...... nice tecumseh... is that a H60? if so where did you get a billet rod? ive been looking and havent found anything.

also whats with that tube coming out of where the dipstick normally is?

tecumseh flatheads are awesome.
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Old 05-04-2011, 02:34 PM
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What about putting the sprocket very close to the tire so that it would be very difficult to his the sprocket as the tire would most likely take the bump.
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Old 05-04-2011, 10:59 PM
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Quote:
Originally Posted by Bluethunder3320 View Post
anderkart...... nice tecumseh... is that a H60? if so where did you get a billet rod? ive been looking and havent found anything.

also whats with that tube coming out of where the dipstick normally is?

tecumseh flatheads are awesome.



Its called the Star engine. Back in the 1990's Tecumseh made 1000 of these 357cc. engines just for open-class kart racing. They were loosely based off the H100 but even the block was shorter, narrower, lighter and stronger. They came with all kinds of trick parts including a forged rod, and were sold disassembled in a kit form, that was intended to be blueprinted or further modded at speed shop before final assembly.

They run on methanol and develop between 20 and 40hp depending on the mods done. Some guys add a bit of nitro and get up to 50hp from these...

Tillotson designed a brand new carb just for this engine that was included in the kit. Noram also produced a new 'Star' clutch model designed for this engine.

They dont have recoils, you have to use a electric kart starter due to the high compression and radical cam profile.



Most all Star engines used that dipstick tube as an over-sized breather port, and then installed an automotive PVC valve because the high-compression/strong pulse signals caused most all the oil to puke out the little/stock breather tube in the valve cover:



The 3/8' breather hose is then connected to a puke tank with a filter like this:

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Old 05-04-2011, 11:09 PM
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Quote:
Originally Posted by redsox985 View Post
What about putting the sprocket very close to the tire so that it would be very difficult to his the sprocket as the tire would most likely take the bump.
Good idea!
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