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Old 09-17-2018, 12:43 AM
bulby bulby is offline
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Default Gear what? Clutch that? TIRES?!?!

Hello,

I'm new here as a member but not as a viewer. I've been combing through the internet looking for an answer to my question but haven't found it so I figure you guys can come up with one.

I'm wanting to build a go kart and I've got an Ironton 420 (northern tool predator). I need advice on how to build/gear the drivetrain. I have a 1" bore 14T centrifugal clutch laying around that I'd like to use to power it so I don't have to buy a TC. The kart is gonna be a "scale model" (I say it like that cuz we'll see how close it'll actually be) of a particular car, and it'll have ~13 in rear tires. I'm hoping for a speed of atleast about 30.

It'll be a yard/street/beach kart, live axle.

The engine is gonna stay stock, mostly. Its a non-hemi so any mods are gonna be swapable to an eventual hemi. NON-governed, stock, these motors run at what, 4000, 4300 rpm? So lets say 4000 rpm, 13 in tires. Will a 6:1 ratio be enough reduction for the clutch? That's only 25 mph so any more gearing will be even slower. (I know I'll probably need a jackshaft)

So basically 6:1 is as low as I'll go. Will I burn up the clutch? Or should I go straight to a TC?

Thanks
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Old 09-17-2018, 05:41 AM
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stock engine speed is 3600,

check the manual closely if the governor can be readjusted to a higher speed,
but assume 3600.
run it ungoverned ONLY if you remove the governor internals!
(don't just bypass the linkages)

sticking with 3600 rpm:

6:1 ratio with a 14T clutch is likely not going to work in a single stage reduction

but maybe it's not needed..
on a lightweight kart ~250lbs or less (and weight is important!!)
a 5:1 ratio should work as well thanks to the torque your engine has
so 70T on the axle should fit
and should yield almost 28mph

maybe you even can go a tad higher if your clutch is of high quality
a 4.64 ratio (65 teeth axle sprocket) would give you the 30mph you're asking.

BUT testing that could burn your clutch in short order which means you will have to buy a new one.

allowing for ungoverend speeds (5000 rpm)
a 5:1 ratio will keep the clutch alive (70T axle sprocket)
and should give you about 38mph of top speed.

if you want to play with some numbers yourself:
take your phone and go to app.kartcalc.net (the quickcalc is what you are heading for )

'sid
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Old 09-17-2018, 06:34 AM
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Are we talking 13" OD or rim size???
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Old 09-17-2018, 10:23 AM
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good question.. I was assuming wheeldiameter not rim diameter because of him mentioning
it being a "scale model".. and with older cars and an assumed 2:1 scale replica
a 26" OD wheel isn't too absurd.. a 26" rim however would be

BUT again I was just assuming things.. so the scale might be different -say 1.5:1- and a 20" rim
is fairly common on 'more modern' vehicles than what I had in mind...

SOOOO the question is indeed worth to be answered,
especially since it'd throw off all my above calculations of course.

'sid
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Old 09-17-2018, 04:28 PM
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Yeah guys its 13" OD. Its a model of a Caterham (Lotus 7).

Sid, thanks for your input. Especially about the governor, thats good to know.
I mean, my butt is gonna be a few inches from the ground, so anything in the realm of 25 mph is probably gonna be way fast enough. More so off pavement.

Its probably gonna weigh a lot. It'll be big enough for 2 people, so I'm guessing it'll be heavier than 250 lbs dry.

I think I'll go for a 6:1 ratio, which at 5000 rpm is 32 mph. And if it works, but is beating up the clutch, maybe I'll try and reduce it a little more. If it doesn't work I'll just ditch it and get a nice TC.

If anyone would care, I could post the build process and design when I start
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Old 09-17-2018, 08:38 PM
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nono not 250 dry.. 250 all passengers seated

Soo two butts and a somewhat heavy kart.. 6:1 is NOT going to work!
let's just assume 660 lbs for a second (two 200lbs adults and a 260lbs vehicle)
you will need a 7.8:1 ratio to not burn your clutch.. and with that we're down to 25mph @5000 rpm again
plus that won't fit on your axle so you must use a jackshaft anyways..

if that jackshaft instead of a set of sprockets and a chain holds the tc you'll be golden;
really ditch that clutch entirely and replace it with a series 40 TC!

Why? simple.. a series 40 TC can give you the advantage you need.
anything lower than a 4.4:1 gearing will work (a 10T TC sprocket and a 44T axle)
resulting in a 44'ish mph top speed..

and if you gear more responsible 6:1 which still fits nicely you end up with 32mph
and a crap ton of torque propelling that hefty 660lbs vehicle up your local hill with barely any issues.

(something you'll surely be unable to do with a cent clutch)

'sid

PS please post your build process.. I'd love to see that come alive
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Old 09-17-2018, 11:51 PM
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I for one would love to see this build too. Who doesn't want to see a scale replica of a Lotus

And I agree with Sid...
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Old 09-18-2018, 10:35 AM
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Sid I meant 250 lbs without passengers. So yeah I agree, it’d end up weighing a lot.

I was afraid 6:1 wouldn’t work but had hopes. I’ll probably go ahead and build for the TC and buy it at some point along the build process. I got some other projects to finish up (don’t we all) then I’m gonna start building. Thanks for your inputs guys!

I’ll totally document it and post it here
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Old 09-18-2018, 06:41 PM
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Quote:
Originally Posted by itsid View Post
.....
on a lightweight kart ~250lbs or less (and weight is important!!)
a 5:1 ratio should work ....
Quote:
Originally Posted by bulby View Post
... so I'm guessing it'll be heavier than 250 lbs dry...
Quote:
Originally Posted by itsid View Post
nono not 250 dry.. 250 all passengers seated
...
Quote:
Originally Posted by bulby View Post
Sid I meant 250 lbs without passengers. So yeah I agree, itd end up weighing a lot. ..
I know what you meant, but I was referring to what I said above which you obviously misunderstood!
kartweight in oder to calculate a usable gear ratio is ALWAYS TOTALWEIGHT!

that's why I stressed out that my 250 lbs above is such totalweight.

'sid
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Old 09-18-2018, 06:41 PM
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Clutch this.
https://www.ebay.com/itm/40-Series-T...ry!60803!US!-1

Need to add a 3/4" Jackshaft if using the linked converter above.

Pillow block bearings can be found fairly cheap.
https://www.ebay.com/itm/2pcs-UCP-20...pe!60803!US!-1

A 3/4" keyed shaft.
https://www.ebay.com/itm/Keyed-Shaft...sAAOSwNchaCpjr

A handful of shaft collars.
https://www.ebay.com/itm/10-3-4-SHAF...ox!60803!US!-1

A 3/4" bore sprocket.
Need to find the correct number of teeth and correct chain pitch to work with the rear sprocket.
https://www.ebay.com/itm/10T-Tooth-4...MAAOSw9PNbmS7d

And a belt.
You need the jackshaft to be between 7-1/4" and 14-11/32" from the crankshaft.
The belt you need (based on the shaft spacing) can be found here...
https://www.bmikarts.com/PDF/Comet_40series.pdf

Or you can try something like this.
https://www.ebay.com/itm/Go-Kart-Tor...ry!60803!US!-1
The picture shows a sprocket, but doesn't mention if #35 or #41/#40/#420.
It also doesn't say how many teeth on the sprocket.

First option is probably a cheaper and better option, but requires more work.
Second option is probably a little more expensive and less reliable, but requires less work.
Looks like a stamped steel backplate. Not sure how durable those plates are.
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Old 09-18-2018, 07:42 PM
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Quote:
Originally Posted by itsid View Post
I know what you meant, but I was referring to what I said above which you obviously misunderstood!
kartweight in oder to calculate a usable gear ratio is ALWAYS TOTALWEIGHT!

that's why I stressed out that my 250 lbs above is such totalweight.

'sid
Ah ok my apologies Sid. I gotcha.

---------- Post added at 08:42 PM ---------- Previous post was at 08:36 PM ----------

bob, you are like an encyclopedia for parts links. I like that 40 series with the 3/4" driven. I suppose a 3/4" jackshaft is strong enough, and a 1" one would be overkill. I planned on doing 40/41/420 chain all around, with a 1" rear axle.

But hey, ain't no kill like overkill.
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Old 09-18-2018, 07:57 PM
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3/4" Jackshaft and 1" axle should be fine.
I'd get steel, not aluminum, for the axle.
Probably solid, not tubular.

I've got a 1.25" solid steel axle on my two seater but not sure if it overkill or not?
I've got a spidercarts granddaddy buggy.


So maybe a 10T #41/420 3/4 bore sprocket..
https://www.gopowersports.com/jacksh...hain-3-4-bore/

And a 48T #41/420 sprocket (and hub) for the axle.
https://www.amazon.com/Cart-Sprocket.../dp/B00QMSWOUI

Use #420 instead of #41 chain. It is much stronger.
https://www.ebay.com/itm/420-132-Lin...-/142921621816

And master links.
https://www.ebay.com/itm/10pc-420-Ch...lbcS7~&vxp=mtr


29mph at 3600 and 40 mph at 5k RPM.
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Old 09-18-2018, 08:52 PM
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More links! Awesome, thanks. Yeah I was looking at the solid 1", 44in long axle from Go Power Sports. Its got a keyway cut down the whole length of it.
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Old 09-18-2018, 08:55 PM
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gopowersports offers 10% off if you use coupon code DIYGOKARTS.
It might not work on everything they offer, but I use it on most stuff I get from there.
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Old 09-19-2018, 10:45 AM
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Also the code "red beard"

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