scratch built almost done need drive ratio suggestions

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mbmopar

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hi all ,

firstly i'm going to be asking some questions that I kind of know the answers to but need clarification.

saying that, I'm almost done a home built go kart for my two kids 6 & 8 3/4. They are keen to get some driving in on it this fall before it gets really cold and or snows which could be a week from now ( read : Manitoba ).

IMG_2132.jpg

The frame is mostly free :thumbsup: based consisting of a scrapped snowmobile lift, trampoline frame and weight bench. The front steering is built with ackerman in mind and the "wheel" is an old plane yoke that was used years ago on a family friend's kart. bench seat is mounted on a dakota seat frame so it can adjust about a foot forward for the short lad, and back for the tall girl.

IMG_2131.jpg

IMG_2133.jpg

The rear tires are approx. 18" diameter, 60 tooth axle sprocket, 40 chain, 10 tooth clutch sprocket, 6.5 Powerfist engine (clone).

IMG_2138.jpg

I had it up in the air on the weekend ( jackstands ) and had one less link in the chain, it was too tight. so I removed the chain and resized the length. before reinstalling it I ran the engine and the clutch engaged slightly. like there was a slight drag on the drum. Being and new clutch, lubricated to mfg spec upon installation, i contacted Hilliard, they responded with some good info and suggested I install the drive chain and block the kart on the ground and fire it up. The chain stopped the premature slippage and things were looking up. at this point there was no signs of grabbing and overheating, the drum as quite cool to the touch after the engine had been shut down.

That was last night.

Today on my day off I tried to get the kart done for this coming Thanksgiving weekend so the kids could enjoy it.

I set all the cable tensions and went to drive the cart out of the garage. No go.

I'm a big guy, maybe too big, but it wouldn't move more than a few inches.

I came back in and read some threads and went back out side, rolled it onto the lawn and tried it again. The front lawn has a slight grade to wards the street. The kart moved ok straight down the grade under its own power but as the grade flattened and i turned the steering axle to give it a try the kart slowed right down......and the clutch got hot. Saw some smoke and the paint on the drum looks like my trailer fender when I overloaded it with limestone and the tire rubbed - hot and bubbly, see pic. I will say I think there may have been some oil from the bushing that may have slung under the drum as I saw some drips on the ground under the clutch. I will wait til it cools and see how slick it is inside as well.

I'm going to ask , I have a feeling I need to re-adjust the axle ratio:

A ) should I bother getting a 72 tooth sprocket or

B ) set up a jackshaft.

At this point I will have some finishing work to do, like floor extensions on each side, seat belts etc but and over anxious for the kids to have some fun. They are young and don't need a high speed machine, i would like them to get moving and have the push up some slight grades, etc.


if I am right looking at jack shafts, then the ten tooth engine / clutch to an 24 tooth j/s input, then a 20 tooth j/s output to the 60 tooth axle should give me 7.2:1 ratio.

do I need more ratio for the taller tires? suggestions on the ratio to shoot for if so. I used the Burris racing j/s calc.

Thank you all, I've learned alot so far on this site, and thanks for sharing your thoughts on this build.

Derek
PS - engine pics coming v soon
 
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firemanjim

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:welcome2:
Nice kart!great job! :wai:
To be honest with you, you really want a torque converter for that thing,but since you already have the new clutch.........
Jackshaft or big final sprocket...... The choice is really up to you, your driving area, and your wallet. You can drop to a 72 tooth or even 76,78..... It should work out just about right, for you... But in doing so, you rob yourself of ground clearance. If ground clearance is a major concern, then get a 50 tooth axle sprocket and the corresponding jackshaft sprockets to get to that ratio...... Gives you more ground clearance, still the same ratio...... :thumbsup:
It's all really up to the end user.....
 
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firemanjim said:
:welcome2:
Nice kart!great job! :wai:
To be honest with you, you really want a torque converter for that thing,but since you already have the new clutch.........
Jackshaft or big final sprocket...... The choice is really up to you, your driving area, and your wallet. You can drop to a 72 tooth or even 76,78..... It should work out just about right, for you... But in doing so, you rob yourself of ground clearance. If ground clearance is a major concern, then get a 50 tooth axle sprocket and the corresponding jackshaft sprockets to get to that ratio...... Gives you more ground clearance, still the same ratio...... :thumbsup:
It's all really up to the end user.....
Click to expand...

Thanks alot! I do know Ideally the t/c would be the right thing, but i'm trying to do this on the less expensive side for at least right now. I work at princess auto, where most of the items to build this were procured. I do have some 3/4" pillow blocks and some shaft at home so all Would need are a couple sprockets and hubs for now, the rest I could cobble up for a jackshaft and mount. saying that any idea what ratio I should shoot for?

gound clearance at this point seems ok, i could adjust to a 50 tooth axle sprocket and adjust the output on the j/s if need be.
 
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Bosch said:
This adds nothing to answer your question, but that's a good job on that kart!
Click to expand...


Thanks for the kind words, I would like to say that it is not quite done, but what build is? I

still have a nice checker plate trailer fender to cut up for four fenders, a chain guard ( nice curved sheet metal with holes punched into it - scavenged off a new wood chipper that was damaged in shipping. Also I'd like to better wire the cut out switch on the column, paint and add some roll bar type protection around the sides of the passengers from the back, i have some nice pre-bent material but have to tweak it so the seat travel will not be interfered with. And the crux is the cold weather is creeping in here....we usually have some snow by Oct 31

plus a few other doo dads to make it more fun for the kids, even the ones from down the street, who kept cycling past the garage on the night when I was staring to work on it....i told one kid we were building one and he screamed " I KNEW IT !" fun stuff !
 
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further to the drive ratio, I checked and we had all sorts of 40 chain sprockets in varying tooth count at work...this is not typical, when I and usually needing something the bin is most always empty.

So I set aside the 17 tooth and 24 tooth and hubs, this will give me the 8.47:1 number. I could throw a 16 tooth output on the jackshaft, this would give me 9:1....or a 15 tooth to get 9.6:1

would this be getting too high?

would this be more beneficial or stick with 8.5:1?

the cobbling will commence to tomorrow afternoon.

a co worker said he might have a short piece of 3/4" keyed shaft
if he does he said I could have it vs a new stick costing around 32 bucks. I thought I had some but don't
 
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mbmopar said:
further to the drive ratio, I checked and we had all sorts of 40 chain sprockets in varying tooth count at work...this is not typical, when I and usually needing something the bin is most always empty.

So I set aside the 17 tooth and 24 tooth and hubs, this will give me the 8.47:1 number. I could throw a 16 tooth output on the jackshaft, this would give me 9:1....or a 15 tooth to get 9.6:1

would this be getting too high?

would this be more beneficial or stick with 8.5:1?

the cobbling will commence to tomorrow afternoon.

a co worker said he might have a short piece of 3/4" keyed shaft
if he does he said I could have it vs a new stick costing around 32 bucks. I thought I had some but don't
Click to expand...

You have got it the wrong way around (your terminilogy). When you have a higher ratio number, it means you have geared LOWER. A low number means you are geared HIGHER

I would probably stock around the 9:1 area, as it is going to be your kids riding the kart and you don't want it to go too fast for them. You could always gear higher at a later stage for a bit more speed
 
firemanjim

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firemanjim said:
10-21-12-50=8.75:1...... Perfect.......
Click to expand...

landuse said:
You have got it the wrong way around (your terminilogy). When you have a higher ratio number, it means you have geared LOWER. A low number means you are geared HIGHER

I would probably stock around the 9:1 area, as it is going to be your kids riding the kart and you don't want it to go too fast for them. You could always gear higher at a later stage for a bit more speed
Click to expand...

I was thinking a happy medium of 8.75:1........ :lolgoku:
 
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