A brief introduction/info-session before my question
I'm building a Kart for my two boys aged 7+4 y/o. I'm rolling with what comes to me cheap / free. As of now I have a free '76 T'NT 340 Sled with a 339.2 cc 345 series Rotax twin (probably about 30HP) Free Air Motor (which I will be employing despite the hoopla regarding over-heating in the summer). It was seized with no spark - but after $6.50 in parts - runs like a champ. I also have two free Lawn tractors 1 a 12HP Craftsman, and one 17.5hp Yardworks (Intek motor).
The plan is to take the engine, steering, throttle control, brakes, clutch, seat materials, misc sheetmetal, + wiring harness off the sled.
The rims and tires will be from the 12hp Craftsman (17.5" dia rear, 13" dia front), I may take the front axle, gas tank, misc steering components, rear fenders, steering wheel, and a couple idler pulleys off as well just in case I might have a use for them.
I will be taking the horn, one head light, steering wheel ('82GT yo!), one caliper, one disk, and whatever else seems to have a possible Kart use from a resident Mustang which is awaiting higher scrap prices
.
I have a very nice master cylinder from an '05 PT Cruiser GT which was gratis.
So I have a nice collection of parts for no cost at this point. I'm a steel buyer for a living so the frame of the Kart will be fabbed from steel purchased at the same unit cost a large Fabricator would pay.
Today I priced out the pillow blocks, flange bearings, 2 pc shaft collars, sprockets and chain from one of my suppliers - and here I am looking at some real dollars:
2 pcs 40B12's 1" finished bore (Martin Gear)
2 pcs 40B35's 5/8" RS bore (Martin Gear)
4 pcs 1" EBC pillow blocks (made in China)
2 pcs 1" EBC 4 blt flange bearings (made in China)
6 pcs 1" 2 pc shaft collars (who cares)
1 box 10' of #40 chain (Tsubaki)
This would run me about $180.00 - which is not too bad - but I'm so far at zero cost - I want to keep the ball rolling.
To eliminate the jack shaft (and save a good chunk of the above cost) I'm thinking of eliminating the driven sled clutch and replacing it with a fixed pulley. The stock set up gives me approximately a 1.433:1 ratio before the secondary opens up, and after the primary squeezes shut (7.5" dia max on driver, 10.75 before opening on driven) but of course in reality both move simultaniously for a good part of the rev range. With a fixed pulley, I could squeeze in a 12" dia pc in there - giving me 1.6:1; and at 8000 engine rpm, I would be looking at 5000 rpm maximum at the fixed pulley. I want an 800 RPM axle speed with my 17" dia wheels to give me about 65 KPH minimum (engine might do more than 8000...) so I would need a 6.25:1 step down in one shot to the axle from the fixed pulley. I can get close with a 40B12 + 40B72 allowing 6:1 for a 833 rpm shaft speed and roughly 67 KPH minimum top speed and should allow great low end grunt. The stock clutch assy gives approx 1.2 overdrive at max rpm (rough measurements of diameters), about 4:1 step down in the chaincase and 10" belt sprockets giving an overall "wheel" speed of 6280 fet per minute. This should have allowed the sled to do about 114 KPH roughly. My arangement with the fixed pulley has a wheel speed of only 3707
feet per minute - almost doubling the gear reduction in the system. With this arrangement I could heave the entire jack-shaft and everything related to it - and save the cost and time required to put it in.
It sounds good on e-paper - has any one tried something like this?
Please critique the above at your leisure.
If you have something to add - please don't hesitate!
I'm almost ready to start building, and I'd like to know now rather than later if there is a cheaper/better way to arrange the powertrain. The above is about as cheap as I could come up with while maintaining the requirements I had originally laid out (and don't want to change).
I'm building a Kart for my two boys aged 7+4 y/o. I'm rolling with what comes to me cheap / free. As of now I have a free '76 T'NT 340 Sled with a 339.2 cc 345 series Rotax twin (probably about 30HP) Free Air Motor (which I will be employing despite the hoopla regarding over-heating in the summer). It was seized with no spark - but after $6.50 in parts - runs like a champ. I also have two free Lawn tractors 1 a 12HP Craftsman, and one 17.5hp Yardworks (Intek motor).
The plan is to take the engine, steering, throttle control, brakes, clutch, seat materials, misc sheetmetal, + wiring harness off the sled.
The rims and tires will be from the 12hp Craftsman (17.5" dia rear, 13" dia front), I may take the front axle, gas tank, misc steering components, rear fenders, steering wheel, and a couple idler pulleys off as well just in case I might have a use for them.
I will be taking the horn, one head light, steering wheel ('82GT yo!), one caliper, one disk, and whatever else seems to have a possible Kart use from a resident Mustang which is awaiting higher scrap prices
.I have a very nice master cylinder from an '05 PT Cruiser GT which was gratis.
So I have a nice collection of parts for no cost at this point. I'm a steel buyer for a living so the frame of the Kart will be fabbed from steel purchased at the same unit cost a large Fabricator would pay.
Today I priced out the pillow blocks, flange bearings, 2 pc shaft collars, sprockets and chain from one of my suppliers - and here I am looking at some real dollars:
2 pcs 40B12's 1" finished bore (Martin Gear)
2 pcs 40B35's 5/8" RS bore (Martin Gear)
4 pcs 1" EBC pillow blocks (made in China)
2 pcs 1" EBC 4 blt flange bearings (made in China)
6 pcs 1" 2 pc shaft collars (who cares)
1 box 10' of #40 chain (Tsubaki)
This would run me about $180.00 - which is not too bad - but I'm so far at zero cost - I want to keep the ball rolling.
To eliminate the jack shaft (and save a good chunk of the above cost) I'm thinking of eliminating the driven sled clutch and replacing it with a fixed pulley. The stock set up gives me approximately a 1.433:1 ratio before the secondary opens up, and after the primary squeezes shut (7.5" dia max on driver, 10.75 before opening on driven) but of course in reality both move simultaniously for a good part of the rev range. With a fixed pulley, I could squeeze in a 12" dia pc in there - giving me 1.6:1; and at 8000 engine rpm, I would be looking at 5000 rpm maximum at the fixed pulley. I want an 800 RPM axle speed with my 17" dia wheels to give me about 65 KPH minimum (engine might do more than 8000...) so I would need a 6.25:1 step down in one shot to the axle from the fixed pulley. I can get close with a 40B12 + 40B72 allowing 6:1 for a 833 rpm shaft speed and roughly 67 KPH minimum top speed and should allow great low end grunt. The stock clutch assy gives approx 1.2 overdrive at max rpm (rough measurements of diameters), about 4:1 step down in the chaincase and 10" belt sprockets giving an overall "wheel" speed of 6280 fet per minute. This should have allowed the sled to do about 114 KPH roughly. My arangement with the fixed pulley has a wheel speed of only 3707
feet per minute - almost doubling the gear reduction in the system. With this arrangement I could heave the entire jack-shaft and everything related to it - and save the cost and time required to put it in.
It sounds good on e-paper - has any one tried something like this?
Please critique the above at your leisure.
If you have something to add - please don't hesitate!
I'm almost ready to start building, and I'd like to know now rather than later if there is a cheaper/better way to arrange the powertrain. The above is about as cheap as I could come up with while maintaining the requirements I had originally laid out (and don't want to change).
