First build Offroad kart/buggy

[tomas02]

Hi
Have been on here for a few months but thought it was about time i posted a build thread
Me and a friend from school are building an offroad kart for our school engineering project.
It has:
1987 Suzuki GF250SS motor
14" front wheels
16" back wheels (want to put these on front and get some 20-24" back wheels from a quad bike)
28.6mm live rear axle (inch and a eighth)
Rear swingarm suspension
Car bucket seat

Thats about all i can think of right now and questions ask and i will upload some pics shortly

 

[tomas02]

more pics

 

[redsox985]

That's gonna be one HE\\ of a ride! 250cc bike engine in there is gonna fly. It should be a lot of fun! Looking good. Make sure you get a nice harness for that seat.

 

[tomas02]

Yeah looking forward to getting this running to see what the engine can do haha.
Definitely going to find a harness. 4 point harness is minimum in my mind, not much point having a roll cage if you just smash your head on that lol

 

[tomas02]

took some more pics
can see size of wheels i would like on back of kart on right (is another class mates kart)
Have mounted my tacho now aswell dont have a pic of it.

Also could anyone tell me what sort of speeds i can expect from it know nothing of gear ratios.
13t drive sprocket
45t axle sprocket
atm 16" diameter wheels
Manual says:
- Primary reduction 2.285 (80/35)
- Final Reduction 3.789 (49/13)
Gear ratios
- 1st 3.083 (37/12)
- 2nd 2.200 (33/15)
- 3rd 1.722 (31/18)
- 4th 1.450 (29/20)
- 5th 1.315 (25/19)
- 6th 1.227 (27/22)
Also tacho says this can go to 17000rpm before red line

so if anyone could tell me what sort of speed this will do from that info it would be appreciated.

and if you need anymore info about it ask

 

[Gear box]

I know compared to mine, I have 14t on front and 60t on rear. This runs out little over 70 mph 72 73 some were in that range, this is with a 25x10x12" tires. I also have a EX500 Kaw motor pushing mine.

I would say on yours, this would run around 35mph to 45mph

 

[AceEngineer]

Speed Calculations

I assume the Final Reduction listed is the transmission output to rear wheel ratio of the bike the engine came out of. I cannot see a jackshaft in the pictures. You are replacing this with Your Final Ratio of 13/45 = 3.4615
If you still have the 49/13 drop in the drivetrain, you need to divide results below by 3.789
Gear box probably left this ratio in, explaining his results.

At Redline: 17000 RPM / Primary Ratio * 6th Gear Ratio * Your Final Ratio = Axle Speed in RPM

17000 / (80/25) * (27/22) * (45/13) = 1250.5 RPM axle speed

On each rotation of the axle you advance: Pi * 16 = 50.27 inches

In one minute you advance: 1250.5 RPM * 50.27 inches/ rev = 62862.6 inches/minute

62862.6 in/min = 5238.6 ft/min = 59.5 MPH in top gear at redline

FYI, running thru it again substituting 1st gear for 6th gear: = 23.7 MPH at redline in 1st

This sounds like a fairly good setup as the engine will have the horses to push all the way to the redline in top gear. Probably way less than where the bike topped out, which is a smaller aerodynamic load, so your kart will probably top out at redline. If you want to go faster, go up from the 13T and/or down with the 45T.

 

[tomas02]

Thanks heaps for the in depth answer.
not really wanting to go any faster than 60mph lol balls aint that big
but am wanting the low end torque. so hopefully this is geared about right but can always change axle sprocket easily if needed front one not so easy to change as its a sprocket i custom made to extend out so the chain could go down to the axle and clear the engine.
Really should of used a jackshaft in hindsight but oh well. we'll see how it goes

 

[tomas02]

so took it for a test drive last week but engine running like garbage.
vaccuum leak in carb boots and carbs need balancing
so its at motornike shop getting sorted
but here is video of first test run.

http://www.youtube.com/watch?v=1IdbraR8O48

P.S: ignore the tape holding the battery haha havnt got to battery mount yet, and really wanted to drive it.
Also this isn't me its my friend driving. I'm filming

 

[tomas02]

Just got it back from shop
they balanced carbs and fixed up mixture and a few other things.
It runs mint now heaps more power is alot of fun
heres a new video of a test run.
http://www.youtube.com/watch?v=-wZRgg7lLUE

 

[tomas02]

just got some rear quad bike wheels from a wreckers. 24x10-11 from memory.
going to put these on the back and put current back ones on front but think i'll probably need bigger fronts as well whats everyone think?
Current backs are 16x8-7

so will end up with 24x10-11 on back and 16x8-7 on front.
would this bog down engine at all?

 

[qtband]

How did you hook up the shifter and the clutch?

 

[tomas02]

Shifter is run by linkages made of 12mm rod, with a pivot point at the swingarm, so it doesnt shift when hitting bumps.
the clutch is a foot clutch and is run by cable

 

[qtband]

If you could add some pics of the linkage set-up, especially the pivot point, I'd appreciate it.

 

[JimmiH]

usefull info

very usefull information, thanks!

 

[tomas02]

If I can will do walkaround vid of it and show detail of shifter.
Very busy atm with school exams and fixing bent roll bar after i rolled it lol
wasnt planning on rolling before i put in the extra braces for rollbar but just had to drive it and got carried away

 

[tomas02]

Here is a video of the gear shifter linkages not great video quality and still need to tidy some of the welds up but you can see how each bit works.
http://www.youtube.com/watch?v=EfxBIxa5CNs

 

[wheels]

looks like it is moving pretty fast. good job. have you thought about putting bigger quad wheels on the front? might make it sit a bit higher though...

 

[tomas02]

Have thought about it. but at the moment im just trying to get the brakes finished, battery mounted and gearing changed so its ready for local christmas parade haha.

 

[kyjohn]

Cool, looks great !!!