Other Homemade Gokart
* This page has been reproduced with permission from the original publisher for your enjoyment. *
Please do not email me about this kart.
Click on any image to see a larger version.
Drawings for Phase I
This is my first try at a ground up design for an offroadvehicle. It will be fully suspended with equal length A-arms in front andswing arm rear suspension. The front shocks are cheap ATV shocks ($13 ea.)with 2" of travel and 260lb/in spring rate. By connecting them about halfway out on the bottom A-arm, I get about 5" of travel at the wheel. Thesteering hub will be a king pin design.
For power I'll probably use a 5hp Briggs and Straton engine.There are plenty of aftermarket parts to make these engines produce morehorsepower and achieve higher rpms. Further down the road I'll try my handat creating an electronic fuel injection system for this motor. The enginewill drive the solid 1 inch live axle using chain and sprocket.
Braking will be accomplished with a single disk mountedon the live axle for now, in the future I hope the find a wrecked quadand used the disk brake front hubs to provide front brakes.
The frame is constructed of 1/16" wall 1" sqaure mildsteel tubing. I'm using square tubing for ease of construction and to limitthe number of new tools I need to buy.
My biggest challenge in designing the steering systemon a suspended vehicle is eliminating the bump steer problem i.e. changesin toe angle as the suspension moves through it's travel. The trick isto make the steering linkages follow the same path as one of the suspensionlinkages. The image below shows the system I ended up with. The steeringwheel is connected to a 'linear actuator' via chain and sprocket. The sprocketon the steering column can be changed to achieve different steering ratios.The sliding rod (linear actuator) acts much like a rack and pinion andconnects to the tie rods and about the same point where the lower A-armconnects to the frame. The tie rod follows the same path as the lower A-armsuch that there is no change in length i.e. no bump steer as the suspensionmoves through it's travel.
It's finally done!
Here are some cool shots of the completed kart. I'm verypleased with the final product. I've driven it mostly on gravel roads whereit handles very predictably with slight catchable oversteer. Top speedis about 40mph as predicted. The clutch is a standard centrifugal clutchand slips a little on start up i.e. take off must be on level ground. Thebiggest impression when first driving the kart is how amazingly stableit feels, it seems like it would be impossible to roll it.
Specifications and Features
- Fits in the back of a Toyota truck 4.5' X 6'
- race prepared 5hp B&S block making about 8hp
- hydraulic disk brake with cross drilled rotor on rear axle
- kill switch
- 8" ground clearance
- 18 X 9.5 rear tires
- 15 X 6 front tires
- double A arm front suspension with 5" of wheel travel
- swing arm rear suspension with 5" of wheel travel
- flag mount
- 40mph top speed
Phase III - bigger motor
After trying a number of different clutches to improveinitial acceleration, I came to the conclusion that a centrifugal clutchjust wasn't going to work. The next best alternative was to mount a beltdriven torque converter but that would require a complete redesign of therear end. Fortunately, about this time I came across a good deal on a partedout '87 CR125 dirt bike. The motor is water cooled and puts out about 30hpcompared to 8hp from the Briggs motor!
With a bit of remorse I pulled out the die grinder andstarted pulling apart the rear end to accomodate the new motor. At thispoint, I have the motor and exhaust mounted, and the motor running.
This version of the kart also has a much better seat anda 5point harness .
Well it's been awhile but I finally finished phase III.The new motor is in, plumbed, wired, and ready to run. For the first testI took it to a gravel lot to try it out. I was completely unprepared forhow much power and torque this motor had. Within 5 minutes I had bent severalkey supports such that the chain and exhaust kept falling off - back tothe drawing boad. A few hours bending stuff back into place and weldingmore braces in and the kart was ready to go again. This time it run flawlessly.The kart is just unbelievably fast with this motor, and a lot more funto operate too. The big problem now is to keep from spinning the tires:-) Quite a big change from the last motor where I needed a push startto get the centrifugal clutch engaged!
Where can I get the $13 shocks?
I purchased the shocks and a few other components from Northern Hydraulic. You can request a catalog online. Keep in mind that these low end shocks are really just springs, they containno damping capability. For low speed (<20mph) this makes for avery comfortable ride but if you want higher speed and higher performance,I would recommend using a motorcycle shock with adjustable damping anda choice of spring rates.
What are some other internet karting sites?
Rieken's Racing has a really completeonline catalog and good service
Northern Hydraulic hasa small selection of really cheap kart parts
How did you get more horsepower out of the 5hp engine?
First off, I didn't do this work myself, I had it done by a local 4-strokekart racer. He did this stuff as a side business and had lots ofexperience. These are the basic things that he did to my engine.
On his engine dyno, my engine produced 7.5-8 hp at 5000rpm
- remove some material (0.01-0.02") from the gasket surface on the head soas to decrease the final cyclinder volume and increase the compression.
- bore out the carberator tube to 0.75" for better flow.
- install a tuned header exhaust.
- new piston and rings
- 3 angle valve grind
Where can I get drawings for your kart?
The only drawings I have are here
Can you take more/better pictures of your kart, steering system, etc?
No, I sold this kart a while ago so I no longer have access to it to take more pictures
Can you provide better drawings, pictures, or descriptions of the steering system?
I get a lot of questions about the steering system. I used this system because I had all the parts in the garage so it was basically free to me. I guess there must be a lot of people in the same boat because I find if very surprising that people would want to use it. In other words, if I had my choice of components for the steering, I would MUCH rather have a real rack and pinion as it would be a lot sturdier than the chain drive system.
Having said that, here is my best description of the chain drive steering system. It's based on a similar principle as the rack and pinion except instead of a gear drive, the rack is actuated by the chain directly pulling on it. The rackconsists of a straight rod that passes through the frame on bushings, the tie rods connect to each end of the rack.The chain is driven by a pulley on the steering shaft. The chain goes straight down to another set (2) pulleys thatredirect the pull force from vertical to horizontal (parallel to the rack). Each end of the chain is then attachedto the rack so that when the steering wheel is turned, that force is transmitted through the chain to pull the rackback and forth and eventually move the front wheels.
Hopefully this helps, if you still don't get it, examine the pictures at the top of this page carefully, they actuallyshow pretty good detail of the steering.
What kind of welder did you use?
I used a Lincoln Weldpack 100 wire feed electric welder. I used flux core 0.032" wire with no shield gas. This system is very cheap ($350) and works quite well. The downside is that a lot of time is required to cleanup the welds with a wire brush when you're done. If I could've afforded a MIG welder at the time, that would'vebeen much preferred.
Last update 10/24/98