To make a go kart that corners on rails like a Porche, looks like a Ferrari and turns all your neighbor’s heads we need to back up the truck and go to the beginnings.
In short hand, there are five steps to making a simple frame. First of all the following steps are:
1. Engine And Passenger Layout
2. Drive Train System
3. Steering System
4. Brake System
5. Throttle System
Let’s get into it now….
1. Engine And Passenger Layout
First of all the assumption, whether this go-kart is made out of wood or is made out of steel is that you have some sort of layout in mind. Typically the engine is behind, and the person sits in front of the engine. A good safe layout is to have a seat protect the passenger from the engine.
So a structure of some sort is needed to hold the seat in place. You can use a seat off of a chair, but a more protective seat is a ½ piece of plywood angled back and supported. Covering the piece of wood is optional, but it is more comfortable with basically a piece of heavy cloth covering a cushion. The cloth is stapled typically into the board (on the backside).
The structure supporting the seat can be wood, or steel.
The frame work can be wood or steel as well. If using wood, use two by fours placed vertically, so that the strength of the wood is optimized.
If you are using steel for the frame, use a tubing that is at least .070 wall or thicker. The length of the frame is really dictated by how big the person is. Have a person sit comfortably in the leaned back position with a steering wheel in their hands. That is the person compartment. Measure this length.
Add the engine drive section and the person compartment lengths together and that is the length of the gokart. Cut your frame tubes (or tack tubes together) to this length. You will need at least two parallel lengths of tubing.
Space the tubes apart the width of the seat you made (20 inches is a good width).
Cut at least four (4) tubes to the 20 inch length. Lay all the pieces on the floor. Place the 20 inchers at the following locations: Engine Plate area, seat back section, seat forward section, front main bumper tube, and rear main bumper tube. (The bumper tubes can be wider than the frame by 12 inches (6 inches per side).)
Tack the tubes in place using a welder. If you do not have a welder, then you can fasten them together using plates and bolts. (Trust me, buy a $100 welder and save yourself wood chips and drill bits, busted knuckles and exasperation!)
What you have put together now is what I term a “flat-go kart.” You will soon find out that flat gokart frames are weak and require extra stiffening. You may want to put some struts into the system to bolster the frame design. Typically what I use is the seat back as reference. This works very well as an integral frame support, side seat holder, and engine protector.
2. Drive Train System
The next sequence is to place your engine and drive train system in place. At the same time put your seat in position to make sure the seat and engine are not hitting each other. Be sure to make the seat removable so that you can actually work on the engine system when needed.
When placing your engine typically a plate is needed to hold the engine onto the frame. Some designers use tubes with holes drilled in them for engine placement. I prefer the plate option, because it gives me greater options as far as engine choices in the future.
For example on the Phi-Alpha-10 and the Phi-Alpha-9 (go karts I designed) the engine plate served well in allowing me to use different engines, whether Briggs and Stratton, Tecumseh or even Honda. All engine types could be easily mounted just by drilling the holes in the motor mount plate.
Most go karts use a slot system to keep the chain tight. In other words, the engine is mounted not using holes but slots. That works, but honestly, drilling slots is intensive works and requires some patience and thought. So I prefer tensioning the chain, it works better on multiple fronts. (I can go on and on about engines, drive trains and such…but we have got to keep moving here…)
A word about drive systems: A live axle system is really the way to go. All you have to do is mount two bearing brackets and away you go. On a one wheel drive system, you need to have special rims that contain bearings, special drive sprockets that connect to the tires, and the axle if it gets bent, you have to cut it out of the frame and start over….so use a live axle…
But, that is not all true. You can get away with using old lawnmower wheels if they have bushings in them. They work great for acting as bearings. Grease snot out of the axel-hub interface and away you go. Be sure to retain the wheel with a cross bolt that is at least grade 5.
3. Steering System
So after having mounted the rear axle (with brake disc (or brake drum) and sprocket), and having placed the engine and chain system in place, proceed to mounting the front steering system.
Before we did some measurements of the person sitting in the comfortable position, make sure you remember the measurement (relative to the go kart frame) of the steering wheel. That is the target point for the steering wheel.
The actual position of the front wheels is a bit more involved though. You will need a scale. Place the scale first of all under the rear wheels. I typically use a board placed across the rear frame rails underneath the wheel area. Have someone sit in the go kart. (Be sure to a have the front wheels, steering wheel and steering structure on the go kart when you weigh it)
Now proceed to the front of the go kart and place the board in the general area that you want the steering system. Again weigh the go kart.
Take the two weights and add them together. That is the total weight. The front weight ideally should be with-in 5 to ten pounds of the rear weight. This is called 50/50 weight distribution. The more weight you have on the rear, the more the go kart will under-steer. Meaning, when you turn the wheel the go kart will tend to keep going straight. The more weight you have on the front wheels, the more the go kart will over steer. Most drivers are used to under-steer, it is easier to recover from.
But I digress…
Once you have placed the front wheels in place then fix the front steering system in place there. I typically use plates, so that I can move the steering system back or forward. So I weld mating plates on the frame and the steering system, then bolt them together.
For wood go karts, you can actually design a very stable wood go kart using the carriage style steering as long as the steering is supported an not aloud to twist.
A word on steering systems: You can purchase from the store steering assemblies that you tack onto tubes. These work real well, with one exception, they typically come in .750 inch diameter shafts, where most high speed bearings use .625 diameter shafts. The shafts may need replacement. Look for .625 shafts… Additionally, there are ways to make the steering more tractable and more user friendly, these involve geometric relationships such as camber, caster, Ackerman and so forth.
4. Brake System
Now that you have the steering system in position, you can button up the hole project by covering the bottom of the go kart. Sheet metal (like furnace guys use) is the best option. Buy some tech screws (the ones with drills on their ends) and zip through the sheet metal into the tubing. Once you have that in place, you don’t have to worry about your feet hitting the ground!
Now it is time to place the brake system. You notice we placed the brakes in place on the live axle, now the actual braking mechanism needs to be mounted to the frame work. You can either weld it, or bolt it to the frame. I prefer bolting, it is more forgiving and easier to repair.
A word on brake float: The brake system should float. What that means is that the disc either needs to be mounted freely on the shaft, or the brake caliper needs to float. If the neither is floating, you will get a binding, and prematurely worn out brakes, and fast! So keep that in mind. Something has to float, the disc or the brake caliper (1 of the 5!)
For your brakes it is important to have the brake off while driving. A good spring is needed to keep the pedal back when the brake is not being used.
On a wood go kart be sure to use the same thought into the brake system. A lot of force is going into the brake boards so be sure to account for this in the brake mechanism which usually involves force multiplier linkages.
5. Throttle System
This seems like the most inane or over looked system on the go kart. It shouldn’t be though. A good connection between the throttle and the pedal is needed and a good range of motion is needed too. Most pedals give you different holes to work with, allowing your several options in throttle actuation.
Again, like the brake, a good spring is needed. Do not use a spring on the carburetor, but use the spring in the pedal, or pedal system.
A word about throttles: most engines come with governors. It is a good idea to use the governor system, because it helps keep the engine at even speeds and from over revving.