The Pioneer class kart is the smallest of the sports racing cars. The working volume of its engine is only 50 cm 3 . Such karts are built for races in which children aged 9 to 16 years participate. Unfortunately, the industry does not yet produce these machines, and they are created in sections and circles.
Unlike “adult” karts, “Pioneer” has its own design features. Its frame, for example, is welded from thinner pipes and has a wedge-shaped shape. It is characterized by manufacturability and reliability. It has advantages over its own kind in rigidity and strength. By the way, we make this frame configuration for karts not only of the Pioneer class, but also of the Junior and Soyuzny classes.
The initial stage of construction is the development of drawings and preparation of fixtures and equipment. It is most convenient to draw the frame in full size on a sheet of graph paper glued to thick cardboard. Such a drawing will later serve as a template on which individual elements are roughly adjusted.
1 — front upper bump stop, 2 — gas pedal, 3 — brake pedal, 4 — gear shift lever, 5 — rear bump stop, 6 — brake disc, 7 — brake master cylinder, 8 — frame. A – steering column bearing, B – steering column thrust bearing.
It is necessary to draw the frame in two projections – top view and side view. Separately draw the front spar. Don’t be confused by the absence of some dimensions in the drawing – this means that the parts here need to be adjusted to the location.
The next stage is the manufacture of a slipway for assembling the frame. It will be required if you intend to produce these machines in a small series.
The base of the slipway is a sheet of duralumin measuring 1700X900 mm and 15-20 mm thick. A clear longitudinal line is drawn along its major axis – a trace of the plane of symmetry of the kart frame and perpendicular to it – the base line for installing the pin bushing clamps. The holes in the latter must be cut on a boring machine – this will ensure the necessary accuracy of installation of the bushings when welding the frame.
Steel corners are also installed on the slipway to secure the longitudinal spars.
1 — front lower bump stop, 2 — pedal axles, 3 — front cross member, 4 — pivot bushing, 5 — longitudinal member, 6 — floor mounting bracket, 7 — gear shift lever mounting bracket, 8 — gusset, 9 — front engine mount, 10 — rear support, 11 — rear axle bracket, 12 — rear cross member, 13 — main brake cylinder mounting bracket, 14 — brake lever axis, 15 — seat supports, 16 — middle cross member, 17 — steering column bracket, 18 — steering column support axis.
The frame itself is assembled from two longitudinal spars, three cross members (front, middle and rear), a front bumper and steering column mounting brackets. For its elements, it is preferable to use chromansil (made of 30KhGSA material) or seamless pipes made of grade 20 steel.
The order of their preparation for assembly is as follows. Cut the pipes with an allowance of about 30 mm and bend them using a tool according to the plaza drawing. This operation is best performed without heat. I propose several of the most rational methods for such processing.
The easiest way to bend pipes is to use a spring inserted inside from OBC grade wire. It is screwed on a lathe and then necessarily normalized. For thicker pipes you will need wire Ø 2.5-3 mm, and for the rest Ø 1.5-2 mm. The outer diameter of the spring should be such that it is inserted into the pipe with some force.
If the card frame is made in winter, then water can be frozen in the pipes before bending. Pouring molten rosin gives a good effect.
And finally, the traditional method of processing is stuffing with sifted and calcined sand. It is easier to bend the pipe by heating the bend with the flame of a torch or blowtorch. But this method is less preferable, since heating alloy steel significantly reduces its strength and elasticity.
1 – hub, 2 – axle, 3 – wheel rims (size in brackets – for the inner disk), 4 – bracket, 5 – kingpin, 6 – liner (2 pcs.), 7 – front cross beam, 8 – kingpin bushing, 9 – bipod.
Having given the blanks the required shape, adjust them – nail them to each other so that there are no gaps left in the joints. Start this work by installing the front cross member on the slipway (align the middle with the center line of the slipway). Next, install a clamp with a pivot bushing on one side and adjust the cross member to it so that the resulting plane is inclined at an angle of about 30° to the vertical. Perform the same operation on the opposite side of the slipway.
Press the front cross member prepared in this way with staples to the slipway and nail the longitudinal spars to it. Attach the rear cross member to the latter in a similar way, and the bump stop to the front cross member.
Fix all frame elements on the slipway with staples and clamps, check their position again and start welding. The best seams are obtained when using argon-arc or carbon dioxide welding, while conventional electric welding gives somewhat worse results. Gas should be used last.
Weld the frame in several stages. First, “tack” all the joints – each at one or two points, and then weld them completely. Without removing the frame from the slipway, weld the engine and rear axle mounting brackets. Pre-install the latter on the axle – this will help ensure that it is perpendicular to the plane of symmetry of the frame.
on the left is the front, on the right is the back.
The pedal axles, steering column brackets, middle cross member and seat supports should be welded only after preliminary “fitting” of the kart to the racer. The lower part of the seat is located at the same level as the lowest points of the frame side members. The correct rider’s position has the following characteristics: the back is tilted back 20-25°, the legs are slightly bent at the knees.
The last to be welded are the floor mounting ears, the brackets and tubes of the front upper bumper, the gussets at the junction of the longitudinal side members with the front cross member and the gear shift lever ears, as well as the cable stops.
For the front axle you will need several turned parts, in particular front hubs (from D16T), axles (from 30KhGSA), bronze bushings and king pins made from steel 45 or 40X.
It is best to bend the eye of the front axle from a steel strip measuring 40X30 mm according to a template. A lever, a reinforcing gusset and, last but not least, a trunnion should be welded to it.
1 – front, 2 – rear, 3 – elements for attaching the rear bumper to the frame.
The design of the rear axle is quite simple and technologically advanced. The bearing housing hubs are cast from aluminum alloy with subsequent finishing on lathes and milling machines.
The brake card is a disc brake with a hydraulic drive. According to the technical specifications, Pioneer class karts are equipped only with rear wheel brakes.
The brake disc is mounted on the rear axle of the kart, and the brake machine is installed on the frame. Its body is made of duralumin, the working cylinder is steel (30KhGSA or Art. 45). The piston is made of brass or made of D16T material.
You can also use the front shoe brake from the T-200 scooter or M-106 motorcycle. When installing it, you should be very careful about the alignment of the brake drum.
1 – wheel hub, 2 – brake disc, 3 – brake disc hub, 4 – axle support bracket, 5 – shaft, 6 – wheel disks, 7 – sprocket, 8 – sprocket hub, 9 – bearing housing, 10 – brake unit.
To select the optimal gear ratio of the rear axle chain drive, it is recommended to manufacture a set of driven sprockets with a number of teeth from 22 to 28 with an interval of two teeth. This will greatly facilitate the adjustment of the drive to the weight of the kart and rider, the engine power and the speed of its drive sprocket.
The kart wheel rims can be made from aluminum alloys D16AM or AMG-6. The thickness of the workpiece sheet is 2-3 mm. The method for extruding a disk is as follows. First, a punch is turned from any metal. The workpiece is pressed against it by the tailstock of the lathe and rolled by a roller fixed in the tool holder until it takes the shape of a punch. Processing is carried out at a rotation speed of the machine chuck from 150 to 300 rpm, and ordinary soap is used as a lubricant.
It is best to drill holes in wheel rims using a jig template. It is advisable to make the latter from steel and harden it. Take the time to do this, especially if you are planning to build several cars.
The fastenings of the front wheels, steering rods and pedals must be pinned; Self-locking nuts are also quite acceptable.
As already mentioned, on Pioneer class cards it is allowed to install engines with a cylinder capacity of up to 50 cm 3 , in particular, domestic engines Sh-51, Sh-52, Sh-57, Sh-58 and Sh-62. You should not immediately start boosting the engine – this will sharply reduce its service life and reliability. You just need to adjust the carburetor and ignition correctly. For starters, this will be enough for you.
For the gas tank, it is best to use a 2 liter polyethylene canister. It should be placed on the sled so that the fuel flows by gravity into the carburetor. A fitting or tap is inserted into the bottom of the container, and a hole is drilled in the plug of the canister through which a polyvinyl chloride tube is passed.
The tension of the engine chain is regulated by a stop – a tander with two ShS-8 bearings pressed into its ears. If such a tander is not at hand, weld an M10 nut onto the frame and screw a bolt into it so that it rests against the engine mounting bracket.
The chain is covered from above with a plastic shield, half blocking the driven sprocket. Shield width 30 mm.
The steering column is installed at the distance of the athlete’s outstretched arm (the hand grips the upper part of the steering wheel). This is a steel pipe Ø 18 mm; in the lower part a rotating bipod is welded to it – a lever made of a steel strip about 2 mm thick. When cutting a hole in the bipod for the tie rod, remember that the optimal ratio of the lengths of the front wheel steering knuckle arm and the bipod arm is 1.7:1.
Steering rods are tubular; bushings with ShS-6 or ShS-8 bearings are tucked into their ends, or, in extreme cases, rubber bushings. After assembly, check the functioning of the steering mechanisms: the axle should rotate at an angle of about 35°. If the angle of rotation is greater, make stops.
The steering wheel is cold bent from an AMG or AMC pipe with an outer Ø of 22–25 mm and a wall thickness of 1.5–2 mm. The pipe is filled with sand and wound in several turns onto a suitable mandrel, for example, a gas cylinder. In this way, blanks are obtained for several “steering wheels” at once. The spokes are cut from 4-5 mm aluminum sheet of the AMG or AMC brand. I warn you that making spokes from “hard” alloys D16T, D19T, V95 and the like is not recommended – cracks may form at the welding points and the steering wheel will fall apart. Then the steering wheel is attached with three bolts to the steering column thrust pad, sheathed in leather or leatherette with preliminary pasting of microporous rubber or foam rubber.
1 — caliper, 2 — spring, 3 — lining fastening screw, 4 — brake cylinder, 5 — hole for bleeding the cylinder, 6 — rubber cuff, 7 — piston, 8 — brake lining, 9 — friction plates.
The brake, gas and clutch pedals are curved from steel pipes Ø 12×1.5 mm. The rings for which the cables are attached to them, as well as the stops, are connected to the pedals by welding. When assembling, do not forget to install a return spring on the gas pedal.
The floor is made of duralumin sheet 1.5 mm thick; it is attached with screws to lugs welded to the frame.
The easiest way to glue a seat out of fiberglass is to use a map of the Leningrad DOSAAF plant as a “boob.” When gluing the obrlochmi, apply a separating layer of parquet mastic to the “boob.” It is advisable to paint the seat not after gluing, but immediately by mixing black pigment into the epoxy resin.
The seat is attached at the front to brackets welded to the kart frame, and at the rear to two adjustable tubular supports.
After control assembly, debugging and adjustment of all mechanisms, the machine must be completely disassembled. Thoroughly clean the frame from rust and scale, degrease, prime and paint with nitro or synthetic enamel. It is advisable to chrome the bump stops, steering column, pedals, tie rods and gear shift lever. The steering knuckles of the front wheels can be painted black.
Cut out the card numbers from plastic, their dimensions are 220×220 mm. The corners of the square should be rounded with a radius of 20 mm.
K. KRUGLIKOV, head of the karting club
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