Kid's Pedal Car converted to a two-stroke powered Pedal Kart

Hello,

Relatively new member here, but actually a long time reader of Auto-X, wait I mean Grassroots Motorsports. Gen-Xer...grew up around cars with my dad in Austin, TX. We built a Beck 550 Spyder in the mid '80's that we started autocrossing with the Texas Spokes. I autocrossed in high school the same year I got my driver's license.

Later, while in the process of getting a mechanical engineering degree, I participated in Formula SAE. After graduation, now gainfully employed with some disposable income, I went go kart racing. In 10 years of karting, i progressed from 100cc clutch karts at the club level to roadracing 125cc shifter karts, and ultimately 250cc superkarts....the absolute best bang for the buck in racing.

Meanwhile, marriage and kids happened. Karts are sold. Life slows to a sedate family pace. Two wonderful boys. But my time and energies are continuously torn between family and work. One day 10 years later, some time last year, I noticed a derelict child's pedal car propped up against the brickwork along side my neighbor's house. It was a pretty fancy little pedal car that had a steel tube frame, and fancy wheels and accessories. After looking at the thing sitting there for months every time I late-apexed the riding mower around the tree at the edge of our property, I asked him about it. Turns out his 7 year old grandson had out grown it and, "the steering was broken" Hmmm...I wonder if I could motorize it....

Pretty cool little car:

Next day it was ours and in the garage....

My thought process was to motorize it. Turn it into a small go-kart. Possibly using one of the 25cc two stroke weed eater engines I keep in inventory for just such an occasion. (The only acceptable power for a go-kart unit is a two stroke). Unfortunately, the weed eater engines are....not well suited for this application. It's a structural issue with the crankshaft. And weed eaters don’t use chain drives. My original thought was to graft on a weedwacker motor on the back and cobble up some sort of a brake. However, after looking at the donor Ryobi trimmer motor, and the room behind the seat (which is adjustable), there wasn't going to be much room put a motor.

Several weeks go by. Meanwhile, the aluminum can bin in the shop is full (a dad’s work is never done) so the boys crush the cans and we take it to the local metal scrapyard to recycle the cans. The boys always enjoy this, because they split the cash "take". The curmudgeons who run the scrap yard have taken a liking to my sons. I take them there to teach them the value of recycling, and also for the chance to interact with hard working folks who sling rusty metal around for a living. While in the scrapyard, I spy a discarded Chinese pocket bike….an old mini-bike…consisting of wheels, a frame, the remains of a motor, chain, and disc brake. The motor isn’t seized, and it sure looks like an interesting little (two-stroke) power unit. So I roll it over to the scale and we buy it….for scrap price….$12.

I wish I had a better photo of the scrap bike and engine, but I was too excited!

Turns out this is the perfect donor motor for our project! A 47cc air cooled reed valve two stroke engine! The motor needs a lot of work. It’s missing a ton of parts. However some quick research on Ebay confirms that there is an abundance of parts for these little motors. Plus it looks like it might fit under the seat! The engine turned out to be in remarkably usable condition, it just required a new starter shroud and exhaust, and a few other bits and pieces….all sourced via ebay thru Chinese suppliers. This was a total game changer….the pocket bike engine is lower profile, designed for a chain drive, and easier to mount. The lower profile of the engine allowed me to install it underneath the existing seat.

Mocking up the $12 scrapyard motor. This was the condition of the engine after I removed it from the minibike frame:

Side View of the engine:

This looks like a very dangerous toy for your young children. You're a cool dad.

In reply to conesare2seconds:

Thanks. My gearing calculations say it will go about 20mph. They go faster on their bikes down the hill. My sons are 10 and 8. A primary purpose of this project is for father/son learning experiences.

I can tell you're gonna be a dangerous addition to this forum.

WELCOME ABOARD!!!

This is awesome.

See, thats the problem with this place. I had conveniently forgotten about the go cart project i have in the shed, as my daughter was "too young " shes 8 now....

Damn it. Gonna have to finally finish it ...

Kart wheels and tires I hope?

I say keep the plastic wheels for a while, Way more fun getting sideways.

Also these chinese pocket bike motors have an entire aftermarket around them. So these kids can do their own upgrades and go faster. Get them hooked on speed parts early

We're doing a "spiral development" plan:

1. figure out how to get motor installed
2. make all the drive train parts
3. rebuild motor
4. figure out pedals
5. floor pans
6. controls
7. upgrade steering
8. upgrade wheels

TeamFAST wrote: We're doing a "spiral development" plan: 1. figure out how to get motor installed 2. make all the drive train parts 3. rebuild motor 4. figure out pedals 5. floor pans 6. controls 7. upgrade steering 8. upgrade wheels

Otherwise known as Mission Creep

The Pedal Kart plan is centered around the new donor engine. Fabricate a mount underneath the seat, build a rear (live) axle incorporating the minibike brake rotor and rear sprocket, with hubs to attach the stock plastic rear wheels. Pedals and floor pans would be required too. Plus some sort of a gas tank, and a few frame mods.

There are TONS of parts for these engines at ridiculously cheap prices (if you are willing to wait the 2 to 3 weeks for China shipping) so i ordered the parts needed to make the engine whole again. Amazingly the piston and cylinder are in excellent condition (and Nikasil plated) so I re-used them. Doesn't look too bad for a $12 junkyard find!

Here's a view of the motor mount, mocked up from aluminum flat bar. Plan is to cut out the motor mount plate from the minibike frame, and incorporate it. The mount will be slotted where it bolts to the frame to allow me to slide it forward to tension the chain.

The rear cross member and those curved bumper support tubes are going to have to go...

I see treadless sidewalls only rear meats in your future. That bullet looks alarming like my Stihl 036...

Machining some rear hubs. The scrap pocket bike donated a caliper and a disc brake (seen in the previous photos).

Believe it or not, I made sense to run the stock rubber capped plastic wheels. At least initially. Until they wear out. These hubs are designed to use the plastic wheels and a 1/2" axle. Same diameter as the stock axle.

shown with keyway broached:

Next up: Sprocket and brake disc hubs

Picture of the broaching process ?

Broaching process:

This is the rear sprocket hub. To make the keyways I used a standard Dumont style 3/16" broach and bushing pressed through with an arbor press.

Here's the two wheel hubs, the sprocket hub, and the brake disc hub after machining on the lathe and broaching:

The parts took three setups: lathe and two mill setups. Decided to add fancy lightning features...because pedal kart! This was over the winter break. Santa Claus brought us a new rotary table for the Bridgeport. Gotta love free shipping!

Mill setup:

I had to make some significant frame mods to accommodate the sprocket and brake disc. I cut out the rear cross member and bumper support tubes. Then I TIG welded some new supports from some leftover 4130 tubing i had. For the time being I am using the original plastic axle bushings and supports. It will be interesting to see how long they last!

New bumper supports. Designed to act as a saddle to support the bumper to allow it to remain removable.

Welded onto the frame. I took a page from Mazdeuce's book and got some quality shop time in while the boys were at school.

Rear axle test fit with all the new machined parts:

TFast, thanks for the broach shot, excellent choice on cordless drill...have two myself. What is the model # on the Bridgeport? Looking GOOD!

My mill is a Bridgeport Clone. It is a Comet....mid 80's Taiwanese. Good quality castings, one of the better clones. Would have liked a real Bridgeport but this one was available and the price was right. It does have a two speed 3 phase motor which is nice.

Wow - fantastic fab work.

My oldest son was 9 at the time we started this project. When I started welding the bits and pieces to the frame, he was fascinated by the welding process. Fire! Heat! Sparks! He was curious enough that I introduced him to TIG welding and the concept of the electrical arc melting the steel. I taught him how to hold the torch to create a puddle and move it along the metal to form a bead. He's a natural! He really seems to enjoy welding. I let him try stick welding on our pipe fence a few months later. To me this is the coolest aspect of projects like this...introducing my sons to the shop. Much better than video games.

I ran the pedal for him. All he had to do was maintain proper distance and move the torch along the piece of angle iron. I tried to simplify things for him.

Results. I am jealous! I didn't learn to weld until college! Practice makes perfect...

Dang, I still cant even weld to save my life! This is awesome