Go Kart Live Axle and Engine Conversion

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The Story

I got tired of my old kart single wheel drive spinning the tire and braking awkwardly, so I decided to convert to a live axle. At the same time I upgraded the engine and add a torque converter transmission. A big thanks to the guys over at diygokarts.com who helped me work through this project.

Engine Upgrade

When I got this go kart it had a small Briggs and Stratton engine on it. I'm not even sure if it was a 3.5 or 5 hp because it didn't have the flywheel cover on it. It would move around pretty good, but I wanted something that would burn out and haul 200 pounds of passengers up hill without hesitation. I also liked the idea of electric start. The clear choice was to upgrade to a 12.5 hp Kohler Commander lawn mower engine I've had laying around for a while.

Out with the old, in with the new

Frame Mods

Cuts, Welds, Gas Tank, and Engine Plate

First I test fit the new engine in the kart. With the torque converter attached it was a tight squeeze to get in and fit inside the existing cage with about a half inch to spare.

Test Fit

Since there was very little room inside the cage to move the engine around I had to position the engine mount plate based on where the engine fit inside the cage frame. Based on this I ended up having to cut a cross beam to make room for the engine mounting bolt to be screwed in. Since I had to cut one of my original cross beam re-enforcements installed, in preparation for the live axle swap, I decided to add some extra enforcement.

Cross Beam Cut

This engine also didn't have a gas tank attached like most go kart engines do. So I picked up an old tank from someone on Craigslist. I mounted it on some slotted plates held to the frame cage with some U-bolts.

Gas Tank

To secure the engine in place I had to make a new engine mount plate. I cut a rectangular plate big enough to hang out a couple inches on all four sides on the engine base. I laid it on the frame and put the engine in on top of it. Once I had it lined up where I wanted I marked the frame around the sides. This way I could line it back up if it moved when I pulled the engine back out. With the engine out of the way and the mounting plate lined up I welded it in place.

After the mounting plate was secure I put the engine back in place and marked the corners of the engine base on the plate. Then I held a piece of cardboard to the base of the engine and put the mounting bolts in to hold it in place. With the cardboard secure I cut it to the shape of the engine base. I lined the cut cardboard up with the markings on the mounting plate and marked the mounting holes to be drilled out. Instead of drilling in the center of the marked holes I drilled on the front and back edges of the marked circles so the engine could be slid forward or backwards to get the chain tight.

Finished Engine Mount Engine Mount Template

Controls

Throttle, Choke, and Ignition

With the new engine installed it was time to connect all the controls. I used a couple of Arnold Throttle Control Kits like the one below for the Throttle and Choke control.

I hooked one throttle cable to the existing gas pedal connection. fnaguitarplayer9 has a great video on how to install and adjust the throttle cable on the engine.

Throttle Adjustment


I added return springs to my throttle to make sure it would return to idle when I let off the gas.

I especially liked the universal throttle kit above for the choke control because it has a few different control levers to choose from.

Maybe my favorite thing about this engine, though, is the electric start. This means I don't have to mess around with pull starting the thing before I get in the kart. I just hop in turn the key and take off. I got the below key for my setup. It has all the connections I need and uses 3 positions: Off, On, and Start. While in the ON position there is a connection that would allow me to power up lights or other auxiliary connections.

Here's how I wired the basics up on my kart. Once everything was connected and working the way I wanted I wrapped the wires in split wire tubing.

Wiring Diagram Wiring

Axle Swap

I wanted to make sure that all power from the engine would be transferred to the wheels. I've had single wheel drive karts before and knew with this size engine I'd just spin the one wheel being driven. So I decided to convert the kart to a live axle that drives both wheels.

Frame Mods

Cuts and Welds While this kart didn't have a solid axle that spun both wheels it did have a square tube that ran through the middle of the frame with two short axles sticking out of either side. The short axles had to be cut off the sides to make room for the wheels on the new axle. Then I welded some square tube in a T at the end of the existing axle to mount the new bearing hangers.

File:ThunderBearingHangers.jpg
New Bearing Hangers

The bar across the middle of the frame also had to be cut to make room for the sprocket on the new axle.

File:ThunderSprocket.jpg
New Sprocket Location


Brakes

Relocation

Since my new, live axle was a little lower than the original one I had to re-position the brake connections. Since I was already modifying the axle area on the kart I decided to flip the brake band orientation and keep the brake peddle unmodified.

File:ThunderBrakeBand.jpg
Brake Band Mount

Hubs

Sprocket and Brake Drum

The brake drum and sprocket were originally attached to the drive wheel hub. The sprocket had to be moved towards the center of the card to match the new engine placement and the new wheel hubs I got didn't have a double ended hub for the brake drum to connect to. So I found some 1", Weasler Hub, X Series hubs at Tractor Supply. I could have ordered some hubs to fit the existing bolt patterns on the sprocket and brake drum, but the Weasler hubs were available the same day. The only problem was the hubs where just a bit larger than the center holes on the sprocket and brake drum. Luckily I figured out I could use a piece of bailing wire to squeeze in the gap to keep everything centered while welding the hubs in place.

Bailing Wire Hub Spacer X Series Weasler Hub

Wheels

Drill and Mount

Torque Converter

Mount

Plate

Drive Path

Backplate Mod and Jackshaft

Springs

More to Come!

Enjoy and feel free to report any problems or suggestions to longet@spider.dnsdojo.net.