DIY Go-kart Build

Engine Stripdown
Engine Rebuild
23 December 2018
When I was eight or ten years old, my uncle offered a go-kart with a motorbike engine to me that my cousin, his son, had built. As a naive child, I thought I was getting a fully working go-kart and couldn't contain my excitement. My father tried to warn me that it wasn't working, but of course I didn't listen. When we went to my uncle's house with a trailer to collect the go-kart, I was disappointed to find that it was just a frame, a seat and an old engine (the seat and engine weren't even attached to the frame).
My father bought four wheelbarrow wheels for me and attached them to the frame so my friends and I could push each other around on it. I got years of fun out of that until, in my mid teens, I decided to start working towards installing the engine in it.
When I started looking for ancillary parts for the engine (which was from a Honda CD175), I soon realised that it was from a classic bike and it would be difficult and expensive to restore. I saved some money and, with some financial help from my parents, bought a fully working motorbike engine from a local motorbike shop. I knew nothing about motorbikes at the time and the engine I bought was one that the bike shop had removed from a crashed Suzuki RG125 Gamma.
I had to completely redesign the rear of the frame to suit the new engine. The design evolved from the materials I happened to have because I couldn't afford to buy the steel and other parts for a bespoke design. The photo below shows the first version of the go-kart, where I used the frame of an old chair to mount the fuel tank and radiator above the engine.

Go-kart Autumn 2002

I made improvements to the design over time, including adding a stronger roll bar to which the radiator, fuel tank and lights were mounted. The RG125 Gamma engine has an exhaust value but the control wires were cut right back at the solenoid housing. I soldered new wires to it and wired it to a push button on the steering wheel. I used the push button like a NOS button and with some experimentation learnt to tell by the sound of the engine where in the rev range to hit the button. The fastest speed I got from the go-kart was 82kph, uphill on a private road to a reservoir. I could get up to 50kph freewheeling downhill from a standstill at the top, so often speculated that I could have gotten as much as 130kph out of it on the flat - although I would never have trusted my own welding at those speeds.
Below are photos of the go-kart in August 2005, which show it in its prime.

Go-kart on Bonfire Night (23rd of June) 2005

I finished my degree in June 2005 and started working full-time the following October. Unfortunately, the go-kart was neglected from then on and soon fell into disrepair due to being stored outside. I did, at some stage, have the sense to remove the carburettor and store it indoors. This was the sorry state of it, 13 years later, in July 2018:

I had always planned to get the go-kart up and running again but I recently realised that it's beyond the point of repair and requires a complete rebuild. Parts of the frame are over 30 years old and it wouldn't be safe to use them now. I seriously considered starting from scratch and designing a completely new go-kart/buggy with full suspension, forward and reverse gears, a differential and anything else I could think to add. I realised, though, that if I was starting from scratch, I wouldn't use a motorbike engine. I would start with the engine from a quad bike, which would already have reverse built in. However, because of nostalgia, I didn't want to use a different engine and I didn't want to lose all traces of the old go-kart. I decided to build something similar to the old go-kart, using the RG125 Gamma engine, but making some improvements to the old design.
The first step was to get the engine running again. After 13 years of storage outdoors, I decided that it wouldn't be a good idea to try starting the engine. I decided that it would be better to strip down the engine, inspect it and rebuild it. That way, I'd have a good engine to build my go-kart around. I took a sudden whim one day, grabbed my toolbox and angle-grinder and removed the engine from the old frame:

I built a little frame out of wood to hold the engine while I was stripping it. Here it is on the bench before I started working on it:

Due to my lack of funds when I was working on the go-kart originally, I had to do a few bodges on the engine, such as the boot lace in the photo below, holding on the magneto cover.

When I started removing the covers and stripping the engine, a lot of the bolts were obviously corroded in place. The bolts are steel and the engine casings are aluminium so there was galvanic corrosion, as well as simple rust. I sprayed GT7 penetrating oil on everything before I started and gave it a few minutes to penetrate (I find GT7 excellent for releasing corroded fasteners). I was lucky enough to be able to remove a good few of the bolts with a JIS (not Phillips) screwdriver. Any that were too corroded to remove with the screwdriver were placed where I could remove them with a vice-grips.

Magneto Cover Removed

The nuts holding on the cylinder head came off quite easily but when I tried to remove the flange for the coolant hose, one of the bolts snapped.

The cylinder head was stuck to the top of the cylinder so I gently tapped the tip of a thin chisel into the gasket all around until it started to separate and then carefully pried it off.

I was easily able to remove five of the six nuts holding the cylinder to the crankcase but the position of one made it impossible to get a socket on it. I tried various spanners but the nut was quite soft and rounded when I put any serious force on the spanners. I tried a few different methods to remove it but in the end I decided to drill a hole in the side of the nut, then drill with bigger and bigger bits until that side of the nut was nearly drilled away. A sharp tap with a punch on the corner of the nut split the nut open, then I was able to remove it by hand.

Cylinder Removed

Next, I removed the exhaust valve solenoid, then pulled the exhaust valve out of the cylinder:

I removed the piston and small-end bearing:

The next part I wanted to remove was the magneto rotor. I removed the bolt securing it and thought the rotor would pull off easily enough. I couldn't budge it. I gave it a few sharp cracks of a hammer to try to shock it off, but it wouldn't move. Suzuki sell two special tools for removing the rotor but they cost €226 and €44 respectively and are just a slide-hammer and adaptor. I borrowed a slide-hammer with forks that fit into the slots on the rotor. I cable-tied the two forks together to prevent them from slipping:

I tried as hard as I could, even flinging myself backwards with the slide. I nearly pulled the enging off the bench but the rotor never budged. After removing the slide-hammer I noticed that the crankshaft was a little rough turning over by hand and suspected that I had actually shifted the whole crankshaft slightly in my efforts to remove the rotor. Even if I had the special tools from Suzuki, they wouldn't have helped. I realised that I needed some method that would stop the shaft from moving while I pulled the rotor. I decided to make an adapter that would allow me to fit a large bearing puller to the rotor.

When I tightened the bearing puller, the mild steel I had used to make the adapter just bent:

I welded on extra bits of angle iron, but the metal just wasn't strong enough:

I started looking for a bearing puller that would fit into the two slots on the rotor. I visited a few different bearing shops around the country. Any puller I looked at was either too big, and wouldn't fit, or too small and would probably break under the pressure. I was working in Clonmel one day and found a cheap bearing puller (about €20) that looked just about perfect. The ends of the forks were almost the perfect shape and size to fit into the slots on the rotor and the puller was big enough to withstand the force I'd be applying. When I got home, I had to grind about a millimeter off the corners of the ends of the forks to get them into the slots but it wasn't enough to weaken the puller in any way.

I fitted the bearing puller to the rotor and started tightening it. I could feel the tension building in the puller as I tightened but the rotor wasn't moving. I started getting nervous that something would break. I was slowly applying more pressure when there was a sudden loud crack and I felt the puller come loose and fall on the bench. I thought the puller had broken but after blinking a few times I saw that the rotor was still attached to the puller and had come free from the shaft.

Magneto Rotor Removed

After that, the engine came apart easily enough:

Oil Pump

Stator and Oil Pump Removed

Inside Neutral Position Switch

Neutral Position Switch dismantled and Removed

Water Pump Casing Off

Clutch Cover Removed

Suzuki say you need a special tool to remove the clutch springs but I was able to remove them with a normal spring puller and a pliers. I think refitting them is going to be a lot trickier, however.

Clutch Pressure Plate, Thrust Bearing, Drive Plates, Driven Plates and Push Rod Removed

There's a special tool to hold the clutch sleeve hub while loosening the hub nut but I just bolted the chain sprocket to a piece of angle iron, fitted it to the engine and put the engine in gear to stop the engine from turning over while I loosened the hub nut:

Clutch Sleeve Hub Removed

Clutch Basket Removed

Kick Starter Gear, Oil Pump Shaft, and Gearshift Mechanism Removed

Water Pump Drive Gear and Primary Drive Gear Removed

Storing Crank Case Bolts and their Positions

To split the crank case, I had to carefully pry the two halves apart. I started by running a Stanley knife along the split to cut into the gasket/sealer. I then worked around the crankcase with a wide, sharp chisel, using it to wedge the split open more and more as I worked around. The crankcase is aluminium, so I had to work very carefully to make sure I didn't damage the edges. Once the case was separated all the way around, it was simple enough to ease the two halves apart.

Crankcase Open

Inside the crankcase was in fairly good condition but I was glad I opened it because there was a lot of gunge inside from the old oil.

Countershaft and Drive Shaft Out

Nearside Half of Crankcase Empty

Offside Half of Crankcase Empty

Engine Dismantled

25 August 2019
After months of doing nothing with it, I've finally started rebuilding the engine. The perfectionist in me wanted to replace all the bearings in the engine as a matter of course. The economist in me, however, looked up the prices of all the bearings and realised that it would cost approximately €250 just to buy the bearings and oil seals. If I was rebuilding the engine to put it into a motorbike, I wouldn't hesitate to replace all the bearings but this is for a go-kart and the project would start to get expensive very quickly if I allowed it to.
A lot of the bearings and oil seals are standard sizes and can be found cheaper than from Suzuki. A few of them, however, are unusual sizes which are only made by Suzuki. The big-end bearing, for example, is €52.50. There's also a small roller bearing in the transmission that costs €31. I went to my local bearing specialists and bought good quality (FAG) bearings to replace the standard sizes in the engine. They cost me just under €50. I also got the standard-sized oil seals for a few euro. I inspected the non-standard bearings and found that all of them were perfect and didn't need to be replaced. I bought the non-standard oil seals and an exhaust seal for €34 so all-in, the parts for the engine rebuild cost about €90 (so far!).
I tapped the old bearings out of the crankcase, using a suitably sized socket as a punch. The crankcase had a lot of gunk and crap inside it, so I cleaned it out using a combination of carburettor cleaner, brake cleaner, cloths and compressed air. I also cleaned the fitting surfaces of the crankcase with 000 grade steel wool to remove any traces of old gasket sealant.
I applied blue thread locking compound to the oil seals and pushed them into place using a socket and extension bar. Then I gently tapped the new bearings into the crankcase, in each case using the old bearing as a punch so that I could be sure that the new bearings were seated properly but without the risk of damaging them. I also cleaned and fitted the kickstarter shaft.

There was some light corrosion in a few places on the surface of the crankshaft, so I removed that with steel wool. I cleaned off the gunk with carburettor cleaner, then installed the crankshaft in the crankcase.

There was a lot of gunk on the transmission parts, as shown in the photo below, so I cleaned them with carb cleaner and brake cleaner. I found what looked like chewed up grass cuttings between the teeth of the gear cogs. I don't know if that got into the engine somehow while it was still in use, or if it was some kind of algae that grew in there when it was idle.

After cleaning the gear-shifting cam, I noticed that a dowel pin had fallen out of it. It had been there when I started cleaning the cam, so it must be somewhere nearby. After an hour of searching I decided to stop for the evening. This morning, I started to search for it with new impetus. I was determined to find it. I searched all over the floor again, then pulled everything out from under the bench and made sure that it wasn't anywhere there. I emptied my toolbox to make sure that it hadn't fallen inside. I even hoovered everywhere and then passed a magnet through everything that the hoover had picked up. After two hours, I was 100% sure that it wasn't in the garage. I had taken the cam to the door to blow it clean with the compressor. If the pin had been blown out onto the gravel, it would be nearly impossible to find. I have a spare gearbox, so I decided to take the dowel pin out of that. I started opening the spare gearbox but it's quite rusty, so I soon realised that opening it would be another project in itself. I decided to make one last desperate search in the gravel outside the door. I grabbed a large welding magnet and started scrubbing it back and forth across the gravel. After a few minutes, I couldn't believe my luck when I saw the dowel pin skittering across the gravel. It only took a few more seconds to follow it and find it.

With the dowel pin back in place on the gear-shifting cam, I installed the transmission shafts and gears, the shifting cam and the gearshift forks.

I bought a full set of gaskets and o-rings for the engine but when I opened it, I was surprised to find that this didn't include a gasket for the crankcase. I cleaned the fitting surfaces with alcohol, applied gasket compound and closed the crankcase. I don't like bolts with Philips, Pozi or JIS heads as they are very difficult to open when tight/corroded, so I bought bolts with socket heads to replace the JIS bolts on the engine.

Crankcase Closed

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