Cnuteneering[ ca-noot-en-neer-ing ]
The art or science of making practical application of the lack of knowledge of pure sciences, such as physics or chemistry, as in the construction of engines or cars without suffering any life-changing injuries.

As an enthusiast of models (not the Ratajkowski kind, you pervs) I have a reasonable garage / hangar of 1/10, 1/8 brushless electric motored cars, helicopters and a plane (which I still cannot fly).
Tired of waiting for parts to become available as HPI are currently in bankruptcy proceedings, and wanting to learn more about two stroke engines in general I looked at getting a proper petrol RC car. I have had nitro engines before but I absolutely hate the smell of burnt nitro fuel.

Plus, learning about how to build and maintain a 2 stroke engine is potentially going to be a useful skill in the coming Great Reset, as well as metalworking. I am reasonably good at woodworking and love the smell and feel of working on real, natural wood. Metal has always felt cold and unforgiving, plus a wood splinter will gradually be absorbed into your flesh but metal shards seem to stay forever until they expelled. As such, I have not mucked about with metalwork so much.

For petrol engines, cars are usually 1/5 scale size; why this is, I do not know. I could not find a 1/8 scale petrol model for love nor money. Power curves or something with smaller engines, maybe electric models ate their lunch in the 1/8 and 1/10 scale range.

Looking at 1/5 scale models in the petrol range they are about a grand. No way I can justify that to the Accounts Committee, so home build it is.

This will be a series documenting my progress, (or lack of it) for your delectation and entertainment.

I expect to be counting my fingers at the end of each engineering cycle.

It looks like I have no choice but to build a 1/5th scale car which is going to be interesting as everything is bigger, heavier and usually more expensive. To keep costs down, I will try to make as much of it as I can.
Right now, I have a vague plan, a shed full of tools and a heart full of willing. As the project goes on, I may need to revisit this statement.

Tools I have:
Angle grinder
Grinding wheel

Tools I do not have but covet:
Tap and die set
Piston stopper
Big shed to work in
Metal lathe

Tools I covet, will probably need and have no idea of how to use:
MIG welding kit.

I am thinking that I cannot design anything until I have an idea of how the engine fits together and will fit to the car. It is pointless trying to design something only to find that the exhaust is in the way of a major structural component, so I need to get an engine first.

Looking on Ebay for a cheap second hand 2 stroke engine is like looking for hen’s teeth. Every half decent engine seems to go for 200 quid or more; there are some lovely bits of engineering out there if you have 500 quid kicking about. I did however, find which seems to be a funnel for cheap Chinese tat into Western nations, with a variety of outcomes. Their pricing seems a bit jiggly so have a look at what you want, then clear cookies before you buy and the price will drop to a more attractive level.

I bought a 2nd hand Zenoah Komatsu G2D engine for 62 quid, plus a tenner postage. Then another 20 on import duty (which was only mentioned by UPS, my goods were held hostage until I coughed up). Then again, a tenner for shipping 2.5Kg from Malaysia to my door is pretty amazing price wise.

After a short wait, the engine turns up. In a box held together with packing tape, no instructions or manual or anything:

Komatsu Zenoah Engine and muffler

We have carburettor, air intake filter, main combustion chamber and exhaust… And nothing else. Reading online, these engines need a centrifugal clutch so as to allow the engine to idle when not being driven forward. Hmm.
I cannot find any details on what clutch will fit, so that is Action Point 1 – find a clutch that fits.

Turns out that the clutch has a shoe holder, that bolts on to the drive shaft from the engine. It is basically a disc (or bar) with 3 holes in – one in the middle to bolt on to the driveshaft and then one each side of the centre hole down the line of symmetry. The clutch shoes bolt on to the outer holes, but only one end of the shoes is held still. As the shoes rotate, they push outwards into a clutch bell, which looks a bit like a sink plunger. The clutch shoes brush up on the inside of the plunger, causing the shaft to turn. The shaft then has a pinion (little) gear attached. A complete set is probably going to set me back 40-50 notes, but at least I will get the all important pinion gear turning, which I can then use to feed into my drive train.

This motor is apparently from a strimmer, but has been used in Go-Ped scooters. A maximum RPM it seems of 12,000 which is probably going to be too slow to move the car at the speed I crave. If I can get it to 50MPH I will be overjoyed. This probably means I will have to put some sort of gearbox mechanism in there as it is going to be a heavy beast no matter what I do with it, and decent torque is going to be a must at low speed just to overcome the inertia of it.

I now have the engine, I just need to think how big a frame it will need to carry it. Transmission and steering I will leave for later to worry about. One thing however – a petrol engine turns in one direction only. On electric motors, the speed controller turns the signal to reverse into a series of reversed polarity pulses to the motor, which brings the car to a halt. When stopped it applies gentle reverse current so the car will reverse. Can’t do that on petrol. /rubs chin. Probably going to have to design some brakes as well, then.

As fortune would have it, the petrol tank arrived just as I was writing this. It has two tubes, which is… interesting.

260cc petrol tank

Design goals:
Fast as possible on offroad; too big to have on roads
4 WD
Must be able to reverse, and brake
Unbreakable, or as close to
Must be able to mount GoPro or similar camera on it
Cheap as possible

The initial design layout for the car has one or two minor problems but I think I can work with it:

First layout of the Cnutmobile.

Next up (when I get time to do it) – does this engine even work, and can I get it started?

© El Cnutador 2020

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