Internal combustion and mobility

Compression is everything, and compression means piston, rings and bore held to tolerances a tier tighter than a steam engine. The clearance between piston and bore is measured in hundredths of a millimetre, and the bore must be round and parallel to match.

Do not start until the machine tools can bore a cylinder round and parallel to a few hundredths of a millimetre, grind rings, and until gauges exist to check both. Measure a test bore before designing the engine around it.

Low speed forgives poor balance and poor materials. A stationary gas or oil engine running at a few hundred revolutions a minute, driving a mill, pump or generator, is a far easier first target than a vehicle.

Use a low compression ratio — roughly 4–5:1 for early spark-ignition engines on poor fuel — so the fuel does not knock. Heavy flywheels smooth the power strokes. A thousand hours of reliable stationary running is the proof before any vehicle work begins.

• Hot tube — a closed tube heated red by an external flame, igniting the charge when compressed into it. Simple and self-contained, and an open flame beside the fuel.
• Magneto — a magnet and coil turned by the engine, generating its own spark. Needs no battery, and is the robust choice for field machinery.
• Coil and battery — easier timing control, but dependent on the battery.

Set ignition timing by test: advance until power stops rising or knocking begins, then back off.

Cooling and lubrication kill more engines than combustion problems.

• Lubrication: a pump or splash system that reaches every bearing, piston and cam, an oil pressure or flow indicator the operator can see, and oil changes on a logged schedule.
• Cooling: water jackets with a radiator or tank, holding coolant roughly 70–90 °C — too cold wastes fuel and sludges the oil, too hot scores the piston.
• Bearings: plain bearings need a good bearing alloy and clean oil; rolling bearings need hardened, precisely ground balls or rollers. Bearings, not cylinders, usually limit engine life.

Exhaust contains carbon monoxide, colourless and odourless, and it kills in an enclosed space within minutes, often while people sleep.

Duct the exhaust outdoors through gas-tight pipe, ventilate the engine room, and never run an engine in a closed building, shelter or tent. A petrol engine's exhaust is particularly rich in carbon monoxide.

The diesel cycle compresses air alone until it is hot enough — at compression ratios around 14–22:1 — that injected fuel ignites without a spark. It runs on heavier, safer fuel at better efficiency, and suits tractors, boats and generators.

It demands still higher precision, above all in the injection pump and nozzles, which meter tiny quantities at very high pressure. Filter the fuel finely — dirt destroys injectors. Keep hands away from injector spray: it penetrates skin and causes serious injury.

A tractor releases farm labour to everything else — the largest structural change available at this tier. Put the first engines on ploughing, threshing, pumping and haulage.

Then think hard about layout. Cheap personal mobility historically reshaped settlements around the car and produced sprawl, dependence and a large ongoing energy demand. That was a set of choices, not a technical necessity. Decide, in published rule, whether the settlement is planned around walking, rail and freight, or around private vehicles — see Patterns.