Inline-4 Engine
A controlled-explosion air pump
The inline-four is the most common engine layout on Earth: four cylinders in a row, sharing one crankshaft. Air and fuel burn above each piston, and the pressure of that burn pushes the piston down — thousands of times per minute. Everything else on this screen exists to support, time, feed, or clean up after this event.
What it does
Converts the chemical energy in fuel into rotating mechanical energy at the crankshaft, which ultimately turns the wheels.
Mounted in the front engine bay, between the chassis rails.
How it works
- Intake — the piston moves down while the intake valves open, pulling in a mixture of air and fuel (≈14.7 parts air to 1 part fuel by mass).
- Compression — valves close and the piston rises, squeezing the mixture to roughly a tenth of its volume. Compressing it makes the burn far more energetic.
- Power — the spark plug ignites the mixture near top dead center. Pressure spikes to 50+ bar and shoves the piston down. This is the only stroke that produces power.
- Exhaust — the piston rises again with the exhaust valves open, pushing burnt gases out toward the exhaust system.
- The four pistons are phased so one of them is always on its power stroke, smoothing the output into continuous rotation.
Key numbers
| Typical displacement | 1.4 – 2.5 L |
| Cycle | 4-stroke (Otto) |
| Firing order | 1-3-4-2 |
| Redline | 6,000 – 7,500 rpm |
| Thermal efficiency | ~30–40% (rest becomes heat) |
Warning signs of trouble
- Knocking or ticking that rises with rpm — worn bearings or valvetrain.
- Blue exhaust smoke — oil burning past worn piston rings or valve seals.
- White sweet-smelling smoke — coolant entering cylinders (head gasket).
- Loss of power or rough idle — compression loss, misfire or timing issues.
Maintenance & care
- Change oil and filter on schedule — oil is the engine’s blood.
- Replace the timing belt/chain at the specified interval; failure can destroy the engine.
- Keep the air filter clean so the engine can breathe.
- Let a cold engine warm gently before high rpm.
Frequently asked questions
What does the inline-4 engine do?
Converts the chemical energy in fuel into rotating mechanical energy at the crankshaft, which ultimately turns the wheels.
How does a inline-4 engine work?
The inline-four is the most common engine layout on Earth: four cylinders in a row, sharing one crankshaft. Air and fuel burn above each piston, and the pressure of that burn pushes the piston down — thousands of times per minute. Everything else on this screen exists to support, time, feed, or clean up after this event.
What are the signs of a failing inline-4 engine?
Knocking or ticking that rises with rpm — worn bearings or valvetrain. Blue exhaust smoke — oil burning past worn piston rings or valve seals. White sweet-smelling smoke — coolant entering cylinders (head gasket). Loss of power or rough idle — compression loss, misfire or timing issues.
How do you maintain a inline-4 engine?
Change oil and filter on schedule — oil is the engine’s blood. Replace the timing belt/chain at the specified interval; failure can destroy the engine. Keep the air filter clean so the engine can breathe. Let a cold engine warm gently before high rpm.