Engine Fundamentals & Mechanical Systems
Four-stroke cycle, engine components, timing systems, valve train, compression testing, and cylinder head servicing procedures.
- Describe the four strokes of the internal combustion engine cycle
- Explain the function of the timing belt/chain and variable valve timing
- Identify causes of blue smoke, white smoke, and black smoke from exhaust
- Perform and interpret compression tests
- Describe proper cylinder head bolt torque procedures
Leçon 1
The Four-Stroke Cycle & Engine Components
How the Engine Works
The modern gasoline engine operates on a four-stroke cycle - intake, compression, power, and exhaust. Understanding this cycle is fundamental to diagnosing every engine problem you will encounter.
The Spark Plug
The component that creates the spark to ignite the air-fuel mixture is the spark plug. It receives high voltage from the ignition coil and creates an electrical arc across its gap. The typical gap for most spark plugs is 0.028-0.060 inch, per manufacturer specification. Always check the service manual for the exact gap.
Compression Ratio
The typical engine compression ratio for a modern gasoline engine is 10:1 to 13:1. This means the air-fuel mixture is compressed to one-tenth to one-thirteenth of its original volume before ignition. Higher compression ratios generally produce more power and better efficiency, but require higher-octane fuel.
Engine Detonation
Detonation (engine knock) is caused by premature ignition of the fuel mixture before the spark occurs. This abnormal combustion creates destructive pressure waves inside the cylinder. Common causes include low-octane fuel, excessive carbon buildup, lean mixture, or over-advanced timing.
The spark plug ignites the air-fuel mixture. Modern gasoline engines have a compression ratio of 10:1 to 13:1 with typical compression pressure of 125-175 psi. Detonation occurs when fuel ignites prematurely before the spark plug fires.