Prepare for the FAA Powerplant Written Test. Study with flashcards and multiple choice questions, each featuring hints and explanations. Ace your exam with confidence!

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During a 4-stroke cycle, which event occurs at about 60 degrees after BTC?

  1. The exhaust valve opens

  2. The intake valve closes

  3. The intake valve opens

  4. The spark plug ignites

The correct answer is: The intake valve closes

In a typical 4-stroke cycle, the timing of various events is crucial for the engine's efficient operation. At approximately 60 degrees after Bottom Dead Center (BDC) during the power stroke, the piston is moving back up in the cylinder after having just performed its work by pushing the exhaust gases out during the previous stroke. Around this point in the cycle, the intake valve closes after the intake stroke, ensuring that the freshly drawn air-fuel mixture is sealed into the combustion chamber for ignition. Closing the intake valve at this stage is essential as it prevents the mixture from escaping and prepares the chamber for the ignition process that will follow shortly. Understanding the timing of the valve operations is critical for performance and efficiency in an engine. By correctly identifying the closing of the intake valve at about 60 degrees after BDC, one recognizes how the different strokes of the engine are carefully sequenced to maintain optimal combustion and power production.