4.2 Four-stroke petrol engine

• illustrate the constructional features of a four-stroke petrol engine
• describe the operating principles of a four-stroke petrol engine
• overhaul a four-stroke petrol engine following the correct procedure
• perform fault diagnosis on four-stroke petrol engines
• value the need for four-stroke petrol engines

“How does a four-stroke petrol engine operate?”

“What are some of the faults associated with four-stroke petrol engine?”

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1. What the four-stroke is made of
   40 min · 1 practice tasks · quiz
   Name the main parts of a four-stroke petrol engine and the job of each.
2. Four strokes, two turns
   40 min · 1 practice tasks · quiz
   Place induction, compression, power and exhaust on two turns of the crankshaft.
3. Draw in, then squeeze
   40 min · 1 practice tasks · quiz
   Describe the valve positions on the induction stroke and the compression stroke.
4. The push, then the burned gas
   40 min · 1 practice tasks · quiz
   Describe the power stroke and the exhaust stroke, and count one push in 720 degrees.
5. How hard the mixture is squeezed
   40 min · 1 practice tasks · quiz
   Calculate this cylinder compression ratio from swept volume and clearance volume.
6. Tools for measuring and fitting
   40 min · 1 practice tasks · quiz
   Match each overhaul tool in the design to the job it actually does.
7. Look before you measure
   40 min · 1 practice tasks · quiz
   Read leaks, scoring, soot, corrosion, cracks and bends, and send damaged parts out of service.
8. Bore, stroke and ovality
   40 min · 1 practice tasks · quiz
   Measure this cylinder against a 60.05 mm bore card and a 0.03 mm ovality card.
9. Journal and bearing clearance
   40 min · 1 practice tasks · quiz
   Check a journal and a plastic-gauge clearance against this bearing card.
10. Three gaps, three jobs
    40 min · 1 practice tasks · quiz
    Keep the free gap, the side clearance and the working gap as three different measures.
11. How far the cam lifts
    40 min · 1 practice tasks · quiz
    Find cam rise from a dial gauge and compare it with a 5.5 mm minimum.
12. Strip in order, then price the parts
    40 min · 1 practice tasks · quiz
    Follow one overhaul order and add a parts estimate of 6600 shillings.
13. Put it back to the card
    40 min · 1 practice tasks · quiz
    Assemble the measured engine with paired shells, a ring compressor and the torque card.
14. Why it will not start
    40 min · 1 practice tasks · quiz
    Sort a hard start into spark, fuel and compression without holding a plug lead.
15. Smoke, shake and knock
    40 min · 1 practice tasks · quiz
    Read black, blue and white smoke, and stop the engine on a heavy knock.