4.3 Two-stroke petrol engine

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

“What are the operating principles of two-stroke petrol engines?”

The titles are open to everyone. Reading a lesson needs an account — sign in or create one.

1. A push every turn
   40 min · 1 practice tasks · quiz
   Say where two-stroke engines are used and why one turn of the crank gives one push.
2. No valves, only ports
   40 min · 1 practice tasks · quiz
   Name the parts of a two-stroke and the three ports in the cylinder wall.
3. The three ports and the piston valve
   40 min · 1 practice tasks · quiz
   Say what each port does and how the piston sets the timing.
4. Up: squeeze above, draw below
   40 min · 1 practice tasks · quiz
   Describe the up-stroke: the cylinder is squeezed while the crankcase draws fresh mixture.
5. Down: fire, then scavenge
   40 min · 1 practice tasks · quiz
   Describe the down-stroke: the plug fires, then the crown uncovers the exhaust and transfer ports.
6. 360 degrees, one push
   40 min · 1 practice tasks · quiz
   Join the two strokes into one cycle of 360 crank degrees and count the pushes.
7. Oil in the petrol
   40 min · 1 practice tasks · quiz
   Explain total-loss lubrication and mix two-stroke oil to the card of 50 to 1.
8. How the mixture gets in
   40 min · 1 practice tasks · quiz
   Compare piston-ported, reed-valve and disc-valve inlets, and name the magneto.
9. Tools and the strip order
   40 min · 1 practice tasks · quiz
   Name the overhaul tools and the safe order for stripping this two-stroke.
10. Read it before you measure
    40 min · 1 practice tasks · quiz
    Read a seal leak, scouring, carbon, corrosion, cracks and bends on a two-stroke.
11. Bore, ovality and piston clearance
    40 min · 1 practice tasks · quiz
    Measure this cylinder against a 40.05 mm bore card and check the piston clearance.
12. Ring gaps and the locating peg
    40 min · 1 practice tasks · quiz
    Check the free gap, side clearance and working gap, and fit the ring over its peg.
13. Big-end, side play and the crank seals
    40 min · 1 practice tasks · quiz
    Check the big-end and side play and explain why a crank seal leak is serious.
14. Seal it, gap it, torque it
    40 min · 1 practice tasks · quiz
    Assemble the two-stroke with new seals, rings set on the peg, and the card torques.
15. Smoke, shake, knock and no start
    40 min · 1 practice tasks · quiz
    Read the common running faults of a two-stroke and know when to stop.