🔍 Key Concepts

• Opposed piston engine timing and how two crankshafts are phased relative to each other • Meaning of crank lead (one crank slightly ahead of the other in degrees of rotation) • How changing the phase relationship between upper and lower cranks affects scavenging, compression, and power balance, but NOT their geared speed

💭 Think About

• Think about what a difference in crank lead actually changes: is it power directly, rotational speed, or the timing of events in the cycle? • In an opposed piston design, what must remain the same between the two crankshafts if they are mechanically geared together? • Which options describe a function of timing and phasing rather than something that would require a different gear ratio or separate drive?

✅ Before You Answer

• Confirm that geared crankshafts must turn at the same RPM in normal operation • Recall that lead/lag is measured in crank angle degrees, affecting when ports open/close, not gear ratios • Eliminate any option that would require a different rotational speed for the two crankshafts under fixed gearing