🔍 Key Concepts

• Indicator diagrams showing cylinder pressure vs. crank angle (solid line = actual, dashed line = desired/normal) • Effect of retarding fuel injection timing on the location of peak pressure relative to TDC (Top Dead Center) • Effect of thicker connecting rod shims on compression ratio and maximum cylinder pressure

💭 Think About

• Compare, in each option, where the solid-line peak pressure occurs relative to the vertical TDC line and the dashed reference curve. In which diagram is combustion starting too early and peaking too high? • Think about how retarding timing will shift the pressure curve: will it move the peak closer to, or farther after, TDC? Which diagram shows the opposite condition that needs to be corrected? • Thicker shims slightly increase clearance volume and lower compression pressure. In which diagram is the maximum pressure clearly above the normal (dashed) curve so that a reduction is desirable?

✅ Before You Answer

• Identify which diagram shows peak pressure occurring too far before TDC compared with the dashed curve – this points to over‑advanced timing. • Identify which diagram shows maximum pressure significantly higher than the dashed reference curve – this suggests compression/firing pressure is excessive and could be reduced with thicker shims. • Confirm that the chosen diagram shows both: early combustion (peak shifted toward the left of TDC) and an overly high peak compared with normal.