If timing is off, what is the tendency of engine knocking?

• A. Timing off reduces knocking
• B. Timing off can cause knocking due to abnormal combustion
• C. Timing off only affects idle
• D. Timing off improves fuel economy

Answer: (B)

Timing plays a big role in when the air‑fuel mix burns inside the cylinder. If the spark fires too early, the mixture starts to burn before the piston reaches the optimal point. That causes a rapid, uncontrolled rise in pressure while the piston is still moving upward, sending pressure waves through the cylinder that collide with the piston and create the sharp, knocking sound. This is abnormal combustion—the energy release isn’t synced with the piston’s motion. Retarding the timing can reduce knocking but at the cost of power and efficiency. So, when timing is off, knocking tends to occur due to abnormal combustion.