Automotive Service Excellence (ASE) A8 Engine PerformanceGeneral Engine DiagnosisMedium
A client complains of a loud, rhythmic 'tapping' or 'ticking' noise coming from the top of the engine, which increases in frequency with engine RPM. The noise is more pronounced when the engine is cold and tends to quiet down slightly as it warms up. What is the most probable cause?
- AExcessive valve lifter clearance.
- BA worn main bearing.
- CA cracked flex plate.
- DA loose connecting rod bearing.
Show answer & explanationAnswer & explanation
Correct answer: A. Excessive valve lifter clearance.
A rhythmic tapping/ticking noise from the top of the engine, increasing with RPM and more pronounced when cold, is characteristic of excessive valve lifter clearance or worn hydraulic lifters that are slow to pump up with oil. As oil warms and thins, they might quiet slightly.
Why the other options are wrong
- B. Worn main bearings typically produce a deep 'thump' or 'knock' from the bottom of the engine.
- C. A cracked flex plate usually causes a 'clattering' or 'rattling' noise at idle, often mistaken for an engine knock, but typically not from the top of the engine.
- D. A loose connecting rod bearing causes a sharper, metallic 'knock' or 'rap,' often more pronounced under load.
Engine Tapping/Ticking Noise Diagnosis
Identifying the source of rhythmic tapping or ticking sounds in an engine, often indicative of valvetrain issues.
- Top-end noise suggests valvetrain (lifters, rockers).
- Frequency increases with RPM.
- Often more noticeable when cold due to oil viscosity.
Memory trick: Listen to the engine's song, it tells where things went wrong.