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Q&A: Clicking engine unlikely to fail

25.11.11

QUESTION: I have a 2006 Honda Accord four-cylinder with 105,000 miles. It has developed a clicking engine noise on a cold start. After the car has warmed up, the sound goes away. I have seen references to a condition called "piston slap." Is this something that I need to have checked out or to be concerned about?

ANSWER: Is it piston slap, valve train noise or some other problem? Using a mechanic's stethoscope to locate the noise would pinpoint the source. Clicking or a sharp tapping from the valve cover on top of the engine would point to a valve train noise. A dull tapping or slapping sound from the side of the engine block would point more toward piston slap. Piston slap occurs on a cold engine when clearance between the piston's lower skirt and cylinder wall allow the piston to rock slightly on the downward power stroke and slap against the cylinder wall, generating that slightly duller tapping sound.

Another possible cause is called CCDI, or combustion chamber deposit interference. This cold-start noise is caused by a carbon buildup on the crown of the piston and roof of the combustion chamber, causing physical contact and a relatively sharp click at the very top of the piston travel.

Source: The Idaho Statesman