[brucepick]

These Civics can also get a hard carbon buildup on the cylinder tops that the valves hit against when they open. It sounds a heck of a lot like "knock" or ping.

My wife and my carpool buddy both insisted my Civic was pinging. I tried retarding the timing to various degrees with no success. At one point I had it retarded so much that it ran poorly and gave a check engine light due to lousy combustion; I promptly set it back to a more normal amount of advance. Still made the noise but ran stronger.

Mine finally had enough valve trouble that it needed a head rebuild, and when my buddy got the head off I found a huge buildup of hardened carbon on all the cylinder tops. Easily a 1/16 inch thick of HARD stuff, which I removed with considerable effort. After the head rebuild the persistent "knock" was gone.