In my 86 300E I always run 91 octane ( the highest generally available here in So. Calif.) but I still hear pinging. I've tried all the different brands of gas and none of them seems to make any difference. I've also tried using Techron several times over as many months with no results. It's usually not that audible, but If I'm accelerating near a wall or parked cars the noise is reflected back at me and I can hear it quite clearly. It's also noticeable while accelerating up long freeway grades. It seems to occur even under normal acceleration and I worry about the long-term effects, especially after reading about the "190E Disaster"

http://www.peachparts.com/shopforum/showthread.php?threadid=83621

Is there a way to retard the timing slightly, or to remove carbon buildup on the pistons and combustion chambers without pulling the head? (not sure that I have an excessive amount, but it couldn't hurt to remove any that's there)

For that matter, does anyone know a source for a reasonably priced fiber optic device that could be used to inspect the inside of the combustion chamber through the spark plug hole?

Gary