I'm pretty sure this is the sequence of events that happened to my '87 300E. the other day when I started her up immediately ran violently rough heard some metal contact and shut car down. pulled the valve cover and all valves looked fine; yanked the spark plugs and all but #6 was fine -- it had scrapes and scratches on it, and was bent a bit but strangely enough, the gap had not changed. check tail pipe and water was inside. pulled the fan clutch and turned crankshaft manually and motor seemed to turn just fine. next day I replaced #6 plug and car started up a bit easier this time but still ran rough with a light tapping sound heard. again, #6 plug was scratched and scraped, but gap was unchanged.

Does this sound like a bent piston rod? If piston is hitting plug, why is the gap the same? Could timing have been thrown off somehow?

Last couple of questions.... if it does turn out to be a bent rod, and I do the head r&r, how much is involved after pulling head and replacing the bent rod? What type of bill would I be expecting to pay?

thanks all, I really love this site

joe