Hi Justin,

Did you ever figure out what the problem was with this ? Was it a bent valve ? Also, what did the spark plug look like for that cylinder ? I have a 1987 560SL with a very similar problem. It runs roughly and has a tapping noise.....I haven't yet removed the head but cylinder #4 has a spark plug with lots of black deposits on it...the others look good.

Also, assuming that it was a bent valve, did you determine the cause of this ? My vehicle has only 94k orig. miles, the timing chain, guides, tensioner, etc. were all replaced < 10k miles ago. I am thinking that the engine is still in time, as it does turn over just fine.

Thanks in advance,

Brian