Hi, I am a new member of this forum. I have just purchased a 1987 560SL with 94k well documented miles on it. The timing chain, rail, tensioner, and tensioner rail were replaced at 85k miles, about 2 years ago. I bought the vehicle knowing that it has a mechanical problem. It runs very rough & has a fairly loud tapping sound. The seller chose not to have the vehicle repaired.

I did a compression check and cylinder #4 has a very black, apparently fouled spark plug, and the compression seems low. All other cylinders check out OK & spark plugs look OK.

Any recommendations on how I should proceed ? Could this be a bad rocker, or, perhaps a worn cam lobe ?

thanks in advance for your help/suggestions !

Brian