Subject Car is my 1980 450SL, 201,100 miles. Okay, so my car has new injectors, plugs, wires, cap, rotor, WUR...

STILL, cylinder ONE is missing and the new plug is BLACK (sooty and dry black). It is obviously the missing plug (all others are clean).

Compression on cylinder one is GOOD (144 psi) and in line with all other cylinders (which are mostly between 143 and 145).


So I pulled the valve cover today, and pulled apart the rockers, springs, etc. of cylinder one. I removed, and put on new valve seals, though the old ones seemed okay (isn). There seemed to be very little play in the valves. The intake valve rotated easily, and the Exhaust valve would rotate, but not as easily.

BUT here's what I also found: When compressing the EXHAUST valve spring for cylinder one, it would freely compress a few mm, then it would seem to stick for a mm or two, then compress further freely. As if it had a bump.

I am guessing, but this seems to me to indicate a warped or bent valve stem. Yes?

Could something else cause this? Someone in the shop commented that they thought my plug fouling was due to an exhaust problem with this cylinder. I suppose a bent/sticking exhaust valve could be the culprit?

Car is my 1980 450SL, 201,100 miles. It is running excellent except for the loping/missing idle.

To hear it (youtube):

https://www.youtube.com/watch?v=DMP72a45nP0

Above 2500 RPM, it's smooth as silk. Under 2000 it gets a bit rough. Unfortunately, smog on the dyno ends up being around 1500 (and I am not passing smog).


SO: If you have experience with a warped/bent valve stem, or any other cause that this seems like, PLEASE comment. I really would like to determine what is causing the misfire in this one cylinder affirmatively before I go off merrily ripping the head off...