Hello folks,

I have a euro W126 280S with an engine rebuilt 80 000km ago. This is a fact.

My compression test show 11.3 bars +/- 0.2 bars for 5 cylinders and ONE cylinder (number 3) at 8 bars . Add oil, it gets up to 9.5.

My first reaction was : broken ring . But then I thought: why did this happen ? It seems unlikely tp me.
The plug tends to oil foul in that cylinder but not really oil soaked, just dark - humid

The coolant looks ok if a bit smelly. Could this be a head gasket without a leak into the coolant ? The idle is rough but the engine turns over quite smoothly at some speeds.

Could a valve be cracked ? I had to install thinner pressure pieces to get the valve gear to be in spec. Maybe a valve was damages...

Any tips/ diagnostic approaches appreciated before I decide to pull the head.

Cheers

Denis
Lion sur Mer
France