During the 500hr maintenance on our 50 SG units we noted oil in the sparkplug bore on 6 cylinders of the first unit. Our Wartsila tech noted these prechambers were lacking a gap between the upper and lower sections and this could be a root cause. The gap exists to ensure that the sealing faces make good contact, and we’re told our prechambers are part of a small population where the rabbet fit had no gap and thus may not provide full contact at the sealing face.
Our prechambers were disassembled and we machined the raised rabbet fit to provide a 1mm gap as instructed. I can’t seem to attach photos here so contact me directly for more details and photos of the area to be machined.
Summary, inspect your prechambers for this approx. 1mm gap between the upper and lower halves, just below the middle O ring groove.