Hello, on my Fiat with Lampredi engine (Oldtimer engine from 1978) the engine was overhauled last year due to piston eaters and water impact of the engine at the engine builder. New oversized pistons were installed with lower dome 4 mm for less compaction. Reason for piston eater: The previous owner had installed dome piston 8 mm, too high compaction, it came to piston eater and water impact at high speed. After now approx. 2000 km again cylinder head was dismantled by me since a valve When I wanted to mount the cylinder head again yesterday when I turned down the piston in cylinder 4 (thermally the most stressed, then the cylinder with piston eater) I found corresponding shades. There is nothing to feel with the finger/finger nail. Is about at half the height with interruptions around. Otherwise I noticed nothing. One possibility: At that time moisture was in Zyl. in the 4. The engine was at the engine manufacturer for some time. There it started to rust and even after drilling, honing, cross-cut this can still be seen, if not felt. Engine builder told me nothing and I didn’t see it at the time. Just reassemble and go or could it be something else? Before I finally took off the head the engine ran very well. Sprang very well, deliver calmly, CO at 2.5 to 3, have Lambdasonde installed around during operation No white smoke from exhaust, etc. Good power development. What is this? Who knows such a picture in the cylinder? What do the professionals mean among you? Thank you and greetings Jürgen