Cleaning cylinder heads

[Mohamster]

This may sound like a silly question. how clean do I need to get the mating surfaces of the cylinder heads and the liners? There are some really stubborn deposits (I think carbon) that I'm struggling to budge.

I'm worried about getting too agressive with them for example by using a screwdriver or something in case of scratching.

Any tips on tools, products and.methods?

Thanks!!

[itchyfeet]

I use small pieces of folded wet and dry 600 grit with parrafin and spend time

going to try an old barrel with fine grinding paste but that will only do compression surface not o ring surface

screwdriver is a no