I'm going to be putting my B20 back together again pretty soon.

The motor before had some detonation -- the crowns are kinda
pitted and some of them look like they melted a little. I'm thinking
of taking the pistons to a machine shop and having them chop a mm or
two off of the crown to get a new surface and also to reduce the
compression ratio a little. Is this a bad idea? The pistons in
question are mahle pistons and the crowns seem extrememly thick,
maybe a bit more than 6mm.

Has anyone used zero gap rings from totalseal? A brief bit of
googling indicates that they might not hold up under detonation kinds
of situations. Does mahle sell just ring sets for their pistons?
Any other opinions on new rings for old volvos?

The pistons in question are .040 over mahle pistons with the larger
oil ring gap and the two upper ring grooves are the same size.

thanks for any input,
chris