never heard that, i used a razor blade scrapper and a wire wheel then cleaned out the crap around the edges with brake cleaner and compressed air.

thats a na block i picked up, it was ran on 87 fuel its whole life and had a egr. the crud was thick, it had to come off.

this is my chipped piston l67 block with like 240,000 on it, pistons are pretty clean, that na engine only has 110.000 on it.