Must confess that valves go in a drill, clamped in a vice and I use a screwdriver or similar to shift the carbon. Does'nt scratch the valves as they are pretty hard. Finish off with various grades of wet and dry (usually damp with a bit of oil), remove from the drill and then polish on the mop if necessary. Quick and easy.
Pistons and heads get a good scrape (alloy scraper), then wet and dry (with oil again) and finally a polish. As everyone knows, an old ring is broken and used to clean out the ring grooves thoroughly.
One of those areas where you get back what you put in. Pity nobody sees the shiney bits when you reassemble
