while I am doing my head gasket, I decided to clean the piston tops because I couldn't stand looking at them.
#4 cleaned up real easy (rag and brake cleaner). #1 proved to be a pain. I got a chisel type scraper from the parts store that said it was for cleaning carbon and scraped the carbon away very carefully. It's not completely clean but way cleaner than it was. On the other hand it has some scratches that were unavoidable to create, but none that catch my fingernail (so I guess they don't qualify as "gouges").
Few random thoughts before I turn the motor over and get to the other two.
- Is this a good or bad idea in general. The only con I have read involves the rings potentially digging into what they are seated in due to the sideways motion of the piston, then causing oil use and blowby, but I don't know if that is genuine advice or just a scare story. It seemed like a good idea to clean the pistons since a new head is going on it.
- Some have said that it is necessary to leave a 1/4" ring of carbon aronud the outside of the piston. Is there a reason for this, or is it just to keep from nicking the cylinder wall trying to remove every last bit. On the first cylinder I cleaned, the small amount of varnish that was in there came right off (- probably because this was the one the water was leaking into. :D ) so there would have been no outer ring to really save.
- Others have mentioned a ring of carbon around the top of the cylinder needing to be left alone. Is this the same as the normal cylinder wear ridge? If so, why would it hurt to remove it? (I haven't yet, but maybe my gasket scraping at the top of the cylinder might have disturbed it.)
- Will 600 grit clean up the scratches I've made on the piston head, or should I even bother trying to clean them up? What about pock-marks/craters on the piston that had the coolant leak, leave them alone or try to sand them out? I don't know if light scratches can become hot-spots, but I'm pretty sure the pock marks can.
- Should I use any kind of treatment/coating on the piston head once it's clean?
- Anything better than brake cleaner as a carbon solvent? Is it safe to use Berryman B12 in an existing installation for this purpose or is that only for teardowns. Someone suggested ammonia but NOT anything containing lye.
The Isuzu 4cyl block has 200k on it. I suspect some of the above might be lore left over from pre-moly-ring days when it was way harder to get a good ring seal, but I wanted to make sure I'm not doing something incredibly stupid.
Thanks.