My pistons look like this:
http://picasaweb.google.com/lh/photo/IM … directlink
I’ve heard all sorts of different methods for cleaning them. Each one seems to come with a warning. Some chemical cleaners are ok, unless they’re used on alloys. Wire brush and a drill is effective, but be careful not to scratch the heads. Oven cleaner, carb cleaner, aircraft stripper, etc.
I used the nylon brush on my drill to clean one of the pistons. It seemed to clean up well except for a few spots that the brush couldn’t reach. It did leave the top of the piston looking “brushed”, but very gently. Will that texture cause any issues? I’d imagine it would give more surface area for carbon to collect on. But can’t think of anything else it would do.
I’ve also heard that sanding the sides of the pistons is a good idea. Is there anything to this? What grit, if at all?
There are all sorts of ways to clean the carbon off. Simple carb cleaner, engine cleaner, or brake cleaner will all work reasonably well. As will gasket remover. Just spray some on, let it sit a bit, then scrub with a stiff plastic bristled brush. Most should come right off. You can use a scotchbrite pad for the remaining.
It’s usually best to remove the pistons for cleaning so you don’t get carbon debris and chemicals down into the bottom end.
As for sanding the sides of the pistons? No! I would not recommend this. If you are sticking with your used pistons and bores then don’t touch the sides other than a cleaning. Microscopic groves build in the cylinders, rings, and pistons over time and you will have the best seal if those continue to be aligned. If you are replacing your rings for new then it is a good idea to hone the cylinder, which can be done with very fine sandpaper and plenty of oil, or with a ball hone (or at a shop).