Rmvbeforeflight is on target, the trans fluid (old school dex 3) is the best cleaner you can use, use a lint free rag and wipe bore until there is no dark looking stuff on rag, then when it is totally clean, use 50 weight racing oil on cyl. bores right before installing pistons in bore. Also use the racing oil on pistons and rings when installing pistons in bore, whatever you do don't dip the piston and rings in oil just rub it around piston and ring and install.