Just got it yesterday... A lapping tool is a tool that lets you very slovly grind down the piston. I have tested it today and started the engine. I think i need to use in on a few engines before i get a hang of it.

There is a few things to think of when using lapping method also. All materials will expand when you start engine first time. Depending on piston material, sleeve material and so on. I do not think it is easyer to learn lapping than the bench, but i really hated the bench brakein.