Cheap ... is right!I recently finished rebuilding a Yamaha Blaster ATV top end that had one of those cheap Chinese kits installed in it.The Aluminum piston was so soft (probably made from recycled scrap materials ), that it couldn't even support the rings.Take a "close" look at the pictures below . . . The ring ends hammered away at the soft aluminum ring lands, until the grooves were spread far enough apart to allow the rings to rotate past their locating pins, eventually finding & snagging the exhaust port . . . causing catastrophic damage.~ Also note the crack that developed in the wrist pin boss.Likewise, the metal used in the cylinder wall liner is softer then what's in the Yamaha cylinders . . . A bore job will not last near as long as what you can expect out of a Yamaha cylinder.