Here's a tip that came in the instruction leaflet for my new Enya 61 ringed engine. First insert the piston into the bottom of the liner so the ring has just barely been compressed. This allows for a lot of sideways movement (wobble) of the piston and rod. Then fit the liner down into the crankcase until the rod can slip onto the crankpin then slide the liner the rest of the way down over the piston. Enya obviously understand that guys will always strip an engine and they even give instructions on a tightening sequence for the head.