RE: Engine piston wont cycle
ST like to make their engines with the piston coming within around .010" from the top of the liner and the head sitting flat on the liner. Put a straight edge on top of the liner and turn the piston to TDC and see if it lifts the straight edge. There should of course be a very small gap between the piston and straight edge. If the piston lifts it off the liner then GaryHarris nailed it with the wrong rod. There's no way a glow plug can extend far enough to foul the piston in an engine of that size. If the rod is the wrong length then the top of the piston will also sit slightly higher than the bottom of the exhaust port with the piston at BDC.