The piston/cylinder holds the rod in position.
There are slight shoulders on each end of the crank pin location.
As long as the rod is in position over the crank pin, the needles or rollers cannot come out because of the shoulders.
At assembly, the needles or rollers must be stuck onto the crank pin with grease so you can slide the rod over them.
At disassembly, you cannot get the rod completely off the crank unless the crank shaft is completely removed from the flywheel side of the crankcase.
The 35 and 40cc Quadra engines from North American chainsaws of the late 60's through early 80's were made this way. They were used in the more modern looking Lumbards and other chainsaws of the period. These chainsaws had a clamshell engine design but the cases were metal as plastics still were not stable enough.