MOPED ARMY

Just to clarify : the rod should be able to slide side to side a bit , with little if any addition play at the small end .

Side to side is fine. In and out is bad news.

There’s a lot of space in the crank case itself for piston chunks to sit in and not do too much damage. If piston got stuck in your crank shaft itself I would imagine you would see much more damage than what you’re describing.

A piston & cyl run on a d crank?

Measure the stroke.

it's kinda hard to measure the stroke because the plug hole isn't straight on and you can't remove the head with 1 piece jug. The engine tage even if it doesnt say ABC orD will say 47 or 49cc - 49 is the 44mm stroke D crank. The quickest check if you suspect it's been maybe swapped, if it's a square C/D cylinder, look up into the exhaust port at BDC and if the piston hangs over the bottom by ~1mm it's probably the shorter crank.

It's awkward trying to measure stroke outside the bike with the jug off. The other telltale if you have the crank outta the cases is the location of the bigend bearing - on the D the bigend rod lines up right next to the taper on the cheeks, the ABC 42mm crank the bigend is close to the center of the cheeks with some space before they taper off. Search for crank diffs or look in the wiki on sachs motor differences for photos