MOTOBECANE Z - MOTOCONFORT U 125cc & 175cc

Bonjour a tous !
I wanted to change the oil of my newly purchased bike and found a lot of metal inside
Took off the bottom plate and the cilinder and head. No damage was found. But i'm curious about the bolt on the picture below .. did this come of somewhere or did it manage to get in the engine by accident ?
I checked every exploded view and repair manual a few times but didn't found anything :/
It's a M4

It's a 125cc eninge from the z'series (1956)



Friendly greetings

Never see square bolt in this motor

hi,

for the square bolt, I do not see where it can come from ???
for the other, is not it an engine foundry waste?

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pour le boulon carré, je ne vois d'ou cela peut venir ???
pour l'autre, n'est ce pas un dechet de fonderie du moteur ??