OK -- that sounds like the cage. It is the usual failure point. The cage holds thge balls within the races at a specific separation from each other. The balls rub against it a bit while the bearings spin & eventually the cage wears through in places -- scattering bits of metal into the interior of the engine. Some of these bits get sucked (pushed) up into the upper cylinder during the induction process.

If you are lucky, they don't get caught by the piston as they pass through one of the transfer ports, or in pass out through the exhaust port. They ding up the piston crown & the underside of the cyl head. The engine will survive that damage.

However, if they get caught by the piston while passing out of a port --- goodbye motor.