https://youtube.com/shorts/XILTEiLTalE?si=tKdvruz5R4Rtg-e1

 

Sounds like loose sheet metal, i.e, exhaust, but if it is from inside the engine, check cam chain is not loose first. You didn't try to drain the oil via the wrong "plug" under the engine did you? A strip down of the top end will probably show what is causing the rattle, if it isn't a loose cam chain.

 

It's for sure inside the front end somewhere it's made the noise since I bought the engine new and has just got worse recently. I've drained the oil with the correct plug My guess was possibly the crank shaft bearings but it runs and drives perfectly fine

 

As I wrote above, sounds like loose sheet metal. I can't remember just how the cam chain guides run on the "Honda Cub" clones, but I would guess at the chain rattling on a guide. Take a look, getting at the cam sprocket is easy. A loose oil filter cover is another possibility, that is on the centrifugal clutch.