Greek sellers – maybe it gets lost in translation, but in my experience “good condition” often has a different meaning in Greece, so usually I had to buy twice. Sorry, no source for used AX1 parts that I could recommend.
Ok, mass out’s tensioner fix viewtopic.php?t=2534
I'm really bad at video acoustic diagnosis , but this does not sound like a faulty tensioner or a worn out cam chain to me. In your case the chain produces a bit of rattling, but nothing to worry about. The hard, clacking sound points to something more sinister, I’m afraid. But as said, I’m not any good on that and sometimes the sound on that videos is misleading. On my videos my NX sounds really strange, but that’s due to the video editing.
What you can do: check the oil filter for any kind of flitters. If they are non-magnetic, it’s aluminium when a loose cam chain is chewing at the cylinder. Magnetic flakes may come from the lower conrod bearing, that’s very rare but it produces a hard clacking sound like this.
After that take a close look at the cam chain & tensioner, check the timing, valve play etc. viewtopic.php?t=2529 With the head cover off and a torch try to take a look at the cam chain sprocket a the crankshaft
If everything is ok with the valve train and the clacking persists you could pull the head and cylinder to check the conrod bearings.