I have a question and to say the least I am a little concerned.
I bought a 1999 yz400f about 4 months ago in good condition. It runs great, starts 1st - 2nd kick (COLD) and usually always first when hot. It doesn't make any strange noises or blow any smoke, hauls arse and has a gut load of compression. (Apparently it had a new top end put in about 10 months ago.) Since then from me it has done roughly 3-4 hours and from the previous owner roughly (15 hours).
On with the story. My concern, I drained the oil not long ago to find a metallic sheen in the oil with lots of tiny metal flakes at the bottom. The oil filter also had a fair bit of metal in it too. It is shiny and mostly non-magnetic (aluminium I assume?). Their are some steel fines but only an amount that would appear normal from a periodic oil change. So I cleaned the oil filter replaced the oil filter O-rings and the oil filter cover O-ring.
To be extra cautious I filled the bike with Castrol mineral motorcycle oil and took the bike for a ride for about 10 - 15 mins. I re-drained the oil only to see it was reasonably dirty and had less metal flakes in it than before but still had a fair bit. I replaced the oil filter with a new one and refilled it with fully synthetic 4 stroke motorbike oil. Since then I have run it for about 20 - 30 mins. Still makes no noises or smoke and starts easy.
I really need some advice, I have heard that the clutch can cause this but I am not sure. Any signs that it could be something else or just well overdue for an oil change ?
Please any help or advice is much appreciated. Thanks