Hi, I have a couple of older bikes (an RD250 and RD400) that both consistently have small amounts of metal in the oil. There are no large chunks or flakes, it's more like a fine metallic dust. If you pour the oil, it appears reasonably clear and you can't see the metal.
Both bikes have magnetic drain plugs, and usually there is just black sludge on the magnet, which leads me to think maybe the metallic stuff is aluminium.
The 250 has covered 40,000km since its last full rebuild (yikes), so I've always assumed the metal is just a result of general wear and tear through the gearbox. The 400 has just had a rebuild, but I didn't replace any gearbox components as they seemed OK upon inspection. But I wasn't really expecting any metal to be present in the oil after 3-400km of riding.
This leads me to the question of: how much (if any) metal is considered "normal" to see when draining motorcycle gearbox oil?
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