So, i have a new to me 2005 crf450x. Just changed the oil on it for first time myself, and removed the filter to find its installed backwards. I am FUMING. Whats the damage here? :/ It must have been run a while like this by previous owner as oil looks pretty 'used' is the bypass on the filter in case an idiot like the previous owner does this? The top end looks somewhat 'oily' and seems like thatd be the first to go, but i havent torn into anything as it ran fine. I did think the engine sounded a little 'knocky' but put this down to the fact its a high performance race engine with a very short skirt piston. Considering rebuilding before i have a choice. Also found it had a spark plug from a subaru car engine in it, so mad. Idiot previous owner Both these things i could not have realized or spotted while viewing so i guess im unlucky. Feed me the bad news. . .