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What are the possible causes of a severe engine knock around 2-3k rpm? The bike sounds fine at idle. I ran the bike low on oil and it's got a knock/clunk/rattle now or the bike started knocking, ran low on oil and got worse. I am wondering where to start troubleshooting. :wallbash: I don't think the engine was leaking when the knock started but it leaks now, possibly a cracked case? The engine has 17,000 miles on it now. Unless it's somehow a cheap fix; it looks like getting an engine off ebay or possibly from craigslist has a good possibility of being cheaper. I am mostly looking for suggestions of where to begin or if I should just start tearing down the engine. I was suggested taking the sump cover off and checking that out.

I changed the oil and used a Yamaha oil filter rode for 2,500 miles with no problems. Right before a road trip I changed the oil and I used a oil filter from Napa, 500 miles into the trip and this all happened, can I blame the Napa filter? (sarcasm)

Feel free to throw any theories and suggestions out there.