sounds like the rod bearing might be bad,a top end rebuild wont cost to much to do,you also need to check your driven gear it runs off the oil pump gear it is behind the wet clutchMy 06 prowler 650 was ran low on oil. It now makes a loise which sounds like piston slap. Any ideas on what it can be. Also is it hard to rebuild these engines and do you need special tools. Advise would be appreciated.