well no mater what dont put it down to milage i also have a 2 liter dohc mine has done 250 k yes thats right alot of miles i dont have any knockin smoke or nothink i have a 3 inch cossy exhaust all the way threw on it as well yet still drives like new when i got it home engine flush new oil and filters and so on made it run like a dream try that mate and see what happens then drive it for a few miles calm let everythink oil back up and see

worth a try