engine knocking

Before you tare it down look for lose parts on the quad that are ratling. My kick starter was doing that and i almost took the engine out for no reason. Check your pipe, kick starter, engine mounts, footpegs, anything like that.
 
Broken rings will only cause loss of compression and possible lots of blow-bys, thus causing the burning of oil and gas in the oil (as there is not a PCV in quads).

Most likely you ran it low on oil, and thus the rod bent...