TT, I have noticed that there is a wealth of knowledge in the minds and resources of the tt community. I have been looking, researching and reading the threads here regarding my issue at hand and have had no luck finding definitive information. To explain, i have a 2008 YZ450F that started "knocking" while riding a few weeks ago. I was able to limp the bike back to the truck from my "woods" or wilderness riding without any noticeable damage. I have pulled the head, cylinder, engine, etc from the bike and have seen NO noticeable wear or defect that should cause the level of knocking i was hearing. I have since ordered NEW, OEM, Yamaha crank, (rod assy) main bearings, cylinder, piston, all gaskets/seals for complete engine rebuild. I have a manual and am mechanically inclined. My father is very mechanically inclined and even owns a bike shop...focused on Harley's (keep jokes aside) and am curious if there is any thing that i need to know that may be an unwritten or otherwise experience acquirable only things that i need to know. I have yet to split the cases, but was advised by my local Yamaha shop of which are my friends and co"racers" here in Arkansas that my problem will lie in my lower connecting rod bearing. From the topside, i can feel no noticeable play or wear, but was assured that the knock is coming from my crank. I have not been able to inspect tranny as i have been waitin on my flywheel puller to arrive. Please, I am not a novice and do not desire amatuer level responses like check the oil, etc. THis bike has been maintained meticulously had oil, coolant, etc during and previous to the Knock appearing. I am soliciting direct experience, techs, and engineer level information. I have checked spec on piston, rings, etc. The rings are at the end of spec, but not out of spec, the valves are in spec and i will be adjusting upon rebuild anyway. Please send lower end advice as i will be tearing into tomorrow am to put my $1000 worth of OEM parts in there! Thanks to all who can contribute and i hope this information will aid another down the line.