I have a 05' yfz 450 and it recently blew up and I had to replace the pistion, crank and rod, I used the WR 450 kit. The engine runs fine but the oil does not pump back to the tank. Ive cleared out all the return lines checked the oils screen, check oil pump make sure thats working, replaced the seal at the end of the crank where the cover fits over, and still the oil does not return to the tank. Does anyone have any idea what the problem could be??