I ran into some issues on my YFZR. The cranks blow on these motors; hence, why there is an updated part number for replacement and the WR cranks are popular for the yfz motors.
Usually the rod and crank have an issue with oil and the rod tends to start shaving the crank. I was at Baldwins and saw this first hand. Sure enough my engine blew and it was the same thing. It looked like you shaved a chunk off the C-rod. Check the water pump inpellar too. My was chewed up pretty bad. Look at the valve springs, crank bearings, shims, cylinder, etc. You never know where the metal may have come from. I just started replacing everything that looked the slightest bit scuffed/fatigued. If you're in there, why not freshen things up.
2009 YFZ450R
Baldwin, DID, DP, Houser, JB, Maxxis, PD, PCV, PEP, LSR, Rath, RPM, Sparks, SSI, SunStar, Works Connection
Special thanks to Baldwin Motorsports, PEP, SSI Decals, & my checkbook!!