I recently got my 98' YZ400F put together after about a year of working on it. I went out to start it up today and could not kick it over after about the third attempt. Thought maybe it was my decompression cable. Long story short, I tore the whole motor apart again to find that I had slightly bent the two intake valves on the outsides. My question: is there a difference between pistons for a YZ and WR or is there possibly a difference in the OD of the valves themselves? I used a 2000 WR head in place of the 1998 YZ head with a new YZ piston. Did I over look something? I know for a fact that I had the valve clearance set to the manuals specs. The manual doesn't call out any differences in the valve clearance specs for those two different years. Any help would be wonderful. Any suggestions about what to replace would be helpful too. Thanks.