2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 128Get this manual
Cylinder head NOTE: Be sure to keep the valves, springs, and other parts in the order as they were removedValve spring compressor 9: YM-04019 Valve attachment 0: YB-06320 S68V5775
Checking the cylinder head
1Eliminate carbon deposits from the combustion chambers and check for deterioration2Check the cylinder head warpage using straightedge and thickness gauge in the directions shownReplace the cylinder head assembly if above specification