Yamaha F100B F100C Outboards Factory Service Manual, Page 99Get this manual
Power unit Checking the valve clearance
1Remove the flywheel magnet cover 1, cover 2, disconnect the high-tension cords and fuel hoses 4, and then remove the spark plugs3Loosen the tensioner bolt 5, and then remove the timing belt 6, driven sprockets 7, and cylinder head cover 8
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2Turn the flywheel magnet clockwise and align the TDC mark on the flywheel magnet with the pointer b, and check that" marks and on the driven sprockets are aligned