2009 Yamaha F40 Outboard Service Manual, Page 217Get this manual
Power unit
Valve spring tilt b: 1.7 mm (0.07 in)
Checking the valve
1Check the valve faceReplace if pitted or worn2Measure the valve margin thickness aReplace if out of specificationValve stem runout: 0.01 mm (0.0004 in)