2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 93Get this manual
Power unit Valve spring free length a: 53.20 mm (2.0945 in) 2Measure the valve spring tilt bReplace if above specification
6Remove the intake and exhaust valves
Valve spring tilt limit b: 2.6 mm (0.10 in) NOTE: Be sure to keep the valves, springs, and other parts in the order as they were removedValve spring compressor 8: YM-01253 Valve spring compressor attachment 9: YB-06320
Checking the valves
1Check the valve face for pitting or wearReplace if necessary2Measure the valve margin thickness aReplace if out of specification