the condition of the seat is not a important as the valves themselves. any ridge or groove in the valve is cause for discarding for the intakes ,the exhausts can be re cut then a light lapping to check that the seal is good is all.
O.E.M. Has suggested that a vigorous lapping to renew the seal is ok. My point of view is from a racers perspective that power production is tantamount. not simply 'RUNS OK"
A good valve job allows the valve seat to start flowing as soon as the valve breaks the seal as little as .001" any grooving on the valve can increase this amount to .01' or more. this can translate to a reduction of valve opening time and height. coupled with a too large a clearance setting can result in a massive loss of power. but it will "RUN OK".
Also on the valve itself, the area above and below the seal line can and does affect the flow too. keeping the valve clean and if allowed removing as much of the unsued portion can aide power production.
The sealing surface is critical for sure ,but the angles under and over the sealing surface are where the power is made. This is so important that stock racing rules prohibit anything but stock 3 angle valve seat cutting.
On my race bike engine ai redid the valves after every race to refresh the seats.
I submit the above for you entertainment and enlightenment not to say it is necessary
I hate PMs if you want to contact me, find my email address.
Last edited by fog; 2-2-2017 at 6:39 PM.