You could do this leak test before dismantling or just hold up to the light and look in the port, if you see light, you may have a bent valve. A good 3 angle valve job will have only 1mm contact area area on the head and if the machinist is really talented the contact point will be closer to the big end of the valve. The reason I was told not to grind valves and stems is the valves are Stellite Hardened and the hardening isn't very thick.