What is the purpose of valve lapping (grinding) during a cylinder head rebuild, and what tool is typically used to perform it?

1. To restore the mating seal between the valve face and the valve seat using a rubber suction-cup stick and abrasive lapping compound.
2. To straighten a bent valve stem using a hydraulic shop press and dial indicators.
3. To increase the valve spring tension by grinding the top of the valve guide.
4. To clean carbon off the intake port using a wire wheel attached to an electric drill.