09-11-2018, 08:57 AM
The seating area on an exhaust valve is quite hard, so the usual method of machining is with a valve grinding machine. Most companies who do re-boring crank grinding etc. will have a valve grinding machine. There needs to be enough margin (i.e. thickness) above the re-machined seat on the valve head to prevent the valve distorting in service. In other words if the seat of the valve would make a 45 degree sharp edge with the face of the valve once its machined it really needs to go in the bin.