Quoting Removed, click Modern View to see
You can't eyeball it - measure it:
- When there is insufficient material on the head to grind in the proper width and angle of seat.
- When the valve stem is worn undersize. Before 8N-42161: .3105/3.115 (intake and exhaust) after 8N-42160: 3410/.3420 (intake), .3405/.3415 (exhaust). Wear limit .004 (intake) , .006 (exhaust)
- When guide to valve stem clearance exceeds .004 (intake) or .006 (exhaust).