Grinding the valves to a feather edge is likely to cause which outcome?

Grinding the valves to a feather edge is likely to cause which outcome?

• A. Improved valve life
• B. Pre-ignition and burnt valves
• C. Reduced fuel consumption
• D. Lower engine temperature

Answer: (B)

Valves must shed heat and seal properly, which requires a gentle, radiused edge rather than a razor sharp one. Grinding to a feather edge leaves nearly no radius, making the edge extremely sharp. This concentrates heat at the edge and reduces the contact area with the valve seat, so heat isn’t transferred as effectively into the seat and cylinder head. The result is local hot spots at the valve edge during operation, which can ignite the mixture ahead of the spark (pre-ignition) and, with repeated heating, burn the valve edge and face. So, feather-edging the valves promotes pre-ignition and burnt valves. It won’t improve valve life or reduce engine temperature or fuel consumption; those outcomes depend on proper edge geometry and seating.

Valves must shed heat and seal properly, which requires a gentle, radiused edge rather than a razor sharp one. Grinding to a feather edge leaves nearly no radius, making the edge extremely sharp. This concentrates heat at the edge and reduces the contact area with the valve seat, so heat isn’t transferred as effectively into the seat and cylinder head. The result is local hot spots at the valve edge during operation, which can ignite the mixture ahead of the spark (pre-ignition) and, with repeated heating, burn the valve edge and face. So, feather-edging the valves promotes pre-ignition and burnt valves. It won’t improve valve life or reduce engine temperature or fuel consumption; those outcomes depend on proper edge geometry and seating.