ASE A1 Engine RepairCylinder Head and Valve TrainHard
A technician is performing a cylinder head overhaul and is checking the valve seats. They notice that the intake valve seat has a width of 0.050 inches (1.27 mm) and is located too high on the valve face, near the margin. The service manual specifies a seat width of 0.040-0.060 inches (1.02-1.52 mm) and contact in the middle of the valve face. Which adjustment is required to correct the seat position?
- ADecrease the angle of the bottom cutting stone.
- BUse a narrower 45-degree cutting stone.
- CIncrease the angle of the bottom cutting stone.
- DIncrease the angle of the top cutting stone.
Show answer & explanationAnswer & explanation
Correct answer: C. Increase the angle of the bottom cutting stone.
A high valve seat contact point indicates that the 45-degree sealing surface is too close to the margin of the valve. To lower the contact point, the bottom cutting stone (typically 60 or 70 degrees) needs to remove more material from the lower part of the seat, effectively moving the 45-degree seat closer to the center of the valve face.
Why the other options are wrong
- A. Decreasing the angle of the bottom cutting stone (e.g., from 60 to 50 degrees) would make it less aggressive, potentially moving the seat higher or making it wider, not lower it.
- B. Using a narrower 45-degree stone would only affect the seat width, not its position on the valve face.
- D. Increasing the top angle (e.g., 15 or 30 degrees) would widen the seat and move the top of the 45-degree angle further up, not lower the contact point.
Valve Seat Position Adjustment
Multi-angle valve seat cutting uses top, middle (45-degree), and bottom stones to achieve the correct seat width and position on the valve face for optimal sealing and heat transfer.
- Top stone (e.g., 30°) controls top of seat
- Bottom stone (e.g., 60°) controls bottom of seat
- Seat position affects sealing and heat transfer
Memory trick: Seat too high? Bottom stone's cry! Seat too low? Top stone's show!