How is valve seat sealing quality verified after overhaul?

How is valve seat sealing quality verified after overhaul?

• A. Perform compression/leak-down tests and verify seats hold compression; re-cut seats if leakage persists.
• B. Visual inspection of seats only.
• C. Replace valve seats as a standard step.
• D. Check for exhaust smoke signs.

Answer: (A)

Valve seat sealing quality after an overhaul is shown by proving the cylinder can hold pressure with the valve firmly closed. Start with a compression test to see that each cylinder reaches the specified compression and that readings are even across cylinders. If a cylinder won’t hold compression or shows a drop on repeated attempts, that indicates a seating issue. A leak-down test goes further by pressurizing the cylinder at top dead center with the valves closed and measuring how quickly air leaks out. If most of the leakage is through the valve seat, the seat isn’t sealing properly. If leakage persists, the seats are re-cut or reface to restore a true seal and then the test is repeated to confirm acceptable sealing. Visual inspection alone can miss microscopic seating defects, and simply replacing seats isn’t standard practice without evidence of leakage. Checking exhaust smoke signs is helpful for diagnosing other issues but doesn’t directly verify seat sealing after overhaul.

Valve seat sealing quality after an overhaul is shown by proving the cylinder can hold pressure with the valve firmly closed. Start with a compression test to see that each cylinder reaches the specified compression and that readings are even across cylinders. If a cylinder won’t hold compression or shows a drop on repeated attempts, that indicates a seating issue. A leak-down test goes further by pressurizing the cylinder at top dead center with the valves closed and measuring how quickly air leaks out. If most of the leakage is through the valve seat, the seat isn’t sealing properly. If leakage persists, the seats are re-cut or reface to restore a true seal and then the test is repeated to confirm acceptable sealing. Visual inspection alone can miss microscopic seating defects, and simply replacing seats isn’t standard practice without evidence of leakage. Checking exhaust smoke signs is helpful for diagnosing other issues but doesn’t directly verify seat sealing after overhaul.