What indicates valve seat recession and how is it corrected in overhaul?

What indicates valve seat recession and how is it corrected in overhaul?

• A. Cracked valve stem; replace the stem.
• B. Excessive timing chain slack; adjust tension.
• C. Pitting or recession in the seat; correct by re-cutting seats or installing new seats per specs.
• D. Camshaft wear; replace cam.

Answer: (C)

Valve seat recession shows up as pitting or wear in the seating area, which prevents the valve from sealing properly and building compression. In overhaul, you inspect the valve seats for recession, pitting, or loss of material. If recession is present, the fix is to restore the seat by re-cutting to the proper diameter and angle or by installing new seats (or inserts) per the engine manufacturer’s specifications. After restoring the seats, you re-seat and lap the valves to ensure an even, concentric contact and a good seal. Other issues aren’t indications of seat recession: a cracked valve stem points to stem integrity problems, not the seat; excessive timing chain slack affects valve timing rather than seating; camshaft wear changes valve actuation, but not the seated surface condition.

Valve seat recession shows up as pitting or wear in the seating area, which prevents the valve from sealing properly and building compression. In overhaul, you inspect the valve seats for recession, pitting, or loss of material. If recession is present, the fix is to restore the seat by re-cutting to the proper diameter and angle or by installing new seats (or inserts) per the engine manufacturer’s specifications. After restoring the seats, you re-seat and lap the valves to ensure an even, concentric contact and a good seal.

Other issues aren’t indications of seat recession: a cracked valve stem points to stem integrity problems, not the seat; excessive timing chain slack affects valve timing rather than seating; camshaft wear changes valve actuation, but not the seated surface condition.