Which statement is most likely true regarding mandatory valve replacement at overhaul?

Which statement is most likely true regarding mandatory valve replacement at overhaul?

• A. Both valves are mandatory replacement at overhaul.
• B. Only the intake valve is typically mandatory replacement at overhaul.
• C. Neither valve is mandatory replacement at overhaul.
• D. Only the exhaust valve is typically considered mandatory replacement at overhaul.

Answer: (D)

Exhaust valves face much harsher conditions than intake valves. They sit in the hot exhaust stream and experience higher temperatures, more aggressive thermal cycling, and greater seat erosion over time. Overhaul practices поэтому often mandate replacing exhaust valves to prevent leaks, loss of compression, or valve failure after many heat cycles. Intake valves stay cooler and suffer less thermal stress, so they are not typically required to be replaced at overhaul unless inspection reveals wear or damage. This combination—mandatory replacement of exhaust valves, with intake valves usually kept unless found defective—explains why the statement about replacing only the exhaust valve is the most accurate.

Exhaust valves face much harsher conditions than intake valves. They sit in the hot exhaust stream and experience higher temperatures, more aggressive thermal cycling, and greater seat erosion over time. Overhaul practices поэтому often mandate replacing exhaust valves to prevent leaks, loss of compression, or valve failure after many heat cycles. Intake valves stay cooler and suffer less thermal stress, so they are not typically required to be replaced at overhaul unless inspection reveals wear or damage. This combination—mandatory replacement of exhaust valves, with intake valves usually kept unless found defective—explains why the statement about replacing only the exhaust valve is the most accurate.