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A commercial fishing company contracted us to investigate the root cause of a failed marine vessel cylinder head. Fluctuations in exhaust pressure has been reported, and the valve seat has failed only 1000 hours after routine maintenance had been carried out on the engine.

Valve seats are the are the surface against which a valve rests, and they insure:

  • Effective compression ratio
  • Engine efficiency
  • Performance
  • Exhaust emissions
  • Engine life

Figure 1: A valve seat


In order to determine why the valve seat had failed, we had to look at all the elements in the engine that were affected by the valve seat failure.

In our investigation, we established that during the routine maintenance that had been carried out on the engine 1000 hours before the failure, the valve seats on the engine that failed had been replaced by non-OEM parts. We delved deeper into this to establish if this could have any way lead to the valve seat failure:

Methods of testing:

  • MICROSTRUCTURAL investigation
  • HARDNESS test
  • DIMENSIONAL evaluation


One Eighty’s methodology

Figure 2: Damaged cylinder head

Figure 3: Plastically overloaded and fractured valves


Microstructural analysis:

OEM valve seat:

  • OEM has no graphite in microstructure

Non-OEM valve seat:

  • Malleable iron is a cast ferrous metal
  • Initially produced as white cast iron
  • Heat treated to convert iron carbide to a nodular form of graphite called temper carbon



  • OEM valve seats were identified as high-alloyed white cast iron
  • Non-OEM Valve Seats identified as malleable iron

HARDNESS testing:

  • Results of both OEM and non-OEM valve seats were within AISI 12%Cr standards

DIMENSIONAL evaluation:

  • The non-OEM valve seat (in operation) provided the least interference
  • The non-OEM valve seat (new) provided insufficient interference
  • The OEM valve seat provided sufficient interference
  • Material defects were rules out as a cause of the failure
  • The hardness testing provided no abnormal indications
  • Insufficient interference was the cause of failure:
    • The dislodged valve seat prohibited the valve from closing
    • The piston slammed into the valves
    • The valves and pushrods bent
    • Debris in the combustion chamber resulted in extensive damage to the cylinder head
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