Expert: Marc Ebelini - 9/6/2009

Question
Not too long ago, my dad's plane (a Cirrus SR22-GTSx G3 Turbo, if that helps) went in for its annual.  It turns out that he had a cracked intake valve.  Nobody knows the exact cause of this.  Do you know any major and/or possible causes of this?  Thank you.

Answer
There can be many reasons for a cracked valve. To determine the exact cause would require additional inspection. The prime suspect would be over heating. Fuel distribution is not always perfectly balanced for many reasons like compression, leaky intake etc. This will cause one cylinder to run hotter than others. Then of course air baffling is another. This explains why one cylinder; will run hotter. Then the valve it's self could be defective or the guides worn causing the valve to strike the seat unevenly eventually cause it to crack. Does your father's plane have an *EGT system to monitor each cylinder when leaning? Not knowing the instrumentation system on his plane I can only speculate. Some aircraft have a cylinder head temperature on only one cylinder that is assumed to be the hottest one.
May I ask if you have checked with the factory about the history of cracked valves on that model aircraft? No longer actively inspecting aircraft so I do not subscribe to the aircraft bulletins. The problem could also be rare so it has not made publication. *Exhaust Gas Temperature.