REFLECTOR: MT Prop failure mode?

[davedent at comcast.net]

Bernard, it just accord to me that you are  running a TIO-540 engine and not a TIO-550.  Has this engine ever run with a fixed pitch prop?  Remember the governor has to use pressure to maintain the 2700rpm.  So with no pressure it will stay at what ever the low stop is set at.  If the large piston on the prop fails you should see oil coming from the hub vent hole after a short time.

If the inner crank plug fails the prop can't build pressure up to maintain the desired pitch. The governor can build up 700 to 900 psi of pressure to move the prop. But with no pressure behind it, it has no supply pressure to it.  I don't think you have either problem. It looks like a plug in the intake system. Like something like a rag or bag got sucked into it.  Hard to explain how it could happen but I've seen worse.
  
I found a red rag left in a engine or two.  One left inside the crank when a prop was changed out.  Bad news for the guy that did it.  Another when one was left inside the prop.  It was a full feathering type, counting prop findings.  They never tried the feathering but when the prop came off we found the rag.  During the airline days, we found rags in places  you would never think they could get. After 49 years of doing maintenance on planes I thought I had seen it all but not true.  I'm anxious to see what you find.  

I talked to Jim Harp today at Thermal Mechanical Systems about it and he was the number one turbo man in the country for high altitude engines.  He's now retired at 86 years.  He worked with me on the NASA high altitude UAV's in the 90's.  He also thinks it's a plugged intake system.  With low MAP and high RPM it sounds like it.  

I must remind you also with low MAP and high RPM you can get into ring flutter real fast and damage you pistons.  At 2700rpm and less then 15 inches of MAP ring flutter can happen real fast.  You must maintain pressure on the back side of the rings to prevent scuffing and glazing. The flutter wipes out the ring grooves real fast.  So don't keep it there very long with less then 12 inches and that high of RPM.  

Keep on looking and let us know.  I know it will expand our horizons. 
Dave





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