More on Hi CHTs in R44 with EDM830
The problem we had with the engine failure was definitely inlet valves. However when the other cylinders were inspected they found issues with excessive clearance in exhaust vales. What I omitted to mention was that for the first 73 hours the R44 was (a) hard to start, and (b) always built up a black soot in the exhaust pipe and rear panel of the heli. The carby was re-worked for the starting problem, but from then on the tailpipe was light grey color, and no black build-up on rear panel.
However when we inspected the ports after the engine failure there was a lot of 'soot' in the ports. I believe that this was the original cause of the problem, carbon deposits building up in the ports and on the valves and the high CHT temps baking the carbon so eventually it caused breakdown and failure at the inlet valve sealing surface.
Lycoming want high MAPs for run-in, but this involves higher temperatures than their spec. Following is a sample from 2.2 hr flight in December 2011. MAP 23.3, Cyl 1 459deg F, Cyl 2 405, Cyl 3 453, Cyl 4 454, Cyl 5 458, Cyl 6 430.
The Lycoming manual specs 435 deg F as max long life, but if you fly Cyl 2 for max of 435, the MAP will be too-low for their run-in, and too-low for normal Heli ops. I plan to test this tomorrow 5Feb12.