Sorry India Four Two missed the ground adjustable cooling flap.
It would help if it could be modified so pilot adjustable in the air.
Then it could be closed at top of climb, when the throttle is closed slowly.
It might be a good exercise to move the cyl head temp probe around to actually see which is the hottest one and leave it there and leaning for max power might be a bad thing as reduces detonation margins and gives higher cyl head temps.
On 360s if operating at 65% power or less it generally OK to lean to rough and go rich just to stop it. But above 65% full rich is needed also operating at max EGT or on the rich side operating between Peak and up to 125F down of peak at full power is a danger area for engine damage at high power, best not to do it and keep it a bit richer for cooling.
I try to be a little clearer wrote it in a bit of a rush.
Carbed engines have poor mixture distribution across cylinders and trying to lean for max power above 65% of rated power can place some cylinders in the detonation danger zone.
Peek power is produced when EGT is 125F down on max temperature on the rich side of peek (does not matter what the actual temp is as at peek, as this can depend on egt probe location).
I think you will find Lycoming do not recommend leaning if the engine is above 65% power unless at high density altitude which automaticaly limits the output.
On injected engines mixture can better balanced and with each injector matched to it's cylinder (GAMA injectors) closer control of mixture control can be done with out cooking a cylinder. Also it is possible to run on the lean of peek EGT temps, 50f down at least and still have a smooth engine, but only at 65% power or less.
I think maybe leaning for max power on take off may have pushed your Nu 4 cylinder into the danger zone and the high cylinder temp and fast thermal cycling has caused the problem.
The 360 is always on the edge of failure, unless handled with care and as Lycoming state,
their engine is perfect it's bad operating procedures that break it not the design mistakes!!
Last edited by horizon flyer; 17th Jul 2015 at 14:48.