Allison/RR 250-C20 Engine Coking
I have 3 OH58A+ helicopters with the C20 in them. Have had them different amounts of time. Our oldest ship we've had for about 15 years. Our newest ship we've had about 4 or 5 years. Starting to have engine coking problems. Already had the engine out on one to have the bearing replaced. Got so bad we couldn't spin the rotorblades by hand at all. Our newest ship is starting to stick lightly after being flown and then cooling down, and our oldest ship is doing the same thing.
We follow the 2 minute cool down religiously. Running mobil jet 2 engine oil.
Thoughts/recommendations?