been flying for two years and have about 600 hours in an r-44(500 hours of that is in a 2006 Raven II). No engine failures but will list the problems below. Didn't really think of any of them as emergencies but just a pain in the A**.
So many hydraulic leaks i lost count(few of them i landed and i couldn't see any fluid in the resevoir)
Alternator failure on the above r-44 with 30 hours on it
Fuel pump failure at night with 400 hours on it
Bird strike (bird hit the main rotor, dented the one blade then flew back(well flopped back) to hit the empenage and smacked down on that, the flying rat came about 1 foot from hitting the tail rotor(better day then it could have been, by the way i felt to big bumps one when it hit the blade and the second when it hit the tail fin and i mean big bumps).
Had the engine cough bad enough to where it lost power for a moment, dumped collective was looking to land then it stopped coughing.
I thought i would share the moment i landed in a park giving rides (i was cooling down) and a lady who was drunk and obviously on some drugs came running at the helicopter with her hands up. Needles to say my mom was working ground crew and she tackled her. I had my seatbelt off out of the aircraft running after her but my MOM beat me to it. I have to say after the fact i laughed pretty hard keep picturing my mom taking this lady down( some people have no brains but it is a good example to keep full situational awareness). That was probably the most scariest moment out of all the above.
In conclusion i'm always am prepared for the worst but i rather have small problems like above then having to deal with big problems. The above were obviously problems with the aircraft but i didn't list other problems found in inspections. I guess not all robbies are low maintenance.