This is the scripting i use successfully on all helicopters, -except- the M-900:
_configEngineName = getText (configfile >> "CfgVehicles" >> typeOf _veh >> "HitPoints" >> "HitEngine" >> "name");
_configEngine1Name = getText (configfile >> "CfgVehicles" >> typeOf _veh >> "HitPoints" >> "HitEngine1" >> "name");
_configEngine2Name = getText (configfile >> "CfgVehicles" >> typeOf _veh >> "HitPoints" >> "HitEngine2" >> "name");
_configEngine3Name = getText (configfile >> "CfgVehicles" >> typeOf _veh >> "HitPoints" >> "HitEngine3" >> "name");
//the config names returned: 'engine_hit', 'engine_1_hit', etc...
_veh setHit [_configEngineName,1];
_veh setHit [_configEngine1Name,1];
_veh setHit [_configEngine2Name,1];
_veh setHit [_configEngine3Name,1];