Burping

NO IT IS NOT. 

ALTHOUGH MOST IF NOT ALL RADIAL ENGINES ARE DRY SUMP LIKE YOUR ROTAX, AN OIL TANK,  AS APPOSED TO AN OIL PAN BELOW THE ENGINE LIKE IN A CAR OR REGULAR LYCOMING OR CONTINENTAL ENGINE, THE OIL LEAKS INTO THE BOTTOM CYLINDERS WHICH COULD LEAD TO HYDRAULIC LOCK SINCE OIL IS NOT COMPRESSIBLE. 

YOU BURP ROTAX SO YOU CAN GET AN ACCURATE OIL LEVEL READING IN THE TANK BY PUTTING MOST OIL IN THE TANK. 

RADIAL ENGINES AS YOU KNOW HAVE BOTTOM CYLINDERS THAT GET FILLED WITH OIL AFTER SITTING DORMENT. SO, YOU HAVE TO ROTATE THE PROP AND THE OIL ESCAPES VIA THE EXHAUST VALVE INTO EXHAUST STACK AND OUT. IF THE PROP ON RADIAL ENGINE IS LOCKED UP YOU HAVE TO REMOVE BOTTOM SPARK PLUGS AND DRAIN THE OIL AND SOME ACTUALLY HAVE DRAIN VALVES. 

LONG STORY SHORT NO AND NO YOU DON'T GET HYDROLOCK IN ROTAX BUT BURP IT TO GET OIL INTO TANK SO YOU CAN GET ACCURATE READING ON DIP STICK. 

THERE ARE EXCELLENT EDUCATIONAL VEDIOS ON THIS FORUM REGARDING OIL CHANGE, CLEANING THE TANK, AND OIL LINES WHICH HAVE TO BE FOLLOWED CAREFULLY AND CORRECTLY. IF ONE REMOVES OIL LINES FROM THE TANK AND DOES NOT FOLLOW PROCEDURE, THE HYDRAULIC LIFTERS COULD BECOME DRAINED OF OIL AND THIS IS SOMEHOW REVERSE OF HYDRAULIC LOCK. BUT, PURPING BEFORE ENGINE START AND PREFLIGHT HAS NOTHING TO DO WITH IT AS EXPLAINED ABOVE. 

CHECK LOCKWOOD AVIATION TWO PART VEDIOS ON ROTAX FAMILIRIZATION ON UTUBE. GO TO UTUBE AND SEARCH LOCKWOOD AVIATION VEDIOS, FREE NO SIGN UP AND VERY VERY INFORMATIVE. WHEN IT COMES TO ADVISE, PARTS AND MAINTENANCE LOCKWOOD AVIATION IN FLORIDA IS AT THE TOP OF THE LIST.