Gear Box with no friction Torque

I assume you discovered this while burping engine to check oil.

I suspect you might have a stuck valve possibly intake on at least one cylinder. Too late to use TCP NOW SINCE IT IS A PREVENTATIVE MEASURE. I USE TCP ALWAYS SINCE I RUN 100LL.

REMOVE VALVE COVERS ROTATE PROP AND SEE IF ALL VALVES  WORKING OK. IF WORKING OK DO BORE SCOPE INSPECTION TO MAKE SURE YOU DON'T HAVE A BURNED VALVE. IF ALL OK GO AROUND PATTERN FULL POWER, LAND AND SEE IF YOU GOT RID OF CARBON DEPOSIT ON THE VALVE.

NOW IF YOU HAVE A STUCK VALVE DUE TO LEAD DEPOSIT ON VALVE GUIDE AND STEM AND COAKING, CARBON, IT must BE REMOVED. IT IS POSSIBLE TO DO IT WITHOUT REMOVING CYLINDER BUT VERY TRICKY UNLESS YOU DONE IT BEFORE.  

IN PAST REPLY I STATED POSSIBLE INTAKE VALVE STUCK. I MEANT TO SAY EXHGUST VALVE. USUALLY EXGHUST VALVE GET STUCK OPEN SINCE ITS MORE SUSEPTIBLE TO LEAD DEPOSIT AND CARBON DUE TO HEAT. NOW ROTAX ENGINE CLINDERS RUN MUCH COOLER THAN SAY OTHER AIRRAFT ENGINES LIKE LYCOMING BECAUSE ROTAX HEADS ARE WATER COOLED ALSO. THIS IS VERY BAD AND YOU MUST USE TCP OR OTHER TO SCAVANGE LEAD. IF YOU DON'T GET CYLINDER HEADS HOT ENOUGH LEAD WILL NOT GET SCAVANGED. 100LL IS DESIGNED TO GET RID OF LEAD DEPOSIT ONLY IF CYLINDERS GET HOT ENOUGH OR IT WANT GET OUT OF EXGHUST. 

ALSO, DON'T USE FULL SYNTATIC OIL. 100LL AND FULL SYNTATIC OIL DON'T GET ALONG. YOU CAN USE THE AEROSHELL OIL FOR ROTAX. BUT, PENSOIL 10W40 MOTORCYCE OIL WHICH IS FULLY MINIRAL OIL FOR WET CLUTCHES IS BETTER. DO CHANGE THE OIL FILTER MORE OFTEN MAX 25 HOURS AND CLEAN THE TANK WITHOUT PURGE. THERE ARE VIDOES SHOWING HOW TO CLEAN TANK WITHOUT PURGING. OIL IS CHEAP COMPARED TO OTHER ISSUES. 

HOPEFULLY YOU JUST HAVE SMALL CARBON DEPOSIT ON VALVE SEAT. IF YOU ARE PRODUSING GOOD STATIC RPM BEFORE TAKEOFF GO FLY IT FULL POWER GET IT HOT AND YOU MIGHT SOLVE YOUR PROBLEM.

GOOD LUCK AND AS ALWAYS SAFETY FIRST AS PILOT IN COMMAND. 

Very soon I will dismentl the Engine and update all friends.

The propeller power was very week.

I have checked the compression level at all 4cylinders. As attached line maintenance manual 5.1 .

The cylinder no 2 dropped the pressure below permissible pressure.

What to do next?

First run the engine for a few minutes and do a compression check again on the weak cylinder. Many times this corrects itself.