Inspection And Maintenance Required After An Overload Clutch Slipping Event

The Rotax folks have published a Service Bulletin after issues were noted that affect all R915i and R916i series engines. 

Rotax operators have reported occasional, isolated, cases a momentary slipping of the overload clutch -- which may lead to a slight exceedance of the maximum rpm limit, followed by the engine rpm quickly normalizing. 

Rotax describes the overspeed event whereby the engine speed setting is actually between 5500 rpm and 5800 rpm at WOT stabilized, 'followed by a sudden overspeed up to 6500 rpm for less than a second. The clutch increases its transmittable torque during slipping condition and synchronizes the engine speed with the propeller again, which consequently lead to an undercut of the engine speed down to 4000 rpm followed by a recovery of the initial engine setting between 5500 rpm and 5800 rpm. 

The entire event is lasting up to 3 seconds. In rare cases, if upper sequence happened more times unidentified, the transmittable torque of the overload clutch will be reduced and the speed fluctuation just can be stabilized by a slight reduction of the throttle down to 96%. If the engine speed has stabilized the throttle setting could be increased to WOT again.' 

SB-916 i-003/SB-915 i-014 describes the problems that may be encountered and the remedial applications that may be applied including the possible removal and replacement of a new overload clutch assembly and the instllation of a matching new drive gear. 

FMI: https://legacy.rotaxowner.com/si_tb_info/serviceb/SB-916_i-003_915i-014.pdf