Rotax 912 prop movement

Is the crankshaft turning? Take a look under the plastic Rotax cover on the back of the engine or remove the bolt where the locking bolt fits and see if the crank is rotating. If it is not, then there has got to be a fault in the gearbox.

Crankshaft was not turning.

Since found problem to be a fibre washer breaking in the gearbox. Chewed remains found in oil tank and in gearbox housing. Awaiting full inspection hoping not too much other damage done.

That fiber washer is called the thrust washer. It doesn't break very often, but it has on some long time installations where the gearbox doesn't ever get serviced or where there is a rough running engine for a long time.

The gearbox appears to have had its first gearbox service around 1300hrs, now 2000hr so that fits. There has been an intermittent vibration around the 3000rpm revs when coming off the power, lightly jabbing the power a few times bringing it back to 3000revs (desending), would smooth it out. My weigthshift cruises at 4100rpm, which I understand also adds to gearbox strain.

One other recent change (last 5/10hrs), number 3 EGT shows it decreases temp a lot quicker and further than the other 3 EGTs descending power-back 2000ft... Powering back up, the temp would increase faster and go higher than the others. Setting a constant cruise, they could all be the same/similar....Checked the plugs and all look good/similar... anyway thats another problem I guess for when/if the gearbox is fixable.