Really open the crankcase for this?

Thanks for the reply. I am well aware of the implications of opening the crankcase. But this will incur not only many thousands of Euros for labour, but leaves me with an engine of 250 hrs with an opened crankcase and the risk of sub-optimal results and no flying this summer. 

Thus the search for ways to circumvent this design flaw.

What one could do is to heat the small sprocket wheel and pull it from the camshaft. Then it is easy to pull off the freewheel gear - that is straightforward. To press the small gear back onto the camshaft, it is not advisable to simply apply pressure to the camshaft in its installed state, that is, on the engine housing. However, it should be possible if one builds a frame that reaches around the engine block to the oil pump side at the other end of the camshaft, to press the gear (after heating it) back onto the camshaft with pressure applied only to the camshaft.

Has anyone ever done this before?

We know it has been done before, but it's not an easy or "approved" procedure and carries a high risk of causing serious damage. We cannot provide information on how to do it, but we will connect you with someone who has and may provide you with some insight.

Stand by for their response.

That would be very helpful and very kind, thank you in advance