Rubbing noise from engine backside

You trash the sprag springs that help keep the dogs engaged. Once the spring is stretched out the dogs will no longer engage and you're about to spend some money for the sprag replacement and that requires an engine pull and a couple special tools.

I know we are getting a bit off-topic, and the conversation is at this point academic. However, I too am having a hard time seeing how reverse rotation of the engine (by hand) could damage the sprag.

The dogs in the sprag are held between inner and outer races, which inherently limits their travel. So it would seem that the movement of the dogs would be the same regardless of whether you applied forward rotation form the starter or reverse rotation from the engine. Either way the dogs rotate slightly into a locked position and then movement of the dogs is arrested. So how does the spring get stretched more in reverse rotation when the relative movement of the parts is the same? 

I’m not advocating rotating the engine backwards; the Rotax operating manual says the engine should not be rotated in reverse.  I just can’t visualize how this can damage the starter sprag.  Maybe I’m missing something?

Trust us when we say this will cause damage along with prop kickback on startup. I've seen the stretched out sprag springs. A lot or owners have paid the price.