912ULS Noise Turning Prop

Thanks for responding Jeff. Is it OK to turn the prop backwards a little to see if the starter engages and makes the same noise?

It sounds like the noise is coming from the back of the engine. I'd pull the back plate off and check clearances back there.

Hi Jeff

If the sprag is coming apart it will not start.  The housing that retains the cams will slip too much if that were to happen and the starter will not generate enough RPM to excite the ignition to fire.  (slipping will drop RPM at the crank below the critical threshold of 225 to 250 RPM) This is checked very easily with a DC amp meter to read the draw of the power cable near the starter.  If it is less than 75 amp draw DC then it is slipping.  

Thanks for that info RW, I had not seen that test procedure.  That's a pretty severe noise, I think I would want to take a look under the back cover as Roger suggests. 

Off the point/general observation -  When our aircraft/machine "communicates" with us - odd noise/bit of a squeak/rattle/etc, it behoves the cautious pilot to investigate thoroughly - could  be a signal to an impending, minor to catastrophic, event.

I write from experience (an ignored rattle) - fortunately minour but could have been so much more.