Gang,

I don't have it here at work, but I believe John Schwaner wrote in his book "The Sky Ranch Engineering Manual" (a **very** good book on piston aircraft engines) that having the prop drive the engine was bad because it causes the piston rings to slap back and forth in their channels in the pistons.  This could lead to breakage of the rings.

BTW, I highly recommend this book to anyone that wants to know more about the "whys" of piston aircraft engines.  John's web site is: http://www.sacskyranch.com.

Regards,

Dan Olsen
320 MKII, 85%
Fort Collins, CO