Stof, I have built the 17.5cc single and found these faults with it, The shafts shown it the pics above are hardened shafts that I have used in other engines with no problems, the piston pins have teflon pads on either end, and the prop driver I was looking at using 4 or 6 bolt pattern, and I will machine up a set of locking nuts for the prop.
Cheers
Andrew
Cheers
Andrew