A). . the BME series of engiens takes a 7/16 drill bit to match the prop alignment portion of the crank

B) Saying you will never own a BME due to this design feature is silly. I guess you would rather drill six imperfectly aligned (no matter what jig you use) 5mm (or so, since 5mm drill bits are VERY scarce) for your DA's.

C). . if you still want to maintain the original 10mm prop center hole, its very easy to use a partial depth hole in the propellor, which is just siffucient to slide the prop over the entire alignment part of the output shaft, and leave the rest of the prop hole at 10mm diameter. I have several props drilled with both the undercut for the BME, and the small 6-bolt pattern for the 3W 100 so that I could use the same prop on both engines. . no problems or issues. And if you are worried about centering a spinner, spacers are available from every spinner manufacturer to match whatever engine you are using .. and the outer diameter of the holes is 11mm/ 7/16" !!! BEFORE the spacers are inserted!


Hope this helps!