Well no, you wouldn't want the prop out at the end of a 3" plus extension! As I said, I cut my shaft off to a more normal length and rethreaded it, and used a reasonable length prop adapter. I think most prop adapters run more or less 2" in length, and that is enough to have extended out there without a third bearing supporting things.

Just because it was right handy here, I just now measured my 48cc twin that I made. It is exactly 2" from the crankcase, (which is very close to the front bearing face), to the prop mounting surface. My 30cc Homelite is in that bracket as well....

BTW, even the cantilevered crank engines like the Homelites have two bearings. They have a big one inside near the crank web, and a smaller one in the nose of the crankcase housing. Even the "smaller one" is a good size bearing...

AV8TOR