If the prop comes loose when starting then it's a lack of friction somewhere. A hard plastic prop like an APC has very little friction against a plastic backplate surface for instance. Something has to give and in your case it's the prop stud instead of the more usual nut. The prop stud like the Norvel uses is an excellent idea and all engines should have that instead of the usual one piece crankshaft because in a crash the stud breaks instead of the crankshaft. Some other engines also use that system, some K&B's, Taipan etc. If you take out the stud you'll see there's a different length thread at each end. This is to allow for prop hub thickness from fine pitch to coarse pitch props so if you locktite it in place you're likely to lose that benefit and if the stud breaks you may not be able to get it out. Also, if you locktite it then you'll still have the problem of the prop coming loose but then it'll be the nut. I really like the captive prop washer on the nut too and I don't know of any other engine using that.