ORIGINAL: Blazer1
I can tighten the prop nut VERY tight and it holds for a while but after a few flights I notice the prop has moved and is against the spinner. What could be the problem?
That sure sounds like you are using a single nut instead of a mandatory locking type double nut?
Big fourstrokes are notorious for that and only a collot type double nut arraingement will do. These engines are serious engines and not beginner types and they need to be used with serious accessories cheap plastic spinners espcially the type with plastic back plates are normally troublesome. I highly recomend something like a true turn for an engine of that caliber.
Here is an example of a true turn collet type double nutted adapter. Adapter refers to the fact this double nut has a threaded boss for a single 10-24 spinner bolt. The single bolt that hold the spinner on through a nose hole. This is the only type spinner I would ever recommend for that engine.
http://www.truturn.com/cgi-bin/store...3a&ppinc=adapt