My Pulse XT 60 w/ Saito 100 has a 2 1/4" plastic spinner that does not want to tighten enough to hold the prop. I had to cut the spinner a lot in order for the 14x8 APC prop to fit but I would not think this would cause it to slip? I reamed both the prop and the spinner back plate to 8mm and the fit the shaft fine. 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?