Ok folks,
I need a little technical advice. I have an OS 15 CV-A that I'm putting in my Herr Pitts build. Today I got the cowl ready and I held my engine up to the prop shaft hole and the carb catches on the back of the cowl vent slots before the drive hub protrudes completely. I was wondering if anyone has any suggestions as to how to extend the drive hub out a little further. Right now all I can come up with is stack a couple of nylon washers up to far enough to prevent interference with the back of the spinner. Any ideas?

Thanks- Mike