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

That should work if you have enough shaft to get the nut on after the shimming. I might use aluminum washers if it was mine. What ever you use, try to use just one of the right thickness so you do not get spinning between washers. You will need something to keep the prop from spinning on the nylon washers. Perhaps some 30-80 grit sandpaper disk material glued to the nylon washer. Make sure that everything is balanced extremely well as the farther you get from the prop hub, the more a slightly out of balance prop will tear apart the engine.


I have a lathe and built a 3/4" spacer for my Magnum .52 xls. I had to turn a special nut that fits inside the prop so that I could tighten it without having to add an extension to the shaft. I balanced the prop and nosecone together as a unit. It runs without excessive vibration.