Prop Adaptor
 

Have a question about a graupner prop. I want to try a 12.5 x 7 3 blade prop on my 4 star 60 with a Magnum .91 FS in the nose. Only problem is the opening in the prop is 8mm and the crankshaft on the engine is 6mm I believe. Graupner sells adapters but I can't find a distributer that is not oversees. Can't bring myself to pay for that kind of shipping for such a small order. Any ideas? Tried Dave Brown and Tru-turn but they can't or won't make anything, which is understandable.

Thanks

Bueller?... Bueller?...

Go to your local hwd store and get a 6mmi/d bushing with the smallest o/d and bore the prop to match, but I would also geck the balance

Hope this helps

Cheers Bob T

APC electric props come with a few different adapter sleeves or you could throw some shrink tube on the prop shaft, you may have to go 2 or 3 layers but it does work well.

Good Idea. Do you think a brass bushing would hold up over time? Have to check if my prop reamer is even able to go any larger than 8mm. Thanks

Heat shrink! You only need to center the prop. One, two, or even three layers of heat shrink tube will build up your crank to the correct size. Do it all the time, and have for many years.

The heat shrink option never really occurred to me. Easy, and have all the tools I need to try it. Thanks!! Just as an afterthought, anyone tried that engine/prop combo? MAS 13x6 and 14x6 K props work OK with the Magnum .91. Honestly, just want to try it for the 3-blade prop cool factor. Can't imagine it will change performance much.

p.s. the shaft size is 5/16" not 6mm,, when you find a prop, use the SAE reamer or drill

For future reference, the hole does nothing but position the prop centered on the prop hub. 100% of the load is on the hub and back of the prop when everything is tightened down. You could have a 1/2 inch wide hole in your prop and wind up with a perfectly running setup if you got it centered properly before tightening it down.

as long as it doesn't shift,, having the right size shaft hole insures it doesn't shift,

Masking tape, electrical tape, etc.

I bought some plastic bushings from Mcmaster-Carr for this. I have many of these. PM me and i will send you some. I will try and find part number and post as well.

Chad

I've always use black electrical tape, no issues

It can't shift Scale once it's tightened down. If the prop is centered right and balanced, there are practically no side loads to make it shift. If you don't believe me, mount a prop with too big a hole onto an engine and torque down the bolt. Then see if you can get it to slide against the backplate. You might be able to make it shift if you put everything you've got into it, but there's no way it's going to move under normal operation.

I machine bushings up for spacers. A prop nut with a step is another method. It works well if the shaft is too short as well. Naturally you need a lathe for this. I use large fuel tubing or whatever for spacers sometimes. Heat shrink is more adjustable for size if you can remove it.

Thanks for the replies. Seems like I have a few options. As with most things I've learned in this hobby, a solution can usually found using a little creative thinking.

Some plastic spinners come with plastic spacers for adapting the spinner backplate to the engine crankshaft. Could work to adapt your prop to the shaft if you have any laying around.



Tom