Okay. I know that it is almost impossible to overtighten a prop. That being said, I am trying to tighten the prop nut on a APC prop with a cheap plastic spinner backplate. I know you have all seen this happen before, right before I get the nut tight enough, the plastic backplate starts to slip. The backplate has to align just right with the prop for an added degree of difficulty. What do you guys do? Maybe a thin rubber washer?

I have had the same thing happen to me too. Just after tightening it down, putting the tools away, grabbing the nosecone and try to screw it on with the screws and DOH! They don't line up! Geez... Get out the wrench, do it all over again, etc...

What I have found to work for me is to take it very slowly when tightening. Periodically I would check to make sure the nosecone is still aligned. When I get the nut reasonably tight using the 4 way wrench I get the boxed end wrench for the final tightening, again taking is slow. Also, when tightening with my right hand I would hold my left hand over the prop to keep it from moving.

Also, make sure your prop has been reamed out to fit over the shaft. You should not have to screw the prop on, it should slide over the shaft.

Good luck!

I've seen enough time wasted at the field with plastic spinners that I don't use them at all. On sport planes that don't need a spinner for looks, an aluminum spinner nut puts an end to the problem You can use your regular engine prop washer and nut, and the use the spinner nut as a jamb nut. Works great. Here are some examples:
http://www2.towerhobbies.com/cgi-bin...?&I=LXK241&P=C
http://www2.towerhobbies.com/cgi-bin...?&I=LXE159&P=C

Larry

One thing that will help. With a T bar sander sand the back of the APC prop. The back of these are never flat. This will not only true the back of the prop but rough it up so it can grab the spinner back plate.(you will be suprised how uneven they are)

David

Put a little round circle of sandpaper between the drivewasher and the spinner backplate.

Like LarryC I have gone completely away from the plastic spinners and am using the DuBro spinner nuts (the second link in his post) exclusively unless it's a plane that I use a TruTurn spinner on.

I've found that if I score a few grooves into the hub of the prop it gives it enought friction/bite against the spinner back plate to take care of that pain in the you know what problem.

I have the plastic backplate, tighten everything real tight put my starter on and spin the prop right off the engine. with this plastic spinner backplate there is only 2 threads left to put a jamb nut, that is not enough thread for the jamb nut is it?

rkliemann

When you say "jam nut" do you mean the second nut like on a Saito or the one and only nut like a 2C? If it is the one and only nut you don't have enough. I had a St 51 that was the same way. The crank was just to short. Some props are thinner than others you might look at that. Or just use a spinner nut. I have great luck with those.

David

I have the st .61 plastic backplate then prop then steel prop washer then the prop nut. only the one nut, the jamb nut would be a second nut of which there is only 2 threads left for that nut. I have another plane the engone does not use a spinner but has an aluminum spinner nut that goes on against the prop nut, maybe I will try this instead af the spinner, although the spinner looks nicer and I should be able to use it there seem to be plenty who use them. I'm new but I haven't heard this happen to anyone else.

thanks

rkliemann

Since the plastic spinners - in addition to the difficulties you are experiencing - are prone to breakage fairly easily and when they go the pieces go everywhere, I'd suggest going with one of the previously suggested aluminum spinner nuts, like the DuBro ones. To add to the safety issue mentioned, if you are having to crank down on the nut as hard and as tight as I get from your description, you may have already introduced cracks - even small enough that you can't see them - that will be promoting the previously mentioned destruction.

When dealing with spinners that are spinning around 12,000 RPM, I take safety over looks - and besides that, I like the look of the DuBro spinner nuts!

Like Jim says. Inexpensive, simple, but effective.

Deleted by poster

Just get an aluminum spinner. They look good, don't get scored up by the electric starter and you don't have the backplate problem.

If it has to be a certain color, they have anodized aluminum spinners, and as a last resort you can always paint it.

Something not commonly known about the plastic spinners is that in nose first crash the spinner may break and take the carburatror with it. I converted everything to the large aluminum nuts. They will last forever.

The fix is actually pretty simple. Use an external star washer between the spinner and the prop. As you tighten the prop nut the washer digs into the prop and into the spinner. This keeps them aligned as you apply the final torque. I used to have the same issue and fought trying to start out properly misaligned so that when it did slip during the final torque it was properly aligned.

I like Thumprding's solution. Never thought of that, but I have used the sandpaper disc trick with great success.