I did about 3 searches and can't find anything on my question. Went out today and put my electric starter on the spinner to start it up. Off comes the backplate and spinner. Retightened nut, with some serious torque...same thing...doesn't make for a very safe situation. I'm thinking that it may have something to do with the way the prop is positioned on the backplate, but I could be mistaken. The instructions with my Tower Trainer say when putting the prop on the backplate, to rotate the prop counter-clockwise unitl it hits the SMALLEST pin. The problem is this APC prop won't fit between the larger and smaller pins which, as I see it, is the only way to have it against the smaller pin. The only way I can get it to work is to rotate the prop counter-clockwise til it's against the LARGER pin. As you can see from the pic, when I do that, the spinner doesn't line up.
Any help/suggestions would be greatly appreciated.

You mean the backplate, prop, and spinner cone came loose?

You've probably flooded your engine. When you hit it with the starter the engine won't turn over, or offers much higher than normal resistance, due the large amount of fuel hanging around in there. Result: the starter spins the prop off.

Try less prime. Better yet, have a go at hand starting.

To clear the fuel, take the glow plug off and spin the engine with the starter. Be warned: fuel will spray out of the glow plug hole when you do that.

Thanks. Do you think I'll run into any problems with the prop by tighting the spinner to the backplate as in the top photo?

Your first photo shows the prop in the correct position. You may want to switch to a different prop or a different spinner.

if it really wants to do that badly, try double-nuting it just to be safe. four strokes do that because they sometimes kick back when they start.

Thanks folks. Appreciate the feedback.

Hello F-16:

If all else fails get some BLUE Loctite from an auto parts store. Put a very small dab on the treads and install your nut. Do not use anything else, Red will stick that darn nut on permanently and any other will not have enough stick to help you. I also do not use regular nuts and washers on spinners. I use a Higly nut (saftey nut) and have vever had this problem. I wish you the best.

Mark Shuman

Looking at the picture, it looks to me that that spinner is way too small for the prop. What size spinner is it?

Try using at least a 2" spinner (if it's suitable for the plane). Most plastic spinners don't work well with APC props and need to have the slots widened due to the larger width of the blade at the hub.

If you can find one, try a SIG spinner, they have larger slots for the APC props.

When I changed from wood props to APC, I also changed to aluminium spinners as I was having the same problems as you. The spinner would come off, and it was a pain getting it lined up just right.

The only plastic spinner I've used with an APC was the spinner that came with my H9 Funtana, but I used it on a different plane with a smaller prop.

As threadlocker goes, I got mine from Lowes I think, it's Loctite Tite'n and it's blue.

I've heard elsewhere that you should never use threadlocker on prop bolts, and I would tend to agree.

When my engine threw the APC prop and spinner, the recommended solution was to just get rid of the spinner and turn the rubber starter cone around. This worked fine for me until I got a decent spinner. No loctite or special nuts requred...

Thanks. The spinner is the stock spinner. The slots in it will fit the APC prop, but I like the idea of going with the metal spinner. I was using a wooden prop that I initially bought with the plane, but when it came off the tip slightly split. I'm gonna put it together this morning and give it a whirl.

As well as a double nut, I use a nylock nut (the ones with a nylon insert that locks onto the thread, but are still reversible). My engine is a four stroker. Being new to this hobby, and having seen a prop come off a long time ago, I reckoned it was best to be really sure. I understand that with two strokes one nut is OK, but fourstrokes are different; lot of torque to resist the starter and wind the prop off with the electric starter.

the nylon nut won't really do anything. these engines have enough torque that all it does is sit there. you would have to tighten it up against the nuts like a locking nut. it can't hurt, but it doesn't really do any good.

Thanks again. I tightened it up, took the glow plug off and turned it with the starter....out came plenty of fuel. Worked fine after I put it back together. Got an hour or so of buddy-box time this afternoon.

whoa!!

Put VERY LITTLE!!!!!

I have blue loctite and when I put it on my servo monting screws and messed up, it would not come out until I got the electric drill and took it out on high torque. Luckily the mounting block did not get damaged.

I would also sand the back of that prop. Use a T bar or something flat. APC props are rarely flat on the back. I am talking about the center part that touches the spinner. This will also keep the prop from slipping while you tighten the nut.
David