Why does my prop nut keep coming loose?

---------------

If you are using a spinner with a plastic backplate, there really isn't much you can do except retighten it periodically before you lose the whole assembly. This is why metal backplate spinners exist, to eliminate this same problem.

Ed Cregger

---------------

If you are using a spinner with a plastic backplate, there really isn't much you can do except retighten it periodically before you lose the whole assembly. This is why metal backplate spinners exist, to eliminate this same problem.

Ed Cregger

Or used thread locker, a nylock nut, or any other number of classical methods of stopping nuts coming loose on shafts....

Alternate would be to use a second prop nut that acts as a torque- lock.

Does sound like you're getting kick-back or are using the wrong technique for starting the engine.

What type of chicken-stick are you using? Are you back-flipping or flipping in the direction of normal rotation? Are you smakcing the prop or flipping it? Are you using the stick with the left or right hand?

The usual setup that I've used is that the prop is horizontal when rotated back against compression (i.e., engine stops in flight and the prop is horizontal.) Assumption is that hand-propping or use of the chicken-stick is with the left hand.

This puts max compression somewhere around the 11 o-clock postion.

Chicken stick is placed against prop with it in the horizontal position and then moved briskly up and to the right so that the full arm movement takes the chicken stick across the engine's face and away from the front of the engine. Slightly exagerated, you're throwing the chicken stick over your right shoulder.

Same works for hand-propping -- fingers are resting on the front of the propellor's surface and you're flipping up and to the right from the start of compression. Again, make sure that your hand exits the prop arc by pretty well throwing your hand over the oppistite shoulder. Props bite HARD! Never grab the prop and flip it taht way with the glow lead connected.

Harry, also make sure you have a wrench that fits. If your are afraid to round off the flats of your prop nut you may not be getting it tight enough. I bought the prop wrench that is flat metal with cut-outs for many prop sizes and it works well (except on nuts that have been misshapen by a crescent wrench). I haven't cracked a prop by over tightening yet. mk

AH..

uh...

MY engines must be special because they all turn counter clockwise..i.e. from right to left.

The method *I* use differs from 2 stroke to 4 stroke.

On two strokes, I put the prop up against compression around 1 to 2 o'clock before I tighten the nut. Then I move the chicken stick briskly from right to left, just as byrocat says but not in his direction.

Four strokes have different requirements and are treated differently. I install the prop so that when it is turn BACK against compression it is at about the 3/9 o'clock location, then I tighten the prop nut. After getting the carb real wet, I back the prop up to compression, heat the glow plug, and hit the prop in the reverse manner (from high to low on the RIGHT side of the prop disk as you face it). The trick is to cause the fuel mix to fire and throw the prop around in the correct direction fast enough to repeat the performance on its own. Sometimes on some engines I get a good reverse run and have to start over.

Try using a nylon prop instead of wood. And don't run your engine too lean. Also if you flood it during starting it could kick back and loosen the nut.

Er... You do have the aluminum spinner backplate behind the prop don't you? Also a thrust washer in front of the prop between the prop and propnut? Is the engine back firing or flooded maybe? A second nut jammed onto the first one is also a good idea.

Maybe you are heating the plug too much? If you do, the risk of pre-ignition increases, and sometimes the engine will ignite early enough to kick into reverse.

The plug should glow red or dim orange. Bright orange or yellow is too much.

I see that Bellsouth is double posting again.

Ed Cregger

Ed Cregger wrote:

What Ed said. I hate plastic spinners and have had that same problem. My father has an LT40 with an OS .40FX (or LA, I forget which) that would loosen while starting at least once every flight. I either use metal spinners or forego the spinner completely and use a propnut or acorn nut as they are sometimes called. Never had one of those come loose. I do use a metal spinner on fast planes such as my Super Sportster 20 or Kaos where you want to minimize wind resistance. The propnuts go on my fun fliers such as an Uproar or Ultra Stick.

I've been using all-plastic spinners since I started in 1990, and I have never had a propeller come loose except once. The one time it happened was on a Saito 91. The engine backfired and the prop spun loose.

I theorized that that problem had been caused by congealed oil in the needle valve restricting fuel flow on the first flight of the day, leaning the mixture. The cure was to run the engine at idle for a minute or so before running it up, which prevented further occurrences.

Anyway, no problems with plastic spinners here.

Fubar of The HillPe> What Ed said.

"Fubar of The HillPeople" wrote

------------

I'm a big fan of AMA safety nuts and I too fly them on everything that will look okay with one on the nose. Ditto metal spinners for those models that just have to have a spinner.

Ed Cregger

I have a long time friend that can use plastic spinners and get away with it, like you. But I'll be darned if I can.

Ed Cregger

11 o'click!?? You must be left handed? I always set compression at 2 o'clock. If you're right handed and set it at 11 o'clock you're gonna get whacked!

--------------

Oops! The old peeps aren't what they used to be.

In that case, honker down on that wrench. Works for me.

Ed Cregger

--------------

Oops! The old peeps aren't what they used to be.

In that case, honker down on that wrench. Works for me.

Ed Cregger

Every ounce in a while an engine will slip though the inspection at the factory,most of the time what you explain happens on plain bearing engines, A club memebr had one like that, and no matter how much running in we did it saatill stopped after less then a minute in the air. The biggest reason for that was that the piston was not fitted to the sleeve and as the engine got hot it would stop.I can't remember how many gallons of fuel was used, One thing was done the engine was returned to the manufacturer and they agreed that it was one that hasd slipped by, and replaced it. Plain bearing engines are not sometimes of the fit of the piston to sleeve. no matter how carefull the maker is. If after some carefull bench running of a few minutes, and the exhaust oil is BLACK, shut it down immediately, and let it COOL down, repeat as needed to clear that oil to a ligh to medium brown,and DON'T pesist in trying to run it if the exhaust is black to dark brown, Ray