I have a strange problem with my OS 46 LA engine that I've put in my Kyosho Trainer 40.
Its a nice engine and all...
BUT, for some strange reason the propeller nut keeps unscrewing itself!

Last time it did this in the air, at the start of a loop. I asked a friend of mine to try the plane and do some rolls and loops with it. He did a roll, a slow loops, got more speed and went for another loop.
When the plane was facing the sky we heard a strange noise from the engine, he aborted to loop and started to take it down when suddenly the engine started to scream!
We cut the engine and glided it down. When it finally landed we noticed that the engine was missing the drive nut, washers, prop nut, spinner and prop

I got replacement parts from the local hobbystore, the guy in the store didn't have parts in, but he removed them from a OS 46 LA in display, great service there
I got a new spinner and prop. I used something similar to Loctite on the prop nut this time. But it still unscrews itself every third start. But only 1/3 a turn this time, not completely. I've learned to hear when it gets loose but its still a very, very annoying and dangerous problem.

Anyone got a simple solution?

Most four strokes now come with a lock nut type setup. Try putting two nuts on the shaft. The second after you've already tightened the first. Hold the first nut with an open ended wrench and put the second in place and tighten against the first. If the flat sides of the nuts line up the second is not tight enough.

You might have your prop nut on backwards. Turn it around and screw it on the other way.

Matt

There are a few common causes for throwing the prop.

Running the engine lean in the air. The lean run can cause a bit of early detonation which losens the prop nut. Older 4-strokes had this happen all the time because they were easier to accidentaly set lean, and the lower RPM made it easier to backfire, but 2-strokes can do it too. Richen up your mixture a couple of clicks and it should go away.

If the engine is flooded and you use an electic starter, I've seen the starter cause a backfire that throws the prop.

Wooden props sometimes compress with time. You put the prop on nice and tight, and fly, but the wood slowly compresses, causing the prop nut to become loose. If you are using wood props, try something non-wood. Or be sure to check the nut once in a while.

Check and if you have enough prop thread length to add a split washer between the nut and the prop washer do so. We use the "red line" method to check for tightness. We grab the prop and tighten the nut until the force of the prop makes a red line in your hand. Then you know that its as tight as you can make it! I used to get loose props until I added the washer and tighened as above. I haven't had one come loose since.

only time I have experienced this is when i flooded the engine - but it happened on the ground with an electric starter just as described above. Any chance this is happening to you?
Photoniq
p.s. if you flood the engine one solution is to remove the glow and use the electric starter on the plane. Be warned, fuel will come shooting out of the glow plug hole

Thanks for the tips!
I'll look into them. What I did today was to clean it up better than the first time when I put on the Loctite, perhaps there was some fuel or whatnot on the axle.
I've checked for flooding, but no, no "fountain-effect"

Gonna check if I put the nut "backwards" cause it wasn't until today that I noticed that one end has some more roundness to it. Totally missed that before.
Might as well throw a washer in there as well