Ok so I have an 0.s. 35 ax and when i start it with the electric starter the proppeller, spinner and the nut holding it to the engine comes unscrewed. The nut is fastened completely too.I can't figure it out. Is it something like the starter should spin clock wise or what i just can't figure it out.

While you say that the prop nut is completely fastened, butit is not. The cause of this is simply because you are not getting the nut tight enough when you install the prop. If you are using one of those 4-way wrenches that you use to remove the glow plug with, forget using it to install the prop nut. You can't get enough leverage with it. Get yourself a good box end wrench, and a good leather work glove to protect your hand with as you hold the prop( if you don't have a leather work glove you can hold the prop with a rag). As you hold the prop use the box end wrench to install the prop nut. Don't worry about getting it too tight as both the prop nut and the prop shaft are made out of steel and it's very unlikely that you will strip it out. Tighten is as tight as you can get it. Once you do this you will not have any problems with the prop coming off.

One other possible cause of the prop coming off when using an electric starter is you have primed the engine too much and it's getting a bit of hydraulic lock going on. But more than likely your cause is that the prop nut isn't tight enough.

Ken

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sounds like you dont have the nut tight enough. I had the same problem when I first got started, I didnt want to over tighten it but go ahead and crank down on it, it will be fine, you need to so it dont spin off like that.

Does your spinner have a plastic backplate? If so, these don't provide enough friction and the backplate will slip against either the prop or the prop driver which loosens the nut. Friction can be increased by making a washer out of a piece of wet/dry paper or very thin leather from gardening gloves. The best way though is to use an aluminium spinner. With enough friction between all the parts it's surprising how little the prop nut needs to be tightened. When the engine is running, the power impulses when it fires tries to tighten the nut.

This is not likely to be the problem since you have a spinner backplate but it is a possibility.
Be sure the nut is actually tightening against the prop and not against the non-threaded portion of the crankshsaft.

Prop nut ain't tight enough.
If you're going to tighten it like a girl, then tighten it like a big girl.

All the previous replies are right on the money.
However, be sure to turn the prop the opposite direction, before putting the electric starter to it.
This gives the electric starter a 'running' start at over-coming compression.

HTH,
EJ

http://www.rcuniverse.com/forum/m_70..._2/key_/tm.htm

Like others have stated, the prop nut must be very tight. There is another possibility(not certain if others have mentioned it yet): The engine comes with a hardened washer that is SUPPOSED to be under the prop nut and against the prop. If that hardened washer is installed on the other side of the prop (installed first, then the prop, then the nut) your problem will occur. I have seen this at the field a few times. The surface against which the back of the prop must bear against is very rough (a crosshatched surface like some metal files) and it is this roughness that digs into the prop and causes it to turn with the engine. This explanation may be difficult to follow, but it contains the information you need.

Is it coming off while you're starting it or just after? You could be getting a backfire which means the engine spins backwards. That can unscrew a prop nut.

try putting a nylon locking nut ahead of the propnut this will keep it from flying off

this occassionally happens to me when the engine is flooded. There will be too much resistance on compression and the electric starter will just serve to unscrew the nut. Once I remove the glow plug and drain excess fuel from the cylidner and exhaust, it's fine.

You have one correct answer and one maybe up there. As usual good ol' "downunder' has it right. OTOH if you have a thin prop hub as some props are, relative to the unthreaded portion of the crankshaft, where the prop-nut stops short of a tightened-down position, then all comes loose when you try to start. BTDT many times until many years ago, an old-timer of that time showed me the error of my ways. Use the sandpaper between the spinner back-plate and the thrust washer. Doesn't have to be pretty, just there. Aluminum backplates really need it and plastic backplates usually need it.

For 61 years I have tightened prop nuts with the Du-bro /Fox type 4-way wrenches. Never a problem. OTOH those that like to grunt can do as they wish. Personally, I never pursue undue effort relative to work. Of course certain large spinner nuts are too large and the small crescent type wrench is then my choice, as well as for gas-burners.

Wood props need to be check for tightness on a regular basis. By nature the wood "Gives" a bit leading to a condition other than acceptable tightness.

IMHO...NEVER use a Crescent wrench ( Slangly called a "Fitts-All" ) to tighten a prop! It's the wrong tool to use for a critical application.

Once you see how much you can really crank down on a prop, and, how much they actually need to be tightened...you will be good to go!

As far as the 4-Way wrench is concerned...if you can tighten the prop on my OS 160 with it...The drinks are on me, The arm wrestling match is over, YOU WIN!