jdkxtreme

Why does my prop come loose?When I put it on just like the book says.If I have to try to start this thing very much at all the prop comes loose.

Whirley Bird

My Feedback: (1)

Use a lock nut or tap the nut with a hammer a few times to deform one side.
But really if you tighten it go with a lock nut and get one of the nuts that have the nylon grip on the one side.
Make sure the engine isn't the cause of to much vibrations causing the nut to come loose

nothinbetr2do

it might be from it back firing, is it a new engine? when they're new the pinch at tdc can cause the engine to kick backwards. i've had engines start backwards. then all i do is give it some gas and it kills it self. so make sure your putting it together right and tighten the prop nut and give it another try

RCKen

My Feedback: (9)

Do not "tap the nut with a hammer". That's just tearing up perfectly good equipment. The problem is that you just simply aren't getting the nut tight enough. If you are using one of those 4-way wrenchs that most people use to take out glow plugs with you'll need to do this with it. Throw it away!! Well, keep it for the glow plugs but not for putting your prop nut on. Do to that find a box end wrench. Put the thrust washer on and then the nut. Use the box end wrench to tighten the nut. Use a rag or a globe to protect your hand while holding the prop as you tighten, and then get the nut just as tight as you possibly can. Don't worry about being too rough, both the nut and the shaft are made of steel and can take it. One other point, never EVER use Locktite on a prop nut.

Hope this helps

Ken

jdkxtreme

Am I putting it on correct?
I put the silver thing against the motor.then the back plastic backplate for the spinner to bolt to.then the prop then the washer then the nut then the spinner?

RCKen

My Feedback: (9)

Absolutely. That's exactly how it goes on.

Ken

downunder

The main reason props come loose when starting is plastic spinners. There's not enough friction against the prop (or the prop driver) to stop it from slipping and when the prop slips it loosens the prop nut. The friction can be increased by making some washers out of sanding paper or thin leather to go either side of the spinner backplate.

Another reason they come loose is the engine fires too soon (kicks back) and this loosens the prop nut. Firing too soon comes from using too much nitro, a plug that's glowing too hot (not heat range but from too much battery power) or too much prime. These things advance the ignition point.

With everything being correct, a prop nut doesn't need excessive force to hold the prop tight. I've used those 4 way wrenches successfully on quite large engines. What should be remembered is that any method used to start an engine (by hand, electric) is trying to loosen the nut but when running the engine itself is trying to tighten the nut unless it backfires while running.

Edit to add..
Oops...by the time I'd posted this I saw your post #5....plastic backplate .

bruce88123

Got to disagree with downunder. For a 2 stroke, 95% of the time the problem is that the nut simply wasn't tightened enough. Ken has the right idea. A good quality @8 inch box end wrench is the best way to tighten the nut. The crank and the nut are both tough enough to withstand the torque. Use the proper hardware as provided by the manufacturer.

Whirley Bird

My Feedback: (1)

Why not tap the nut and deform it a bit?
Some aircraft nuts are nothing but that.
Brand new then are made slight out of round so they go on tight.
What is the reason not to use lock tight?
Vegas/

da Rock

Why not deform the nut?
Because the reason for the problem really has little to do with the nut. As mentioned by more than one, if it's a 2C engine, he's just not getting the nut tight enough. And since he didn't mention a 2nd nut, it's probably a 2C engine. So why not deform the nut? No value if he tightens it enough. It's going on the prop shaft tight or going on loose isn't what's not holding the prop.

Why not use lock tight?
Don't need to hold the nut to the shaft. AND more importantly, don't want the nut locked tightly to the shaft while the nut and washer aren't compressing the prop to the backplate tightly enough.

Villa

Use a larger wrench and tighten the nut a little more. I gave up on the standard cross wrench we use and instead use a 10 inch adjustable since the nuts I use fit the started rubber insert.

bruce88123

When the nuts are made by the factory they are formed and THEN heat treated. You want to form them AFTER the heat treating which causes stress which could lead to cracking.

You don't use Loctite because it's a pain in the but to remove parts that have been assebled with it. Also some versions (many exist) are virtually unremovable.

Buy the part you need and use it in the manner it was designed to be used.

Scar

My Feedback: (3)

I have seen two different people with their prop coming loose for the same reason : They didn't ream the prop. In both cases, they were able to install the prop by winding it over the prop shaft like a nut.

The prop should slide over the prop shaft clear to the backplate or spinner backplate. Then, all the clamping force from the nut will be applied through the prop to the backplate. If the prop is not reamed, and has to be wound down the shaft, it will resist proper clamping.

Other props I have seen come off were due to lean backfire.

Just my 2¢ worth,
Dave Olson

anonymouse

WOW!! Deform the nut A good example of why to not stand in the rotation plane of the prop or in front of it...... Why not just take a pair of vise grips and deform the threads on the crankshaft????? and make it a locking nut ... [sm=omg_smile.gif] If tightend properly the prop shouldn't come loose....

bruce88123

I've seen a variety of aircraft bolts/screws with different types of anti-rotation/locking techniques either built in or applied but never intentional distortion of the threaded surfaces. On the nut side I have seen a variety also and distorted shapes is one method used. It works well in hot areas which would defeat many of the other methods such as nylon/plastic inserts and chemicals.

anonymouse

I guess I wasn't sarcastic enough...... You are right though, there are nuts that have a intentional skew in the threads for locking purposes and intentional mis-shaped areas.. Any intentional damage or mis-shaping to the manufactured design is asking for trouble..... If used as designed, there should not be a problem... I believe that you will destroy the prop before you can tighten the prop nut enough to damage the threads on either the nut of the prop shaft....... Interesting discussion though love those smileys

Whirley Bird

My Feedback: (1)

For your information I fly fixed wings and gyros.
I lost count of the number of the lock nuts that were sort of made out of round on one end and these are not heat treated nuts.
Isn't deformation the nut at the factory intentional?
It's called quenching.
I usually screw it on the threaded bolt except for the last three threads.
As for the Loc/Tight compound
They have the permeant type and the softer red colored type that can be dissolved with 20% R/C intro fuel.
To avoid a nut coming loose I use the deformed type purchased or made by me or the ones with the nylon collar and never had to use any chemicals on the threads to lock it up tight.
Anything wrong with rolling your own?
Vegas/

Whirley Bird

My Feedback: (1)

A 10 cent nut is considered equipment?
From what I read on other post the prop should be torque at 7-9 ft. Pounds so a nice small calibrated clicker wrench would be a handy tool.
Vegas/
Ken
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jmurphy18

Here is my perspective on this. I hold a Journeymans card as a jet engine mechanic and I am a Mechincal engineer with 20+ years experance. Bottom line is I am not shooting from the hip. I would have got fired or someone killed for buggering the shaft as you mentioned. That is not the proper way to do thing. Come on guys torque it as mentioned or get a nylon loc nut, blasted things are 10 cents! Use the blue loctite, 242 if memory serves me right. red tube blue in color.

Now if you hate someone.... use the black, permenant bond like we used in the lab. Hated that stuff

bruce88123

And "quenching" is part of the heat treating process when you place the hot part in a bath of water or oil to "quench" or cool it. Has nothing to do with deforming it.

Maybe you've lost count of the number of malformed nuts you've used because you are not using the proper parts. The nuts that come with my engines are all hardened steel. As I said before, buy and use the correct part in the correct manner.

anonymouse

Quench?.. Perhaps you mean clinch... Again I guess my sarcasm is misssed...I would never intentional bugger the threads on the shaft or in the nut.. There must be at least a dozen differen't manufactured locking nut designs for cold and hot applications. again like aforementiond if the nut is properly torqued the prop should not come loose.

anonymouse

John, Ever hear the term ""Hammer Mechanic" ? Being an aviation mech you must have met people whose motto is "If it won't go...force it." And "If you can't fix it...screw it up so bad no one else can."

bruce88123

"If it doesn't fit, you're using the wrong hammer".

scratchonly

Be sure your prop hole has enough clearance to fit over the smooth part of the crank and your prop nut is not bottoming on the threads before pressing on the prop.

carrellh

What is the "silver thing" that you are putting on first?

I'd expect to see:
Plastic spinner backplate
Prop
Washer
Nut
Spinner cone