How do you stop a nut from coming loose?

I just built a motorized bike and finished it today. i tried to push start it and there is a nut that connects the sprocket to the rest of the engine and when i let go of the clutch, the sprocket spins and causes the nut to come loose allowing the sprocket to spin freely. i need a way to keep the nut from spinning

I just built a motorized bike and finished it today. i tried to push start it and there is a nut that connects the sprocket to the rest of the engine and when i let go of the clutch, the sprocket spins and causes the nut to come loose allowing the sprocket to spin freely. i need a way to keep the nut from spinning and coming loose again.

Other answer:

19cbrown1:
On the engine sprocket where the nut is coming off….take off the sprocket and look at both sides of it and you will see a small drill hole offset the main sprocket hole. That should be on the outside. Next you have a tin washer with a crooked fingertip that fits over the sprocket and fits into the sprocket drill hole. Everything fits flat. So the next thing is the nut and you screw it on and the tin washer is larger than the nut so you flip up an edge of the tin washer so it rests against the nut.

One part of the washer is in the sprocket hole so it cannot move and the opposite side is lifted up so it rest against the nut. Now it never comes undone until you use a screwdriver and a hammer to flatten out the tin again to remove the nut.

You may have assembled it backwards by putting on the tin washer first(or left it out completely)

I worked on motorcycles but don't know the fancy names. Just remember procedure. It is a mechanical stop.(not Loctite chemical) and can be reused many times over.

fuzzy:
Something is missing from the assembly.(or you have put the motor output on the wrong side of the bike)
99% of threads are clocckwise tightening so you need the motor shaft turning ANTI clockwise or the load on the sprocket will make the nut unscrew. ie the chain drive should be on the LEFT side of the bike like 99% of motor cycles.
You also need a splined or keyed shaft with a matching sprocket. You cant rely on a tight nut alone to transmit the motor torque. Even with motor driving anticlockwise going forwards you will have any nut unscrewing on the over run. If all else is impossible you could try drilling right through the nut & sprocket horizontally & hammering in a roll pin. (I'd do that twice on opposite sides of the nut)
(Google "roll pin" t ofind out what I'm writing about)
Bertsta:
A sprocket nut should be fitted with a splined tab washer. The splines locate the washer on the output shaft and stop it spinning. Then when the nut is tightened up, fold up the tabs and they will prevent to nut from rotating… Buy a new one. They're a buck plus change.
Mark:
You probably don't have Locktite on hand, but superglue makes a good alternative.

Another good option, if there are enough threads left over, would be adding a jam nut. Which is just a second nut tightened up against the first, they lock eachother on better than you might expect.
https://en.wikipedia.org/wiki/Jam_nut

1graeman:
Get some of your mom's finger nail polish. Paint the threads and then put the nut on and tighten it down. Once the polish dries it will hold the nut in place.
Watson:
Use a left hand thread. Or secure the nut with a split pin.
STEPHEN:
Use a left hand thread. Or secure the nut with a split pin.
Alexander:
Loctite, nylocks, flange nylocks, the little nuts that have a shear pin run through them, etc. there are plenty of nuts and methods to prevent them from backing off.
Nomadd:
Locktite isn't going to do the job. You need to drill a hole in the shaft and use a castellated lock nut with a cotter pin.
Trevor:
There is a product called "Nut Lock " which you should be able to buy from most car shops.