Bottom Bracket for kids bicycle
 

Hello

I bought a bicycle for my kid from an online store and everything was ok until I found out that it's bottom bracket bearings are open and not sealed. mud from wheels get into them and they give some squeaky noise. I'm thinking of changing the whole bottom bracket set but I'm not able to understand what type of bottom bracket it is. I would be sharing few pics of the bicycle. Please can any one help me what can be done. what type of bottom bracket can be fit to this bicycle?

Without knowing what the make / model of the bike is, we can't really tell what kind of bottom bracket it has.
Most kid's bikes have what's called a 1-piece crank, where the crank arms and spindle are a single, Z-shaped piece of steel.
This type does use a large nut on either side of the BB to retain an open-cage ball bearing.
Bad news, is that this type is not 'sealed' and water and dirt can get in. It also doesn't have much grease in it from the factory.
Good news, you can easily open up one of these type BB with a large adjustable wrench, clean all the old grease out, and repack it. I use what's called Marine Grease. It's intended for boat trailer wheels. It's cheap, waterproof, and can be found at pretty much any auto parts or hardware store. One good repack is probably all that bike will ever need.

Just remember that when you are opening up an Astabula, or one piece crank set, it is easier with the pedals off. Also, the locking nut and the adjustable cones are LEFT HAND THREADED (reverse) on the non drive side.

If this is your first time taking a bottom bracket apart, I would recommend that you take a lot of pictures with your cellphone each step of the way so that you can see how everything fits together.

What you said is true. since i'm a new member here, I can't post the pics which I have taken to share it here. the problem here is the fame is also open so mud enters from that open area easily and the open bearings are filled with mud giving loud noises. even if I take it out and clean and overhaul with marine grease, the next day the mud will be filled into it. do we have any remedy to seal the bearings?

Can you post your pictures to hosting site like flicker, Google Photos, etc.? That would make it easier to determine your options.

As mentioned above there are two broad possibilities: a one-piece (aka "Ashtabula") crank, with pressed in races, and a threaded, "cup & cone" type bottom bracket. Ashtabula units are easy to service, if you keep in mind that the adjustable cone and locknut are left hand thread.

Plastic sleeves to protect bearings in a threaded bottom bracket are readily available, e.g.:

http://www.os2.dhs.org/~john/sugino-sleeve.jpg

A threaded cup & cone type bottom bracket can be replaced with a sealed cartridge unit, provided you can suss out the proper axle type and length. And there are conversion kits to install a threaded cartridge unit into a frame designed for an Ashtabula crank.

But again, pictures of what you have would be a great help.

https://cimg3.ibsrv.net/gimg/bikefor...7f387908cd.jpg
https://cimg1.ibsrv.net/gimg/bikefor...c7580cb369.jpg
https://cimg8.ibsrv.net/gimg/bikefor...edac1353ac.jpg
Thanks everyone. I have opened it up just as you all have given instructions and it came out with some difficulty as the new paint was hindering the movement in the bicycle axle but rest all came very easily. Thanks for your guesses without seeing the pic. this is the first time I'm able to post pics and it's exactly as you have mentioned. this single piece mechanism is very easy to clean.. To counter the gap in the frame at the bottom bracket where the mud enters I took a medicine bottle made up of plastic and cut it accordingly and inserted it. I had another trouble while doing that - A protruding piece of metal is welded inside the bottom bracket so that you can't install any other bottom bracket and for that I made an opening in the plastic to let in that protruding part.

Thanks all. Now there won't be any maintenance atleast for a while