nomad said:
Picture added of a near identical bike. (different colour)
The crank in the picture uses what is commonly referred to as an "American" BB -- also known more correctly as an ASHTABULA BB.
The Ashtabula BB shell is oversized compared with bikes which don't use an American BB.
An adapter which sleeves into the Ashtabula BB shell is available which will allow you to use a "standard" English BB -- the price varies between $20-to-$30, depending on where you buy it from.
You can buy a 110BCD "spider" which will fit on your bike's current crankarm + an individual chainring of your choice from any shop that sells BMX "stuff" ... or, go to
WWW.DANSCOMP.COM to see what is generally available in the BMX world.
Most BMX shops will also have individual chainwheels which will fit on your crankarm -- you will recognize the chainwheel because it will have a hole in the middle (for the axle) + a registration hole which the crank arm keys into.
Now, the fact that you either may not have paid much for your bike or your bike is old doesn't mean that it isn't worth spending money on it because whatever you put on it can be used on another bike in the future ...
Basically, only your budget and desire will limit you from updating components on the bike.
BTW. If you are moderately handy AND ambitious, you can replace the chainwheel, yourself.
I don't know what size bearings an American BB uses ...
The disassembly is pretty straight forward ... remove the pedal on the left side of the bike (I presume it has a left hand thread) ... remove the lockring on the non-drive side (bike tools are "needed" but I suppose a large pipe wrench could be used, but it would mar the edge ... remove the cup (again, a bike specific tool OR a large adjustable wrench if the outer surface has a raised 'hex' surface) ... snake the crankarm out of the BB shell ... replace the chainwheel ... clean and/or replace the bearings & repack with fresh grease ... reassemble.
You may have to remove the driveside cup in order to remove the crankarm ... I can't recall, but I'm currently under the impression tht it has to be removed, too.