What size is my bottom bracket for a Nishiki Kinzua 29 Men's Mountain Bike

If you are replacing the bottom bracket, you'll need to measure the length of the axle. Usually its from 120mm to 127mm, depending on the how many chain sprockets on the crank. Measure from end to end of the axle and the chain line distance from the center of the frame to the inner sprocket. Most of the time you can just replace the bearings and it's good as new for under $10 in parts. A new sealed bearing BB assembly, can be purchased for under $15 on Amazon.

This Is FixYa, so I assume it's more DIY than take it to a bike shop and get over charged. There are lots of videos on Youtube to show you how to rebuild or replace a BB.

Hi if i remember correctly to size up for a bottom bracket, flip your bike upside down resting on handle bars and seat carefully not to damage anything, and where the bottom bracket go's through the frame of the bike you take a tape measure and measure the width of only the frame housing where the bottom bracket go's into this is a lot easier to do when the crank arms are removed. also on some bottom brackets when removed from the bike has all the data stamped on it depending on the type of bottom bracket. if not measure the width of the frame where the bottom bracket sits in too and that will be the size of the bottom bracket you need, then determine which type it is once you have remove the cranks arm which are attached to the bottom bracket could be splined drive or square tapered type bottom bracket basically the shape of the metal part that the crank arms push and bolt on to then match up on a cycle part website.