Building your own BMX bike from scratch can be a very rewarding experience. You will learn about your bike inside and out and be better prepared to make any repairs or adjustments you may need. You will need to research various BMX companies to find out the types of parts you will want to use. You can buy parts from any online company or your local bike shop. Take some time to research the different options and styles that are available so you can create a custom bike that will perform for your style.
Connect the BMX frame to the work stand. Lubricate the cups and secure the race onto the fork, gently using a rubber mallet to help force it in. Be careful not to mar the bearing surfaces. Grease your headset bearings. Place your lower headset on the base of your forks, and slide the forks through the head tube on your frame. Put the top bearings on the top of the fork then place the top cap on top of the bearings on the fork. Be sure to tighten the fork bearings to take out any play in the forks but also allow for them to rotate smoothly from side to side.
Attach the handlebars to the stem by unscrewing the top of the stem and placing the handlebars in. Screw the front plate back onto the stem. Grease the stem bolt and insert it into the forks and tighten stem bolt. You can spray liquid lubricant lightly onto the bar ends and slide on your brake levers and grips at this time.
Put in the bottom bracket by lubricating the crank tube of the frame and putting the bearings in. Attach the sprocket to the crank arm, crank, and spacer. Slide it through the bearings (you may need to hammer lightly). On the other side, put on the spacers and the second crank arm. Make sure you use the bolt in the crank to screw it all together, tightening the bolt on the sprocket firmly. Make sure you grease the cranks before screwing the pedals in.
Add the seat by putting the seat post into the seat tube. Be sure to use ample grease on both the seat post and tube when it is added to the frame. You can add your brake hardware at this time and run the cables from the handlebar grips to the back tires.
Install the front wheel into your fork dropouts and tighten the hardware. Slide your back wheel into the frame dropouts and loosely tighten hardware. Position your rear wheel until it is properly centred into the frame. You may need to add some additional washers to both sides of the wheel.
Tighten the chain by wedging a wrench between the bottom bracket and the wheel. Pushing against the bottom bracket will snug up the chain. Once the chain is properly tightened, securely tighten the bolts.
Put the seat on and finish your final fine-tuning and alignment of the front wheel and adjustments on the position of brakes, bars, stem and seat to meet your needs and taste.
To help your grips from wearing through, add nickels to the inside to act as bar ends. Grease the nuts and bolts to make them easier to remove if you have to do so at a later date.
Be sure to not over tighten and strip out your bolts--remember the old adage: Righty tighty, lefty loosey. Building a BMX bike correctly will take time. Don't try to rush the process--even experts usually need at least a couple of hours.