Cranks…

1-piece…

Put your cups in the bottom bracket. Put your sprocket and your spanner nut on your crank.  Grease up your bearings, and slide the crank through.  Slide all of the remaining parts onto the other side.  Tighten the inner nut, then tighten the lock-nut (outer-nut) onto it.  Grease up the threads on your pedals and screw them in.

3-Piece…

Put your cups in the bottom bracket.  Slide in your spindle.  Put your sprocket and your spacers on the ends of the spindle.  Grease the spindle and slide the arms on.  Tighten them with the bolts on the ends.  Grease up the threads on your pedals and screw them in.

Why won’t it loosen?

Hint:  All the threads on the non-sprocket side of the crank are left-handed threads.  You have to turn them to the left to tighten, and to the right to loosen.  This goes for the pedal on the non-sprocket side as well.

Also…

The measurement number on the side of the crank is the length of the arms.

Three piece cranks are much stronger than one pieces. You may not be able to feel it but a one piece flexes a lot. It can really affect your riding if you are used to a stiff crank. I’m not saying that your riding will get better if you get a three piece.

They are stronger and last a lot longer.