how do you remove the crankshaft from a 85 cc honda motorcycle engine

get ur dealer to do it, check the manual

Well if you told us all the model and year, we could find you the engine plan on how to do it.

Pretty much the same way as u do from every other motorcycle engine.

Remove the engine from the frame - not always neccessary.
Strip off the top end - cylinder head, cylinder & associated items.
Remove piston from con-rod.
Remove clutch, electrical generating system, primary drive & all associate items..
Split the crank cases & generally then lift the crankshaft out.

Guess if u r asking here then it would be best if u solicited some help, so u can learn with guidance.

Follow the other guys instructions and then have a flywheel pulley to take the flywheel off. Then Screw 3 bolts into the casings, push and turn onto the crank itself to pry the casings apart. The tool will look like a peace sign. Be careful not to strip them. As ur turning you need to tap on the casings with a rubber mallet.