If the bottom bracket is an older cup and cone style, remove the non-drive side crank. remove the left side adjustable cup lockring and bearing. Pick up a longer crank bolt. Install longer crank bolt in drive side bottom bracket spindle. With the left side BB cup removed you should be able to push the drive side crank so it sits against the right hand fixed cup. While holding the crank against the fixed cup give a few whacks to the long bolt with a hammer. Be careful not to hit the bolt on an angle and it should "push" the spindle from the crank. I have used this method many times over the years and it has yet to fail me. Only works with cup and cone b.b.'s tho.