Re: How do I change one piece crank to 3 piece crank?
Just today I had the same problem, needed to change an old one piece crank to a wider 3 piece crank that will clear the motor on a West Coast Chopper Bike.
I took a long bottom bracket shaft from the loose ball set up and machined it for 5/8" I.D. sealed bearings. They are pretty tough so I had to use Ceramic tooling.
Then I removed the bearing cups for the original bearings and machined bearing caps from 6061 aluminum to support the sealed bearings. Worked out pretty slick.