u can grease and change them so that should answer your question
Main Journals
if you spun a main bearing then it is wise just to have the engine rebuilt.it is near impossible to fix mainbearing especially if it caused any damage to the crank shaft.
Floating bearings can move on the shaft fixed bearings cannot. If you search on Youtube for 'floating bearing animation' there is a short video showing the difference.
The big-end shells (connecting rod to crankshaft) and crank shaft journal bearings have failed.
You cannot fix a rod bearing. Bearings must be replaced. While it is possible to replace a single rod set, a bottom end overhaul might be the way to go. The rational here is that if one bearing is bad, how far off are the others? In addition, if crank shaft journal service is necessary, the machine shop will supply that correct bearing size after machining .
I would recommend that you do put a crank shaft head on a crank shaft. Putting any other type of head on a crank shaft could possibly break the head.
Crank shaft
If you mean ... why the crank won't turn when the key is on and the acc.'s will turn, Well sounds like crank shaft is locked up. When the crank bearings try to pile up on each other and jam the crankshaft in it's final resting place, till rebuild.
The engine crank shaft is inside the engine
The crank sensor on a 2001 Malibu is located on the bottom of the engine near the crank shaft. It monitors the rotation and speed of the crank shaft.
400 has a longer stroke
Where is the crank shaft sensor located in a Audi a6