Check for Play in a 2 Stroke Crank Without Dismantling the Engine

A quick way to tell if the bearings are definitely shot.Not foolproof but worth doing anyway.

Steps

Warm up the engine.
Switch off the engine.
Remove the engine cover that the generator/alternator sits behind.
Grab hold of the generator/alternator and very firmly try to move it up and down and front to back.
Feel for any slight movement or clicking in the generator.
If you feel any then the crank needs a re-build since the generator is bolted to the end of the crank

Using a dial indicator and comparing reading changes with manual specified end float and radial movement tolerances will give a more accurate idea of the significance of any play found.
Get someone to hold the bike while you are trying to move the generator.
You Must use a dial indicator, if you have reached the point where you can easily feel the radial movement by hand, the crank and/or the main bearings are stuffed and the engine would be running very rough and hard to start. As a general rule only, if the movement is greater than .004" to .006" the seal won't be flexible enough and will start leaking and allow either air or transmission oil to be sucked in, and your mates will easily follow you with the smoke trail.
To perform the test correctly you need to remove the alternator/flywheel and use the dial indicator direct onto the shaft, and on the other end the primary chain or gear must be disconnected from the clutch or removed.

If there is no movement it doesn't mean the crank is healthy,just that it's not really worn.
This is more a test to see if the crank is bad rather than a test to see if it's good.