Hi all...
Please help me understand how to identify and to measure the crank stroke of a crank that is not installed in a motor. Also there is no markings on crank.

That appears to be a CY full circle stuffed crank. An easy way to tell the stroke is to use a caliper to measure from the edge of the rod big end pin ( nearest the shaft ) to the edge of the shaft diameter ( not on any radius at the counterweight ). If that measures .120", that is a stock 28mm. stroke. If it measures .140", that is +1mm ( 29 mm. ) stroke. If it measures .160", that is +2mm ( 30mm. ) stroke. These measurements are very close approximations, as it's difficult to tell the exact edge of the rod pin. The metric measurement would be 3, 3.5, and 4mm respectively.

Can you explain this a little better I'm trying to figure the stroke of a tiger king crank I have that is either 28.6mm or 28.8mm , in my 290 with stock base gasket I have 15 thousandths . I don't think the crank is 28.6mm stroke

Using a dial caliper, measure from the outside of the shaft ( nearest the rod ) to the center point of the rod pin, and add 6mm ( half the shaft diameter = .2362" ). Take that total and multiply by 2. That is your stroke. "Inches" is more accurate, and can be converted to mm.

You are never going to measure using this method to tell a 28.6mm crank from a 28.8mm crank nor is there a easy way other than putting it in a case with a cylinder on it and measure the stroke.

No disrespect to you Dan, but if a guy is going to fool around with cranks that are produced within .008" total stroke of each other and may not be clearly marked as such, JMO but he needs his head examined. It almost seems that some of those TK cranks were factory errors, and put out for sale anyway. I mean when an engine builder has to sell motors as "30+" because the cranks in them might be like a box of chocolates, REALLY?

You're dead right about measuring cranks like those Dan; they better be in an engine with an indicator.