Vintage Dirt Bike Q & A

I have a problem I really hope someone can help me with....I am currently building/restoring a 76 CR250. I discovered that i had a bad crank bearing. Not wanting to split the cases, I bought a good lower end on Ebay. Everything looked fine...I installed the piston, cylinder, head etc. and put it in my bike. I removed the old rotor from my old lower end and attempted to install it on my new lower end that's when i discovered that the outside diameter taper on the crank of the new lower end was larger than the inside diameter of my rotor. see pics Does anyone know if there was a different crank offered for the CR in 76? Or what crank from another year has the larger spindle? If so, what rotor will fit on this? I thought about boring out the rotor to fit but I will give this forum a try first. I know the description is a little vague, but I hope someone has a solution!! Help!

You sure its not an my crank they had a bigger tapper as far as I know.

What kind of crank?

76 mr250 sorry