It's difficult to tell from the photos, but the new sprocket looks like it may have slightly longer pitch than normal, but that doesn't explain why the new chain doesn't fit the old sprocket The chain seems a little odd, but visually it's hard to say why. A 428 chain should have 1/2 " pitch, .335 diameter rollers and .205 inside width. You might also try laying one sprocket on top of the other to see if the teeth match up.