Classic NT fitting problem, caliber not aligned with the disk

Hi, installing a Grimeca NT front disk brake on a 20mm PX125 fork.  Back plate is properly installed (I double checked). Then I installed the hub. It spins freely. I opened the pads on the caliper the full amount. When I try and install the caliper the lower pad is scraping against the disk. Installed the caliper and the hub will not spin freely as its rubbing up against the pad.

What is causing this? How do I solve it? On the inside of the backplate, if I put a washer above the retaining clip, would that raise the hub a couple of mm's so the disk sits clear in the caliper?

 

Thanks

David

I took another look at it.  Normally a front hub nut it tightened to 45-60 ft-lbs. When I tighten the hub nut it just drives the hub down onto the caliper such that the disc rubs against the pad. I looked at a parts diagram and I am not missing any hardware.  What stops the hub from being driven too far down the axle?

What are you supposed to tighten the hub nut to? I could tighten it too just before it pushes the disk down on the caliper, and the cotter pin would stop it from backing off. But, will the hub move around because its not done down tight?

thanks

David