does your spacer have different ends? One large and one small? this allows for only one way to install the spacer in the hub.
It is this way on my 750..
Find out which way the spacer sits in the hub, then, you'll have to install the bearing nearest the spacers 'small' end, first. seat the bearing all the way down.
Now, insert the spacer, small end first into the hub, then tap in the other bearing to the point where it lightly touches the spacer.
the spacer should be snug, but movable.
lightly grease the inside of the spacer to ward off rust.