Drive Belt Tensioner Pulley

[lexus400]

I'm replacing the drive belt tensioner pulley. Got the old one off and it's shot, lots of noise from the bearing.

Anyway, put the new one on but it doesn't really sit flush/get tight enough against the tensioner. I need it go go in another 1/8" or so.

Is that normal ? Compared it to the old one and it's definitley the same part. Just seated the old one in place and it feels the same way ? It doesn't look keyed ? Any ideas ?

thanks