Grizzly T27417 oscillating sander problem

I cannot get the belt on my sander to lock into place. I have sent the sanding head back once. They tightened the bolts.lock worked for less then 5 minutes when returned. My question is about the cam on the tensioner. With no belt installed the cam stays in contact. With a belt there is about a 1/4 inch gab between the cam and the tensioner. Is this normal? It does not seem to be as the only thing holding the tensioner foward is the bolt.