I can get the timing belt lined up on my 98 626 but when I crank it over the belt slips on the cam sprocket. The belt tension spring is working but this looks like a weak pattern to me, could the tensioner be weak or the spring weak or am I doing something wrong?

 

I had pulley tensioners which won't move with that small spring. For some reason they tighten up over time. Have try placing in vise
oiling & rotating didn't help. Replace the belt tensioner & spring if you have stretched by turning it counterclock to release the belt

 

gtxtreme is right. The spring that provides the tension on the belt tensioner pulley is very easy to overstretch. Should always be disconnected when rotating bearing to allow belt removal and install. Pull spring back off and look to see if it is stretched. Have run across some that had been overstretched but still did not allow belt to slip. Sure your cam is not siezed?