So, crankshaft pulley fell off my car because the key that the pulley shares with the lower timing belt pulley broke off.

Basically, I was wondering if and how can I replace that key without loosening the timing belt. The part that is still in there is in the timing belt pulley and I just really don't want to mess with the timing by messing with the belt tension.

 

You DO NOT have to mess with the timing.

 

With the pulley off, you should be able to see the snout of the crankshaft. If the woodruff key actually broke, whatever's left should be visible. If it came out, then you just need to get another. You should not have to go any further than the pulley to get to the woodruff indentation in the crank snout.