Theres a hole that you put the locking peg ( or 6mm drill bit ) to lock the bottom pulley to the hole in engine block.
Check & double check the timing marks because these bottom pulleys do fail & if its in the early stages of failure you wont know until you go to change the timing belt.
You should really check all the timing marks line up before taking the old timing belt off.
What you may find is all the other timing marks will line up except the bottom pulley, you wont be able to get the locking peg anywhere near the hole in the engine block, if the bottom pulley has started to fail like this its time for a new one before it self destructs the engine.
Lee
June 2007