DB Engine :: Dropping A Primary Key Constraint - 35 Minutes And Counting

I have a copy of this database table and the first thing I noticed was that the Primary Key was pretty much useless and there were no sensible indexes.  Every query hitting this table ended up table scanning.So I thought I would try dropping the existing Primary Key constraint and then creating a more natural key that would make data retrieval quicker (hopefully).  I understand that creating a clustered index on this table is going to take a long time as ALL the data will need to be reorganised (I estimate this will take at least 1 hour).  However, just dropping the existing Primary Key constraint is taking forever.I can see that the server is doing a lot of disk reading/ writing and the wait type in Activity Monitor is PAGEIOLATCH_EX.I would have thought that just dropping a primary key would not change the data in the table, just delete the associated index.