Pulled water pump from motor to see a hair line crack in timing cover. Is this a major issue what could crack the housing case?

 

Would definitely get it replaced. That's not a part you want cracked by any means. I would also go ahead and change your timing chains.

 

I'm not doubting your ability to visually inspect a crack but are you sure it's not just some kind of splatter or some sealing glue?

If it is cracked one I apologize no disrespect intended and I would replace the cover you don't need the crack become larger and allow for debris to get in as this would obviously cause a potentially large problem of the timing chain jumps.

I'm not saying I would do it but if it is something you can't tackle yourself and looking for a temporary fix you could use a little JB weld to buy some time financially or just until you find the time to replace it yourself or have someone else tackle the job.

As far as replacing the chains I wouldn't unless you see a problem when you crack the cover. No need to open a can of worms if you can avoid it