1996 4cyl. broken camshaft

I have a friend with a 96 passport. He had somebody replace the headgasket but they could not get the timing set right. Thats when i came into the picture. I found they had the cam gear on backwards I switched that and set the marks up according to the book. the engine was popping out the intake so i started checking and found that the cam was 180 off ? Put it back together and it ran fine for about a week and then the cam broke. I have a new one but i thought i would ask you all that have more knowlage than me if you had any ideas about this. Thanks for any help have.