With a roller cam you have to use a cam button on the front of the cam gear to stop it from walking forward into the cover. The cam button has to be adjusted so that there is the right amount of play. Also check your lifters you may have damaged them when the cam walked forward. This may have allowed the lifters to hit the lobe from the next one back. NOT GOOD. Regular cams are ground at a slight angle and the lifters are cut with a slight crown and they hit off center so that they rotate. This angle cut is toward the back so that is what keeps the cam back in the block. A roller cam is ground paralell to the axis and so are the lifters - so their isn't anything to hold the cam back in the block.