Just did a headgasket job on a 94 civic w/ a d15b7. I fire it up before putting on the crank pulley, accessories, timing cover and motor mount and literally as soon as I start it up the belt slides over and almost comes off. It came about 1/4 of an inch from coming off completely after running for 5 seconds. The belt was put on tight and was still tight when I shut the motor off. Does the crank pulley and/or timing cover have to be on to prevent this? Or what should I adjust or tweak to prevent this from happening?