Dspohr

I just bought a 1990 3.0L automatic 4 runner not running, I was told it needed a timing belt. When I got it home I took the timing covers off and when the marks on the cams were lined up the crank was out about 8 teeth so I lined them up and it started up, the next day I drove it to work and it ran fine, went out after work and when I went to start it it made a wired clicking noise so I tried cranking it again and the belt had jumped, thinking the belt might of been stretched I replaced the belt,water pump, tensioner, and idler got it back together set the timing and it ran great for a few days then the next day went to start it and it made the same clicking sound then the belt jumped again. I took the top cover off the belt is still tight but it's out on the crank again. Any ideas on what could cause the belt to keep jumping??