94 Eclipse 2.0L N/T ... timing belt jump?

[hellah fresh]

So about 2-3 weeks ago i installed a timing belt on for a friend and he was trying to be as cheap as he could so i just replaced the Timing belt with the pulley kit. So after it was al finished he drove it for about 2 weeks or so and all the sudding he hears a knocking noise and he brought it back to find out the piston hit the valve. So i was wondering what could cause the timing belt to jump like that? Also i forgot to mention that we did a valve job as well and now we are going to lose money for that. But what can cause a belt to jump?

[david-b]

Did you replace the tensioner when you did the timing job? I would never do a timing job without replacing the tensioner, even on a new one.

2 weeks is kind of far down the line to have problems from the timing job though. Usually you'd mess something up sooner. Does the timing belt have all its teeth on it?