timing off for no reason.

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I just did the timing chain tensioner and the guide on the drive side which apparently the previous owner didnt feel was necessary to be in the engine. I did not take the chain off or any of the gears. Everything went together smoothly but now when i hook up the distributer, the rotor does not point to the driver side shock tower at 0 degrees as it should and as it was when i took it apart. Why is it now off if i didnt move anything? Could it be something with the oil pump? Thanks alot.