REPLACING TIMING BELT

You will need to get a manual on how to do this. Setting the timing is a very precise procedure requiring removal of the timing belt, re-timing the cam and crank gears to each other, etc. Suggest taking this to a mechanic as if done improperly major engine damage will result.

I agree with Littlehorn.

Old question, but for anyone stumbling on this -- Thanks to the timing marks on both cam gears and the crank gear, it's pretty easy to get everything resynchronized. If you don't have it already, download a copy of the Pathfinder factory service manual (google it, it's readily available). Align the marks on the cam gears to the marks on the case (roughly 12 o'clock position). Remove the distributor cap, make note of where spark plug wire #1 is, and use a wrench to rotate the crank till it's coming up on #1, then use the crank timing marks to bring it to exactly 0º TDC. The gears are now properly aligned in relation to each other. Swing the tensioner out of the way, and slip on the timing belt, making note of the directional arrow and alignment marks. The alignment marks will align with the marks on the cam gears. Set the tensioner, and reassemble all the pieces.