I'm going to copy the procedure from Autozone.com below. I've never seen such a complicated way of getting the tension right, but better to follow their instructions, I guess. Note that they ask you to loosen the rocker shafts, but they never tell you to put them back. I will add that.
6. Remove both cylinder head covers and loosen all rocker arm shaft retaining bolts.
The rocker arm shaft bolts MUST be loosened so that the correct belt tension can be obtained.
A good way (although rather tedious) to check for proper timing belt installation is to count the number of belt teeth between the timing marks. There are 133 teeth on the belt; there should be 40 teeth between the timing marks on the left and right-side camshaft sprockets, and 43 teeth between the timing marks on the left-side camshaft sprocket and the crankshaft sprocket.
- Install the tensioner and the return spring. Using a hexagon wrench, turn the tensioner clockwise, then temporarily tighten the locknut.
- Make sure that the timing belt is clean and free from oil or water, before installation.
- Install the timing belt. Align the white lines on the belt with the punchmarks on the camshaft and crankshaft sprockets. Be sure to have the arrow on the timing belt pointing toward the front belt covers.
- While keeping the tensioner steady, loosen the locknut with a hexagon wrench.
- Turn the tension approximately 70-80 degrees clockwise with the wrench, then tighten the locknut.
- Turn the crankshaft in a clockwise direction several times, then slowly set the No. 1 piston to TDC of the compression stroke.
- Apply 22 lbs. (10 kg) of pressure (push it in) to the center span of the timing belt between the right-side camshaft sprocket and the tensioner pulley, then loosen the tensioner locknut.
- Using a 0.0138 in. (0.35mm) feeler gauge (the actual width of the blade must be 1/2 in. or 12.7mm thick), positioned as shown in the illustration, slowly turn the crankshaft clockwise. The timing belt should move approximately 2 1/2 teeth. Tighten the tensioner locknut, then turn the crankshaft slightly and remove the feeler gauge.
- Slowly rotate the crankshaft clockwise several more times , then set the No. 1 piston to TDC of the compression stroke; recheck all alignment marks.
- Install the upper and lower timing belt covers.
- Connect the negative battery cable.
When installing the rocker arm shafts, be certain that they are installed in their original positions.
- Make sure the camshaft knock pin is at the top of the camshaft and that the lobe is not in the lifted position. If servicing the left-side cylinder head, set the No. 1 piston at TDC of its compression stroke, then tighten the rocker shaft bolts for cylinder No. 2, 4 and 6 cylinders. If servicing the right-side cylinder head, set the No. 4 piston at TDC of its compression stroke and tighten the rocker shaft bolts for cylinder No. 1, 3 and 5 cylinder rocker shaft bolts. Tighten all bolts gradually, in two or three stages, to 13-16 ft. lbs. (18-22 Nm).
- Install the cylinder head cover(s).