For the 3.4L engine, before starting, get two 6 x 1.0 mm bolts 16 to 20 mm long called service bolts is required. First of all, you should unlock and then unbolt the valve covers and the 
Timing Belt. Recommended that the engine is situated at TDC with reference to the number 1 piston. EACH OF the four camshafts is removed by first immobilizing the exhaust camshaft subgear then withdrawing the exhaust cam and finally the intake camshaft with due regard to the direction of the cams' timing marks. Next, using a service bolt fix the exhaust camshaft sub-gear to the driven gear, and while removing the camshafts, the camshafts should always be in level position. While tightening: turn the quantities of cap bolts for the camshaft bearing cap to the amount of 1/4 and remove both bearing caps and the exhaust camshafts; gently lift it up and level it. Repeat the same process for the intake camshaft and the other left hand cylinder head. Place the bearing caps back in order and then take out the valve lifters and shims with the help of a magnetic tool and store them away. On removal of a camshaft gear, the cam must be fixed in the vise, apply a service bolt in the ungeared hole and rotate the sub-gear in the clockwise direction to come out the first service bolt. Take out the Sub-gear snap-ring and the wave washer sub-gear and the CAMSHAFT GEAR SPRING. For installation, to assemble the exhaust camshaft gear, screwing of the components are done in reverse manner and for holding the camshaft in position, padded vise is used and the location of the holes of the camshaft driven gear and sub-gear is also aligned before tightening of the service bolts. Coat the lifters with RG or assembly lube on the flat as well as the camshaft components, align the intake camshaft such that its timing marks face the exhaust side and put on the bearing caps in numerical sequence. Remove the bearing cap bolts and replace the camshaft oil seal also tighten the bolts. As for the exhaust camshaft, the procedure should be the same which means to align the camshaft and to tighten it. Return all the parts in reverse order and tighten the nuts, and use grease where required in the place of the sealant. Last, turn on the engine and look for drip and make sure every gear is in its correct function. In the aspects of 3.0L parts removal, the operation includes the removal of the valve covers, timing belt, number 3 timing belt cover and the camshaft housing rear cover on the right bank. Tighten the camshaft bearing cap bolts in the amount of 1/4 turn, take off the bearing caps and carefully lift the camshaft up, but ensure that it is slightly oriented horizontally. React for the left bank, and put the bearing caps in order. Place cookies of grease or assembly lube on the lifters or cams of the camshaft and put the camshafts in position where the bearing caps go in front. On the mating surfaces, coat with sealant. I recommend that you how to replace the bearing cap bolts and camshaft oil seal. Perform the final installation of the rest of the components in the reverse sequence to the removal and apply sealant where necessary, then start up the engine and check for any leakage or improper functioning.