For camshaft and intermediate shaft installation in the 3.4L engine, lubricate the camshaft bearing journals and cam lobes with moly-base grease or engine assembly lube before installation. Slide the camshaft into the engine using a long bolt as a handle, supporting it near the block to avoid damaging the bearings. Install the camshaft retainer plate or intermediate shaft plate and tighten the bolts to the specified torque. For 2.5L engines through 1990, align the timing marks on the camshaft gear and crankshaft gear, then install and tighten the thrust plate bolts. For 2.2L four-cylinder and V6 engines (excluding 3800), dip the oil pump drive gear in engine oil and insert it into the block, ensuring it is flush with the mounting boss before securing it with a retaining bolt, and position a new O-ring on the oil pump drive shaft. Proceed with the installation of the lifters, timing chain, and sprockets based on the engine type. For the 3800 engine, lubricate the front bearing and rear journal of the balance shaft with engine oil, carefully insert it into the block, and use a hammer and socket to drive the front bearing into its insert just enough to install the balance shaft bearing retainer, then tighten the retainer bolts. Install the balance shaft driven gear and its bolt, turn the camshaft so the timing mark is straight down with the camshaft sprocket temporarily installed, and then turn the balance shaft so its timing mark points straight down. Install the camshaft gear that drives the balance shaft, aligning it with the keyway and matching the marks on both balance shaft gears by turning the balance shaft. Finally, after installing the camshaft sprocket, crankshaft sprocket, and timing chain, tighten the balance shaft driven gear bolt to the specified torque.