Before removing the camshafts, check the valve clearances. Remove the primary timing chain and camshaft VCT units, then take out the camshafts from the cylinder head. With the camshafts removed, the tappets can be extracted using a magnet. After removing the camshafts, clean them with solvent and inspect the bearing journals for uneven wear and pitting; if damaged, the bearing saddles in the cylinder heads and caps will likely need replacement. Measure the bearing journals with a micrometer and compare to the specifications to check for excessive wear or out-of-round conditions. Measure the camshaft lobe height and the base circle to determine lobe lift, recording this figure for future reference and repeating the check on the remaining camshaft lobes while comparing results to the values. Inspect the camshaft lobes for heat discoloration, score marks, chipped areas, pitting, and uneven wear; if they are in good condition and the lobe lift measurements are as specified, the camshafts can be reused. For installation, rotate the crankshaft counterclockwise to position the keyway in the 9 o'clock position, lubricate the tappets with clean engine oil, and reinstall them in their original locations, replacing any out-of-specification tappets with new ones of the proper thickness. Obtain new seals for the grooves at the front of each camshaft and install them with the split facing up. Lubricate the camshaft bearing journals and cam lobes with moly-based grease or camshaft installation lubricant, then position the camshafts in the cylinder head in their neutral positions. Install the camshaft bearing caps in their original locations and tighten the bolts in sequence to the specified torque. Recheck the valve clearances, ensuring the crankshaft is in the neutral position to allow the camshafts to turn without the valves contacting the pistons. Remove the camshaft cap bolts securing the valvetrain oil tubes and take out the oil tubes. Rotate the camshafts to position the dowel pins correctly for installing the VCT units and secondary timing chains, then install the camshaft holding tools. Install the VCT units, rotate the crankshaft clockwise to position the keyway in the 11 o'clock position, and install the primary timing chain. Reinstall the valvetrain oil tubes and tighten the bearing cap bolts to the specified torque. The remaining installation steps are the reverse of removal, and before starting the engine, refill the cooling system, change the oil, and install a new oil filter.