Disconnect the battery cable, remove the valve cover, and set the engine at TDC on compression stroke. Mark timing chain links at camshaft sprockets, loosen sprocket bolts and remove the timing chain tensioner and camshaft sensor. Remove the sprocket bolts, disengage the timing chain, and hang it. Loosen camshaft bearing caps in reverse order and remove camshaft(s). Inspect lifters, camshafts, and bearings for wear. Check camshaft endplay, measure bearing journal, and camshaft lobe diameters. Engage sprocket teeth with the timing chain, and install sprocket bolts and timing chain tensioner. Complete installation in reverse order.