The timing chain on a Chevy 454, or a 7.4-liter engine only needs to be replaced when you hear it rattling. There is no specific time to replace it, as there is with timing belts. When reinstalling the timing cover, care must be taken to ensure that it is properly sealed, as oil is fed into the timing chain area to keep the chain lubricated, and it could leak out of the bottom of the timing cover. Chevy 454s are notorious for leaking at the bottom of the timing cover.
Ensure that the timing marks are still aligned. The mark on the camshaft sprocket should line up with the mark on the crankshaft sprocket. Insert the camshaft sprocket into the timing chain, making sure the mark on the sprocket is facing downward.
Fit the chain on the bottom of the crankshaft sprocket, and at the same time install the camshaft sprocket on the camshaft. Ensure that both sprockets are properly seated and that the timing marks line up, facing each other (the camshaft timing mark is at the 6 o'clock position, and the crankshaft timing mark is at the 12 o'clock position).
Install the camshaft sprocket retaining bolts and tighten them to 18 foot-pounds of torque. Clean the gasket mating surfaces on the timing chain cover and the block, if not already done. Smear a thin layer of RTV silicone on the timing cover's mounting surface. Fit the gasket into place.
Apply a 1/8-inch bead of RTV along the oil pan where the timing cover meets the pan, and along the mounting surface on the block. Allow the RTV to skin over -- when you touch it, it should not stick to your finger. Using more RTV along the oil pan is better than less, as this is where the timing cover tends to leak. Fit the timing cover on the block. Install the bolts and tighten them firmly.
Reinstall the harmonic balancer, using the harmonic balancer puller kit. Reinstall the crankshaft pulley, using the appropriate sockets. Tighten the bolts firmly. Clean the gasket-mating surface of the water pump and the block, if not already done. Smear a thin layer of RTV along the water pump's gasket-mounting surface. Fit the gasket on the water pump. Install the water pump on the engine and tighten the bolts firmly.
Reinstall the brackets for the power steering and air pump, if they were removed. Reinstall the power steering pump and air pump, if they were removed (not all vehicles with 454 engines have these options).
Reinstall the fan and tighten the bolts firmly, using the appropriate socket. Reinstall the accessory drive belts, using the belt diagram, which is located on the fan shroud or the underside of the hood. Adjust the tension on the belts by pushing the belt's accessory away from the engine and tightening the bolts in the slider brackets.
Slide the radiator into its brackets and tighten the retaining bolts firmly. Reinstall the upper and lower radiator hoses, and tighten the clamps. Close the petcock on the radiator, then fill it with coolant. Reinstall the radiator cap. Reconnect the negative battery cable.
