Timing chains and belts can wear out or break, requiring replacement. On the Chevrolet 350 engine, replacing the timing chain requires some disassembly. The timing chain and gears are located at the front of the engine, behind a timing cover, which is located behind the water pump. In the 1998 Chevy 1500 pickup, there is plenty of room to perform this repair. Still, several parts and some accessories need to be removed to gain access to the timing cover and chain/sprockets. A couple specialty tools also are needed to complete the job.
Place a coolant drain pan under the coolant drain valve (petcock) of the radiator and drain the coolant. Open the radiator cap to help the coolant flow more freely.
Remove the radiator fan shroud, then loosen and remove the accessory drive belt. Remove the radiator fan.
Loosen and remove any accessory brackets from the water pump, then remove the water pump.
Remove the lower belt-drive pulley from the harmonic balancer. Attach the balancer puller to the harmonic balancer and draw the balancer off of the crankshaft snout.
Loosen and remove all oil pan bolts except for the two rear-most ones. The objective is to lower the front of the oil pan enough to allow the timing cover to be removed without damage. It might be necessary to gently pry the oil pan from the block.
Remove the timing cover from the front of the engine block. You now have access to the timing chain and gears.
Rotate the engine, by hand, so that the timing marks are directly opposite each other. The cam sprocket mark will be in the six-o'clock position, and the crank sprocket mark will be in the twelve-o'clock position. Remove the three bolts on the cam sprocket and remove the sprocket and timing chain.
Use a sprocket puller if you are replacing the crankshaft sprocket. If the crankshaft sprocket is not worn at all, this step can be omitted. Likewise, the camshaft timing sprocket might not be worn and can be reused.
Install the replacement timing chain, making certain the timing markers are properly aligned. Tighten the cam sprocket bolts to 20 foot-pounds of torque.
Replace the front seal, located on the lower-front of the timing cover. Clean all gasket surfaces, then apply a modest amount of gasket sealer to the timing cover and reattach it to the engine block. Do the same for the oil pan gasket, which is located at the bottom side of the timing cover.
Re-secure the oil pan to the engine block and reassemble the engine/accessories in the reverse order of disassembly. Refill the engine coolant. Run the engine and check for leaks. Remedy as needed.
