The timing chain is the engine component in your older GM engine that controls the engine timing. The chain is driven by the crankshaft and drives a single camshaft. The camshaft controls the opening and closing of the engine valves, as well as the rotation of the ignition distributor. As this chain ages, it can stretch, causing the engine timing to be off.
One of the easiest ways to check for a timing chain issue is with a timing light. Hook the timing light up to power and the number one spark plug. With the engine running, aim the light for the timing mark. If the chain has slipped, you will see the timing mark move around, instead of staying steady. If this happens, you will need to change the timing chain.
Replacement Parts You Will Need
New timing chain set: Double-roller is best
Water pump gasket
Timing chain gasket set
One gallon of premixed engine coolant
Tools and Equipment You Will Need
Coolant drain pan
SAE wrench set
SAE socket set with ratchet and five inch extension
Step 1: Drain the cooling system
Prior to removing any parts, the cooling system must be drained. Place the drain pan under the drain valve (Called a petcock valve) located at the lower driver side of the radiator. Open the petcock valve and loosen the radiator cap.
Step 2: Start loosening bolts
Loosen the bolts holding the fan to the water pump snout, fan shroud, and fan belts as the coolant drains. Remove the bolts securing the radiator brackets and remove the radiator brackets. Loosen the clamps on the upper and lower radiator hoses and heater hoses on the water pump.
Step 3: Remove the radiator hoses
Remove the upper radiator hose and heater hoses, making note of where they all go. Close the petcock valve and place the drain pan under the lower radiator hose. Remove the hose from the water pump and radiator. Gently lift the radiator out of the engine bay and set it aside. Cover the openings. Remove the fan shroud and felt belts.
Step 4: Remove the drive accessories
Remove the negative battery cable from the battery. Remove the power steering pump, A/C compressor (if so equipped) smog pump (if so equipped) and alternator and set them aside carefully. You will need the SAE wrenches and sockets for this step. The accessory bolts are most likely 9/16” or 5/8.” Identify the belts as to proper accessory and direction of rotation.
Step 5: Remove the lower pulley and timing set cover
The lower crank pulley needs to be removed to gain access to the timing set. Remove the center bolt (15/16” or 7/8”) most of the way, leaving it threaded into the crank approximately ¼”. Remove the pulley using the gear puller. The timing cover bolts are most likely 1’2” and there are ten of them. Starting at one corner and working around, remove the timing cover.
Step 6: Remove and replace front seal
This step can technically be skipped if the front seal isn’t leaking prior to starting the work, but it is recommended. There are special tools designed to remove and replace this seal, but you can pry it out with a flat screwdriver and install the new one by tapping it into place using a hammer.
Step 7: Rotate the engine to align timing marks
After removing the timing cover, reinstall the bolt in the crankshaft and rotate the engine so that the marks (arrows or dots) on the crankshaft and camshaft gears line up as close as possible. You should be able to draw a straight vertical line through the marks and the centers of both gears.
Step 8: Remove the gears and chain
Using a pick or screwdriver to lock the camshaft gear in place, remove the 5/8” bolt securing the gear to the camshaft. Once this bolt is removed, the two gears with the chain can be removed by sliding the crank gear off the nose of the crank. Some camshaft gears may be secured to the camshaft with three bolts, in which case the bolts are 7/16” or 1/2:” hex.
Step 9: Install the new gears and chain
Locating the woodruff keys (slots) on the inside of the gears so they line up with the keys (tabs) on the front of the camshaft and crankshaft, slide the lower gear over the snout of the crankshaft until it bottoms out. Slide the thrust washer/oil slinger over the crankshaft snout, lining up the keys. Torque the camshaft bolts to approximately 50 foot-pounds. Reinstall the crankshaft bolt and rotate the engine through two full revolutions and check the alignment of the timing marks.
Step 10: Replace the timing cover
Use an Emory cloth or gasket scraper to clean the timing cover and engine block mounting surfaces thoroughly. Apply a bead of RTV black to both surfaces and affix the replacement timing cover gasket to the timing cover. Thread the timing cover bolts into place and torque them to approximately 20-30 foot-pounds.
Step 11: Replace the water pump
Clean the water pump and engine block mounting surfaces thoroughly. Apply a thin coating of RTV blue to both the water pump and engine block. Using two bolts to keep the gasket from moving, affix the water pump gaskets) to the water pump and affix the pump to the front of the engine. Torque the bolts to between 20 and 30 foot-pounds.
Step 12: Attach the accessories and install drive belts
Slide the crank pulley over the snout of the crankshaft and install the bolt. Reattach the drive accessories (AC compressor, alternator, power steering pump, water pump/fan pulley, etc.) in the reverse order they were removed. Leave the pivot and slider bolts loose. Replace the drive belts on their appropriate accessories and tension the belts.
Step 13: Replace the radiator and fan shroud
Slide the fan shroud over the fan with the round opening toward the engine. Carefully slide the radiator into place and secure the radiator brackets. Attach the fan shroud to the radiator. Reattach the upper and lower radiator hoses as well as the heater and bypass hoses on the water pump.
Step 14: Refill the cooling system
If the coolant was in good condition and you were able to keep it free of contaminants, you can reuse it. However, even a little contamination is bad, so it’s recommend to replace the coolant. With the engine off, fill the radiator up to the neck of the radiator opening. Start the engine and allow it to warm up to operating temperature. Check and set the ignition timing at this time. Keep the engine running and keep adding coolant to just under the filler neck until the level no longer drops. Replace the radiator cap and check for leaks under the vehicle.
Note: On some older GM small block V8 engines, prior to removing the timing cover you will have to remove the mechanical fuel pump from the side of the engine/timing cover. There is also a fuel pump eccentric on the front of the camshaft that will have to be removed and replaced on these engines.