What a Timing Chain Does and Why It Fails

A timing chain is a metal chain inside your engine that synchronizes the crankshaft and camshaft—two rotating shafts that must turn in exact time with each other. The crankshaft controls the pistons moving up and down; the camshaft controls the valves opening and closing. If they fall out of sync by even a tooth, your engine will not run, or it will run so badly that it damages itself.

Timing chains wear out over 80,000 to 200,000 miles, depending on your engine, your driving habits, and how well you keep up with oil changes. A worn chain stretches, which throws off the timing. You may hear a rattle from the front of the engine, especially when you start it cold. Eventually the chain can skip a tooth, snap, or fall off the sprockets entirely—and when that happens, the engine stops running and may suffer internal damage that costs thousands to repair.

Replacing a timing chain is a major job because the chain sits deep inside the engine, behind the timing cover. You have to remove the cover, drain coolant, unbolt the water pump, and sometimes remove the radiator. On some vehicles, you also remove the cylinder head. The job takes 4 to 8 hours for a mechanic and costs $500 to $2,000 in labor alone, depending on your vehicle. This guide walks you through the process so you understand what the work involves and can follow along if you are doing it yourself.

Key Takeaways

  • A timing chain synchronizes your crankshaft and camshaft; when it wears out or breaks, your engine will not run and may suffer internal damage.
  • You must drain the coolant, remove the timing cover, water pump, and sometimes the radiator before you can access the chain.
  • The crankshaft and camshaft must be positioned at exact marks before you remove the old chain and install the new one, or the timing will be wrong.
  • Most timing chain jobs also require replacing the timing chain tensioner and guides, which wear at the same rate as the chain itself.
  • After installation, you must refill the coolant, check that the engine starts and idles smoothly, and verify that the timing marks are still aligned.

Gather Your Tools and Parts Before You Start

Timing chain replacement requires both common tools and some specialized equipment. You will need a socket set, wrenches, screwdrivers, a torque wrench, and a drain pan for coolant. You will also need a timing light or a way to see the timing marks on the crankshaft and camshaft—usually a mark on the crankshaft pulley and marks on the camshaft sprockets or the cylinder head. Some vehicles have a small window in the timing cover for this purpose.

Before you begin, order the replacement parts for your specific vehicle: the timing chain itself, the timing chain tensioner, the timing chain guides (usually two or three pieces), a new timing cover gasket, and a new water pump gasket. Many shops replace the water pump at the same time because you have already removed it. Check your vehicle's service manual to see whether your engine also requires new camshaft or crankshaft seals. Buy a new coolant drain plug if yours is aluminum and has been removed before—aluminum plugs can strip easily.

Gather a service manual for your vehicle before you start. The manual will show you the exact location of the timing marks, the order in which to remove bolts, the torque specifications for reassembly, and any special tools your engine requires. Without this information, you risk installing the chain incorrectly and damaging the engine.

Position the Engine at Top Dead Center

Before you remove anything, you must position the crankshaft and camshaft at their correct starting positions. This is called top dead center (TDC), and it ensures that when you install the new chain, the timing will be correct. Turn the crankshaft by hand using a socket on the crankshaft pulley bolt until the crankshaft mark aligns with the mark on the engine block or timing cover. At the same time, the camshaft mark (usually on the camshaft sprocket or the cylinder head) must align with its corresponding mark.

Some engines have a small hole in the cylinder head or block where you can insert a pin or bolt to lock the camshaft in place once it is at TDC. Check your service manual to see whether your engine has this feature. If it does, insert the pin once the camshaft is aligned—this prevents the camshaft from rotating while you work on the chain. Do the same for the crankshaft if your engine has a crankshaft locking pin.

Take a photo of the timing marks before you begin disassembly. This gives you a reference if you lose track of the position while you are working.

Remove the Timing Cover and Access the Chain

Drain the coolant by opening the drain plug at the bottom of the radiator or engine block and letting it flow into a drain pan. Once the coolant has drained, remove the bolts that hold the water pump in place and pull the pump away from the engine. You may need to remove the radiator hose clamps first. Set the water pump aside—do not discard it yet, because you will need to transfer the pulley to the new pump if you are replacing it.

Next, remove the bolts that hold the timing cover to the engine block. The cover is usually held by 8 to 12 bolts of different lengths, so lay them out in order as you remove them so you can reinstall them in the correct holes. Once all bolts are out, carefully pry the cover away from the block using a plastic pry tool or a wooden block and hammer. Do not use a metal screwdriver, which can gouge the sealing surface and cause oil leaks. If the cover is stuck, tap gently around the edges to break the gasket seal.

Once the cover is off, you will see the timing chain, the crankshaft sprocket, the camshaft sprocket or sprockets, and the chain tensioner. Verify that the timing marks are still aligned as you positioned them. If they have moved, reposition the crankshaft and camshaft and lock them again before proceeding.

Remove the Old Chain, Sprockets, and Tensioner

Release the tension on the chain by unbolting the timing chain tensioner. The tensioner is a spring-loaded device that keeps the chain tight; once you remove it, the chain will go slack. Remove the tensioner completely and set it aside. You will not reuse it—timing chain tensioners wear out at the same rate as the chain and must be replaced.

Next, unbolt the camshaft sprocket or sprockets. Most engines have one sprocket per camshaft, but some have two. Mark each sprocket with a paint pen or tape so you know which one came from which camshaft if you have multiple cams. Once the sprockets are unbolted, slide them off the camshaft along with the timing chain. The crankshaft sprocket usually stays on the crankshaft—you will remove it only if it is damaged or if your service manual requires it.

Remove the timing chain guides. These are usually plastic or metal rails that the chain rides on. There are typically two or three guides, and they bolt to the engine block or cylinder head. Remove all bolts and take out the guides. Inspect them for cracks or excessive wear. Even if they look okay, replace them with new ones—guides wear as the chain wears, and a worn guide will cause the new chain to wear prematurely.

Install the New Chain, Sprockets, and Tensioner

Install the new timing chain guides first, using the bolts you removed earlier. Torque them to the specification in your service manual—usually 15 to 25 foot-pounds. Make sure the guides are seated flush against the engine block or head.

Slide the new timing chain onto the crankshaft sprocket. The chain has a master link (a link with a removable clip) that makes installation easier. Position the chain so that the timing marks on the crankshaft sprocket align with the mark on the engine block, just as they were before. Once the crankshaft sprocket is correctly positioned, slide the camshaft sprocket or sprockets onto the camshaft with the chain wrapped around them. Align the timing marks on the camshaft sprocket with the marks on the cylinder head or block.

Bolt the camshaft sprocket or sprockets back onto the camshaft, using the bolts you removed earlier. Torque them to the specification in your manual—usually 40 to 60 foot-pounds. Double-check that the timing marks are still aligned. If they have shifted, loosen the sprocket bolts slightly, reposition the sprocket, and retorque.

Install the new timing chain tensioner. The tensioner has a spring inside that will automatically take up slack in the chain once it is bolted in place. Bolt it down and torque it to specification. Once the tensioner is installed, rotate the crankshaft by hand two full turns to make sure the chain does not bind and the timing marks come back into alignment. If the marks do not align after two full rotations, the chain is installed incorrectly and must be removed and reinstalled.

Reinstall the Timing Cover and Refill Coolant

Clean the sealing surface of the timing cover and the engine block with a gasket scraper or plastic brush. Remove all old gasket material and oil. Wipe the surface clean with a lint-free cloth. Install a new gasket on the timing cover—some gaskets are glued to the cover, while others are loose and must be held in place as you bolt the cover on.

Position the timing cover on the engine block and insert the bolts. Start all bolts by hand first so the gasket seats evenly. Then torque each bolt to the specification in your manual, usually 15 to 25 foot-pounds. Torque in a crisscross pattern (like tightening a wheel) so the cover seats evenly and the gasket does not squeeze out unevenly.

Reinstall the water pump using a new gasket. Torque the water pump bolts to specification. Reconnect the radiator hose and tighten the clamp. Refill the coolant system with the correct type of coolant for your vehicle—check your owner's manual or the label under the hood. Fill the radiator, the overflow tank, and the coolant reservoir. Start the engine and let it run for a few minutes, then turn it off and check the coolant level again. Top off if needed.

Start the Engine and Verify the Timing

Turn the key and start the engine. It should start smoothly and idle without rough running or knocking. If the engine cranks but does not start, or if it starts and then stalls, the timing may be off. Turn off the engine when ready and recheck the timing marks. Do not run the engine if you suspect the timing is wrong, because running an engine with incorrect timing can cause internal damage.

Once the engine is running smoothly, let it warm up to operating temperature. Watch the temperature gauge to make sure it rises normally and does not overheat. Check for coolant leaks around the timing cover gasket and water pump gasket. If you see leaks, turn off the engine and let it cool, then tighten the bolts slightly. Do not over-tighten, which can crack the cover or strip the bolt holes.

Take the vehicle for a short test drive at low speed. The engine should run smoothly without knocking, pinging, or hesitation. If you hear a knock or ping, the timing may be slightly off. Return to the shop and recheck the timing marks. Once you are confident the timing is correct and the engine runs smoothly, the job is complete.

Frequently Asked Questions

Can I replace just the timing chain without replacing the tensioner and guides?

No. The tensioner and guides wear at the same rate as the chain. If you replace only the chain, the worn tensioner and guides will cause the new chain to wear prematurely and may fail within a few thousand miles. Always replace all three components together.

What happens if I install the timing chain one tooth off?

If the chain is off by one tooth, the camshaft will open and close the valves at the wrong time. The engine may not start, or it may start and run very roughly with severe knocking. Running the engine in this condition can bend the valves or damage the pistons. Always verify the timing marks before starting the engine.

How long does a new timing chain last?

A new timing chain typically lasts 80,000 to 200,000 miles, depending on the engine design, your driving habits, and how well you maintain the oil. Frequent oil changes and using the correct oil viscosity help the chain last longer.

Do I need to remove the cylinder head to replace the timing chain?

On some engines, yes. Check your service manual for your specific vehicle. Some engines allow you to access the chain without removing the head, while others require it. Removing the head adds several hours of labor and requires additional gaskets and seals.

What should I do with the old coolant after I drain it?

Take the old coolant to a recycling center or auto parts store that accepts it. Do not pour it down the drain or into the ground—coolant is toxic to humans and animals. Many auto parts stores will take it for free or a small fee.