What a timing chain does and why it fails
A timing chain synchronizes your engine's crankshaft and camshaft so that the intake and exhaust valves open and close at exactly the right moment. If the chain stretches, breaks, or jumps a tooth, the valves will open and close at the wrong time — your engine will run rough, lose power, or stop running altogether. A broken timing chain can also cause the pistons to collide with the valves, which damages the engine beyond repair.
Timing chains wear out over time because they are under constant tension and friction. Most chains last between 80,000 and 200,000 miles, depending on your engine, driving habits, and maintenance. Signs of a failing chain include a rattling noise from the front of the engine (especially on cold starts), a check engine light, rough idling, or difficulty starting. Some engines use a timing belt instead of a chain; a belt is quieter but wears out faster and must be replaced on a fixed schedule.
Key Takeaways
- Timing chain replacement requires removing the engine cover, crankshaft pulley, and timing cover — a job that takes 4 to 8 hours for most vehicles and demands careful attention to bolt torque specifications.
- You will need a socket set, a torque wrench, a timing light or dial indicator, and engine-specific tools such as a crankshaft pulley holder or camshaft locking tool; renting or borrowing these tools can save money.
- The hardest part is aligning the crankshaft and camshaft marks before you remove the old chain, because if you lose alignment, reassembly becomes much more difficult.
- Timing chain replacement is a good time to replace the tensioners, guides, and sprockets at the same time, because they wear together and you will already have the engine apart.
- If you have never done engine work before, this job is more difficult than brake pads or an oil change but less difficult than a full engine rebuild.
Tools and parts you will need before you start
Gather your tools before you begin, because stopping halfway through to hunt for a socket or wrench will cost you time and risk leaving fasteners loose. You will need a full socket set (metric and standard, depending on your vehicle), a torque wrench that reads in foot-pounds or Newton-meters, a breaker bar for stubborn bolts, and a set of screwdrivers. Most timing chain jobs also require a crankshaft pulley holder or strap wrench to keep the crankshaft from spinning while you remove the large bolt that holds the pulley in place.
Engine-specific tools vary by manufacturer. Some engines require a camshaft locking tool to hold the camshaft in place during removal and installation. Others need a timing light or dial indicator to verify that the crankshaft and camshaft are aligned before you reassemble. Check your vehicle's service manual or a repair database like AllData or Mitchell1 to see which tools your engine needs. Many auto parts stores rent these tools for a deposit that you get back when you return them.
For parts, you will need a new timing chain, new sprockets (crankshaft and camshaft), new tensioners, and new guides. Buy a complete timing chain kit rather than just the chain, because the tensioners and guides wear at the same rate as the chain and will fail soon if you do not replace them. You will also need a new gasket for the timing cover and new seals for the crankshaft and camshaft. A gasket set designed for your vehicle will include all of these.
Removing the engine cover and crankshaft pulley
Start by disconnecting the negative terminal of the battery to prevent accidental electrical shock. Remove the engine cover (usually held by clips or a few bolts) and set it aside. Drain the coolant into a clean container if your timing cover is close to the radiator or water pump — you may need to remove hoses to access the cover.
Next, remove the serpentine belt (also called the drive belt) by loosening the tensioner bolt and sliding the belt off the pulleys. Take a photo of the belt routing before you remove it, or draw a diagram on a piece of tape, so you know how to reinstall it. Some vehicles have a belt routing diagram under the hood or in the owner's manual.
Now remove the crankshaft pulley. This is the large wheel-shaped part bolted to the front of the crankshaft. Use your crankshaft pulley holder or strap wrench to keep the crankshaft from spinning, then use a socket and breaker bar to loosen and remove the center bolt. The bolt is usually very tight — do not be afraid to use leverage, but do not strip the bolt head. Once the bolt is out, use a pulley puller (a three-armed tool that bolts to the pulley and pulls it straight off) to remove the pulley itself. Do not try to pry it off with a screwdriver, because you will damage the crankshaft.
Locating and marking the timing marks
Before you remove anything else, you must locate and mark the timing marks on the crankshaft and camshaft. These marks tell you when the engine is at top dead center (TDC), the point where the number one piston is at the top of its stroke and both valves for that cylinder are closed. If you lose this alignment, the engine will not run correctly when you reassemble it.
The crankshaft timing mark is usually a notch or line on the crankshaft pulley or a mark on the crankshaft itself. The camshaft timing marks are usually dots or lines on the camshaft sprockets. Consult your service manual to find the exact location of these marks on your engine — they vary widely. Rotate the crankshaft by hand (using the pulley bolt or a breaker bar on the crankshaft) until the crankshaft mark aligns with a fixed reference point on the engine block, usually a pointer or a line on the timing cover.
Once the crankshaft is at TDC, check that the camshaft marks also align with their reference points. If they do not, rotate the crankshaft one full turn (360 degrees) and check again. When both marks are aligned, use a marker or paint pen to draw a line across the chain and both sprockets so you can see exactly where they were. This mark will help you reinstall the chain in the correct position.
Removing the timing cover and old chain
Remove all bolts holding 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 on a clean surface so you remember which bolt goes where. Carefully pry the cover away from the block using a plastic scraper or old credit card — do not use a metal tool, because you will gouge the gasket surface and create a leak.
Once the cover is off, you can see the timing chain, sprockets, tensioners, and guides. Before you touch anything, take several photos from different angles so you have a reference if you get confused during reassembly. Now loosen the bolts on the camshaft sprocket and crankshaft sprocket and slide them off the chain. Some engines require you to hold the camshaft with a locking tool while you loosen the sprocket bolts — check your manual.
Remove the old chain by sliding it off the sprockets. If the chain is very tight or stuck, you may need to loosen the tensioner or remove the guides to create slack. Once the chain is out, remove the old tensioners and guides by unbolting them from the engine block. Inspect the crankshaft and camshaft sprockets for wear — if the teeth are hooked or worn flat, replace them. If they look good, you can reuse them, but most shops replace them as part of the kit.
Installing the new chain, sprockets, and tensioners
Clean the timing cover gasket surface with a plastic scraper and solvent to remove all traces of the old gasket. Do the same for the engine block surface. Any old gasket material left behind will cause the new gasket to leak.
Install the new crankshaft sprocket by sliding it onto the crankshaft. It will only fit one way because of the keyway (a slot in the sprocket that matches a key on the crankshaft). Install the new camshaft sprocket the same way. Do not bolt them down yet — you need to thread the new chain onto both sprockets first.
Lay the new timing chain over both sprockets so that your alignment marks (the ones you drew on the old chain) line up with the marks on the new sprockets. If your new chain does not have marks, align the chain so that a bright link (usually a silver or painted link) on the chain lines up with the timing mark on each sprocket. Once the chain is threaded correctly, bolt the sprockets to the crankshaft and camshaft. Use your torque wrench to tighten the bolts to the specification in your service manual — over-tightening will strip the threads, and under-tightening will cause the sprocket to slip.
Install the new tensioners and guides in the positions where the old ones were. Tighten all bolts to specification. The tensioner is spring-loaded and will automatically take up slack in the chain as the engine runs, so do not try to manually tension the chain.
Reassembling the timing cover and engine
Install a new gasket on the timing cover by laying a thin bead of gasket maker around the cover surface, then pressing the gasket into place. Some gaskets are pre-glued and do not need additional sealant — check the instructions that come with your gasket kit. Carefully position the timing cover over the chain and sprockets and bolt it down. Start with the bolts by hand to make sure the cover is aligned, then tighten them in a crisscross pattern (like tightening wheel lugs) to may support even pressure. Use your torque wrench to tighten each bolt to specification.
Reinstall the crankshaft pulley by sliding it back onto the crankshaft and hand-tightening the center bolt. Use your pulley holder and torque wrench to tighten the bolt to specification — this bolt is critical and must be tight. Reinstall the serpentine belt by routing it around the pulleys according to your diagram or the routing label under the hood. Adjust the tensioner so the belt has the correct amount of slack (usually about half an inch of play in the middle of the longest span).
Refill the coolant if you drained it, reconnect the negative battery terminal, and start the engine. Listen for any rattling or grinding noises from the front of the engine. If the engine starts and runs smoothly without noise, you have done the job correctly. If you hear a rattling noise, stop the engine when ready and check that all bolts are tight and that the chain is properly tensioned.
Frequently Asked Questions
How do I know if my timing chain is actually broken or just stretched?
A stretched chain will rattle, especially on cold starts, but the engine will still run. A broken chain will stop the engine completely and prevent it from starting. If your engine cranks but will not start, or if it starts and when ready stalls, the chain may be broken or jumped several teeth. A timing light or stethoscope held against the front of the engine will help you hear whether the chain is rattling.
Can I replace just the chain without replacing the sprockets and tensioners?
You can, but it is not recommended. The sprockets and tensioners wear at the same rate as the chain, and replacing only the chain often means you will have to do the job again in a few thousand miles. Most shops include all three in a timing chain kit for this reason. The extra cost of the sprockets and tensioners is small compared to the labor cost of doing the job twice.
What happens if I lose the timing marks and do not know where the chain goes?
If you lose alignment, you will need to rotate the crankshaft until the number one piston is at top dead center again, then align the camshaft marks to match. A timing light or dial indicator will help you find TDC. If you cannot find the marks or you are unsure, stop and consult your service manual or a repair forum for your specific engine — reassembling with the chain one tooth off will cause serious engine damage.
Do I need to remove the engine from the vehicle to replace the timing chain?
Most vehicles allow you to replace the timing chain without removing the engine, but some do not. Check your service manual for your specific vehicle. Some engines require you to remove the engine, transmission, or both to access the timing cover. If your manual says the engine must come out, this job is beyond the scope of a home garage project.
How long does a new timing chain last?
A new timing chain should last as long as the original — typically 80,000 to 200,000 miles. The lifespan depends on your driving habits, maintenance schedule, and engine design. Keeping your oil clean and changing it on schedule will help your new chain last as long as possible, because dirty oil causes the chain to wear faster.