What a camshaft does and why it fails
A camshaft is a shaft inside your engine that controls when your intake and exhaust valves open and close. It has egg-shaped lobes (called cams) that push on valve lifters or rocker arms as the shaft rotates, timing the flow of fuel and exhaust gases in and out of each cylinder. When the camshaft wears out, you'll notice rough idle, loss of power, a ticking noise from the top of the engine, or a check engine light with a code pointing to camshaft timing.
Camshafts fail because of normal wear—the lobes gradually flatten over 100,000 to 200,000 miles—or because of oil starvation. If you've neglected oil changes, sludge builds up and starves the camshaft of lubrication, accelerating wear. A bent or broken camshaft usually results from a timing chain or belt failure that lets the valves and pistons collide.
Replacing a camshaft is a moderately advanced job. You'll need to remove the cylinder head (or at least the valve cover), rotate the engine to the right position, and carefully reinstall the camshaft with new gaskets. The difficulty depends on your engine layout: overhead cam engines (where the camshaft sits on top of the head) are easier than pushrod engines (where you work from below). If you're not comfortable with engine work, this is a good job to hand to a mechanic.
Key Takeaways
- You must remove the valve cover and often the cylinder head to access the camshaft, which requires draining coolant and disconnecting hoses.
- The engine must be positioned so the crankshaft and camshaft are at top dead center before you remove the old camshaft, or you risk valve damage.
- New camshaft bearings, gaskets, and seals should be installed during replacement, not reused from the old assembly.
- Camshaft replacement typically takes 4 to 8 hours depending on engine design, and you'll need a torque wrench to set bolt tension correctly.
- If the timing chain or belt is worn, replace it at the same time to avoid a repeat failure that damages the new camshaft.
Gather your tools and parts before starting
Before you begin, collect the right tools. You'll need a socket set, wrenches, a torque wrench (essential—camshaft bolts must be tightened in the correct sequence and to the correct tension), screwdrivers, pliers, and a gasket scraper. A compression tester is useful to confirm which cylinder has low compression if you suspect valve damage. You'll also want a drain pan for coolant and oil, jack stands if you're lifting the vehicle, and a clean workspace.
For parts, order a new camshaft, new camshaft bearings (if your engine uses replaceable ones), a new valve cover gasket, new intake and exhaust manifold gaskets if you're removing those, and a new timing chain or belt if it shows wear. Get the exact part numbers from your vehicle's service manual or parts catalog—camshafts are ground to specific profiles for your engine, and using the wrong one will cause poor performance or damage.
read or print your vehicle's service manual before you start. It contains the exact bolt torque specs, the sequence in which to tighten bolts, the position the crankshaft must be in, and any special tools your engine requires. Without it, you risk reassembling the engine incorrectly.
Position the engine and remove the valve cover
Park on level ground, set the parking brake, and disconnect the negative battery terminal. Drain the coolant by opening the drain plug at the bottom of the radiator into a pan. Drain the engine oil as well. Remove the air intake hose and any hoses or wires connected to the valve cover.
Locate the crankshaft pulley (the large wheel at the front of the engine) and the timing marks on it and the engine block. Rotate the engine by hand using a socket on the crankshaft bolt until the crankshaft timing mark aligns with the mark on the block—this is called top dead center (TDC). At this position, the camshaft timing mark should also align with its mark on the head or timing cover. Check your manual for the exact marks on your engine. This alignment is critical: if you remove the camshaft when the engine is not at TDC, the valves may be open, and you risk bending them.
Once the engine is at TDC, unbolt the valve cover. Use a gasket scraper to remove the old gasket and clean the sealing surfaces on the head and cover until they are smooth and free of debris. Do not gouge the metal.
Remove the camshaft and inspect the bearings
With the valve cover off, you can now see the camshaft. On overhead cam engines, the camshaft sits directly on the cylinder head and is held in place by bearing caps bolted across the top. On pushrod engines, you'll see rocker arms and pushrods instead, and the camshaft is lower in the block.
For overhead cam engines: unbolt the bearing caps in the reverse order of the tightening sequence listed in your manual (usually from the outside toward the center). Lift the camshaft straight out. Inspect the bearing surfaces on the head and the journals (the round surfaces) on the camshaft itself. They should be smooth and shiny. If they are scored, pitted, or discolored, the bearings have failed and must be replaced. If your engine uses replaceable bearing inserts, remove the old ones and press in new ones using a bearing driver tool (a specialized tool you may need to rent or borrow).
For pushrod engines: remove the rocker arms and pushrods first (mark their positions so you can reinstall them in the same spots), then unbolt and remove the camshaft from the front of the block. The process is similar—inspect the bearings and replace them if damaged.
Install the new camshaft and reassemble
Before installing the new camshaft, coat the lobes and journals with a break-in lubricant (a special oil designed for new camshafts). This reduces wear during the first few minutes of engine running. Slide the new camshaft into place, aligning the timing mark on the camshaft with the mark on the head or block.
Reinstall the bearing caps in the correct order (your manual will show this). Tighten the bolts in stages: first to a light snug, then to the final torque spec in the sequence your manual specifies. Do not skip steps or tighten all the way in one pass—this can warp the head. Use your torque wrench and tighten in a cross pattern (like tightening a car wheel) to may support even pressure.
For pushrod engines, reinstall the pushrods and rocker arms in their original positions. Adjust the valve clearance (the gap between the rocker arm and the valve stem) according to your manual. This is critical: too tight and the valves won't close fully; too loose and they'll clatter.
Install a new valve cover gasket and bolt the cover back on. Reinstall all hoses, wires, and the air intake. Refill the coolant and oil to the correct levels.
Check the timing chain or belt and start the engine
Before you start the engine, inspect the timing chain or belt. If it shows cracks, fraying, or slack, replace it now. A worn timing chain or belt will fail again and damage your new camshaft. If the chain or belt looks good, you can proceed.
Reconnect the negative battery terminal. Turn the key to the "on" position (do not start) and listen for the fuel pump to run for a few seconds—this pressurizes the fuel system. Start the engine and listen for any unusual noises. The engine should idle smoothly. If it idles rough, stalls, or makes a loud ticking noise, turn it off when ready and check your work: verify that the timing marks are aligned, that all bolts are tight, and that the valve clearance is correct.
Let the engine run for a few minutes, then turn it off and check for leaks around the valve cover gasket and any hoses you removed. If everything looks good, take the vehicle for a short test drive at low speed. The engine should feel normal. If the check engine light comes on, the engine may have a timing or sensor issue—do not ignore it.
When to call a professional mechanic
Camshaft replacement is a job you can do at home if you have engine experience, the right tools, and a service manual. However, call a mechanic if you discover that the timing chain is broken (this usually means the cylinder head is damaged and may need machine work), if the bearing surfaces are severely scored (they may need to be bored and fitted with oversized bearings), or if you're not confident rotating the engine to TDC or reading a torque wrench. A mistake in reassembly can bend valves or crack the head, turning a $300 part into a $2,000 repair.
Some engines also require special tools to hold the camshaft in place while you tighten the bearing caps, or to adjust the valve clearance. If your manual calls for tools you don't have, renting them may cost more than paying a mechanic to do the job.
Frequently Asked Questions
How do I know if my camshaft is actually worn and not something else?
A compression test will tell you. Remove all the spark plugs, screw the compression tester into one cylinder, crank the engine, and note the reading. Repeat for all cylinders. If one or two cylinders read much lower than the others, the valves in those cylinders are not sealing—a sign of a worn camshaft lobe or bent valve. If all cylinders are low and equal, the problem is likely piston rings, not the camshaft.
Can I replace just one lobe on the camshaft instead of the whole shaft?
No. The camshaft is a single piece of hardened steel, and individual lobes cannot be replaced or welded. You must replace the entire camshaft. However, if only one cylinder is affected, the problem may be a bent valve or a stuck lifter, not the camshaft itself—have a mechanic inspect before you order parts.
What is break-in lubricant and why do I need it?
Break-in lubricant is a special oil with additives that protect the camshaft lobes and bearings during the first few minutes of engine running, when wear is greatest. Standard engine oil does not have these additives. Most new camshafts come with a packet of break-in lubricant, or you can buy it separately. Skipping this step can cause premature wear of the new camshaft.
Do I have to replace the timing chain at the same time?
Not always, but it's a good idea. If the timing chain is worn, it will fail again and damage the new camshaft. Since you already have the engine apart, the labor cost to replace the chain is much lower than doing it separately later. If the chain looks new or has low mileage, you can leave it.
How long does a new camshaft last?
A properly installed camshaft with regular oil changes should last the life of the engine—100,000 to 200,000 miles or more. If you neglect oil changes or the timing chain fails again, the new camshaft will wear prematurely.