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  • A bad timing gear will create a rattling noise from your engine. Your engine will also run rough or backfire. Sometimes, it might prevent the engine from running.
  • Timing gears are a gear train with two-to-one reduction that control valve timing in an internal combustion engine.
  • It’s not recommended to continue driving your vehicle if one or more of its timing gears has failed. A bad timing gear undermines the engine’s performance, which will make it harder to control your vehicle on the road.

Your vehicle depends on the timing gears to set the timing for the ignition process and many valves in the engine. If one or more of the gears wears out and fails, it will drastically affect how the engine runs. Fortunately, a bad timing gear will exhibit symptoms that warn you about its failure. Read on to learn more about this relatively small but critical engine part.

Bad Timing Gear Symptoms

A timing gear will exhibit certain warning signs when it has worn out or gotten damaged. If you encounter any of these symptoms, check the timing gears to determine if one or more of them needs replacement.

Here are the symptoms of a bad or failing timing gear: 

Rattling Sounds

Do you hear something rattle from the direction of your engine? One of the most common symptoms of a bad or failing timing gear is a rattling noise.

If a timing gear fails, it might rattle. Even if the gear itself doesn’t shake, it’s connected to the timing chain. A bad gear can lead to the chain grinding or rubbing against another part, which will damage both parts.

The symptom isn’t restricted to bad timing gears. Other engine parts can also cause rattling noises when they fail. Aside from the timing belt and timing chain, parts like the valve train, water pump, and harmonic balancer can rattle. Always run a thorough check of the engine to determine which part went bad.

Rough Running and Backfiring

A timing gear on its last legs might cause your vehicle’s engine to run rough. It might also lead to backfiring and cause a no-start condition.

The timing gears ensure that the engine’s valves open and close at the right time. Some of these valves control the volume of air and fuel that enters the cylinder. Others regulate the flow of exhaust fumes out of the engine and into the exhaust system.

If one of the timing gears stops working because of accumulated wear or damage, it might interfere with the valves. The engine might not get the correct volume of air and fuel it needs, or it might not expel the exhaust fumes at the best time.

Bad timing gears can also disrupt ignition timing. The spark plugs might fire at the incorrect time or in the wrong sequence. If the ignition timing is off, the engine might run rough while idling. An engine that runs rough will make strange noises, vibrate, and perform poorly.

The engine might also backfire because of bad gear timing. It’s an issue where the air-fuel mixture burns outside the cylinder. Backfiring damages the engine, so you should take action and replace the faulty part immediately.

Engine Doesn’t Run

In the worst-case scenario, a bad timing gear can stop the engine from running, which will render your vehicle immobile.

Normally, the timing gears enable the camshaft and crankshaft to move the timing chain. The chain synchronizes the intake and exhaust valves to open and close with the pistons moving inside the cylinders.

If one or more timing gears fail, the bad gears might prevent the camshaft and crankshaft from turning the timing chain. In addition to disrupting the synchronization of the intake and exhaust valves, it might also stop the two shafts from rotating.

An immobilized camshaft cannot move the intake and exhaust valves. Meanwhile, a crankshaft that cannot rotate cannot move the piston in the cylinder.

Bad timing gears, camshaft, crankshaft, and timing chain will stop the engine from operating. Given the connection between the timing gears and the ignition system, the engine might not start. You can end up stranded on the road, waiting for a tow.

What Is a Timing Gear?

The timing gears are a gear train with two-to-one reduction that control valve timing in an internal combustion engine.

These gears are keyed to the camshaft, which is why they’re sometimes also called camshaft timing gears. You can only fit them in a certain position. Furthermore, the gears are indexed together by marks on the gear teeth. If you replace a timing gear, you must align its timing marks per the manufacturer’s specifications.

If you intend to replace damaged or worn-out timing gears, consult the service manual or Haines manual of your vehicle for the step-by-step process. Some replacement products don’t come pre-set in the ready position, so you must spray air in certain ports to set the gears.

Look up the procedure for replacing timing gears because some of them come not set in the proper position, and you have to spray air in certain ports to set them in the ready position.

Anthony Harlin, ASE Certified Master Automobile Technician

To reduce noise and wear, timing gears have teeth made from soft materials like nylon. Nylon can grow brittle when exposed to high temperatures, which might lead to the fiber fracturing and flaking off the gear.

The rest of the gear is usually aluminum, iron, or steel.

What Does the Camshaft Timing Gear Do?

Thanks to the timing gears, the camshaft and crankshaft can drive the timing chain that sets engine timing. These parts work together to set the timing for the engine’s valves.

When the piston drops, the intake valves flip open to admit air and fuel into the cylinder. Once the piston rises, it’s the turn of the exhaust valves to open, allowing exhaust gases to leave for the exhaust system.

If the timing gears go bad, the intake valves won’t open and close properly. Air and fuel cannot enter the cylinder to mix together, and neither can the right air-fuel mixture stay inside.

Furthermore, the exhaust valves will stay instead of leaving. The hot gases can damage the cylinder, disrupt the air-fuel mixture, or deposit residue inside the cylinder.

Can You Drive Safely With a Bad Timing Gear?

It’s not recommended to continue driving your vehicle if one or more of its timing gears has failed. A bad timing gear undermines the engine’s performance, which will make it harder to control your vehicle on the road.

Furthermore, bad timing gears cause serious engine issues like rough running and backfiring. If you ignore these problems, you might end up with more costly engine repair jobs. In the worst-case scenario, you might need to replace the entire engine.

How Much Does a Replacement Timing Gear Cost?

A new timing gear can set you back anywhere between $30 and $350. The exact price can vary between products because of factors like the brand and your vehicle’s details. Individual gears are available, and you can also find them in some timing chain kits.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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