Timing Chain vs. Timing Belt: What You Need to Know

The timing chain or a timing belt, is a component that plays a crucial role in engine performance and longevity, so understanding what’s under your bonnet is essential for proper maintenance.

• Timing Chain: A metal chain that connects the crankshaft to the camshaft inside the engine.
• Timing Belt: A reinforced rubber belt with hard teeth that interlock with the cogwheels of the crankshaft and the camshafts in a vehicle engine, and traditionally positioned outside the engine (dry belts).
• Wet Belt System: A newer evolution of the timing belt, wet belts operate inside the engine, running in oil to reduce friction and help meet emissions targets.

What does a timing chain or belt do?

Both the timing belt and chain synchronise the rotation of the camshaft and crankshaft, ensuring that engine valves open and close at the right time so the engine can work properly. If this system fails, it can cause poor performance, severe engine damage, or even complete failure.

How can it fail?

Over time, a timing belt or chain can wear down throwing the engine’s components out of sync, or in severe cases, snap. This can cause the valves to collide with the pistons, leading to significant internal damage. A broken belt or chain can also become entangled in other moving engine parts, compounding the damage and resulting in costly repairs. This is why regular maintenance and timely replacement are essential to keeping your engine running smoothly and preventing serious failures.

Wet belt systems are especially vulnerable to failure due to oil contamination. Impurities like soot and oxidised oil debris can accumulate between the belt teeth and pulleys, causing wear. As the outer coating of the belt deteriorates, the exposed inner materials are left in direct contact with oil, which may contain unburnt or partially combusted fuel that can further degrade the belt. Read more about damage to wet belt systems here. 

Which lasts longer?

Timing chains have long been considered the more durable option due to their metal construction and operation within the engine’s lubrication system. However, they are not immune to wear, particularly if oil changes are neglected, which can accelerate deterioration.

Timing belts have improved significantly over the years, with many modern versions lasting over 100,000 miles. In an effort to reduce weight and improve fuel efficiency, some manufacturers have introduced wet belt systems, and while these designs offer performance and emissions benefits, they are far more sensitive to poor maintenance. This makes regular oil changes with the correct specification even more critical to maintaining performance and preventing costly failures.

Which is better?

No option is strictly better, each has its pros and cons. Timing belts typically have scheduled replacement intervals, making it easier to plan for maintenance costs. Timing chains, on the other hand, often last longer but can be more expensive to replace if they wear out.

If you are buying a brand new car it should not be a concern, assuming you are planning to stick to the recommended service intervals, or even more frequent than that. If you’re buying an older car, knowing whether it has a belt or chain can help you anticipate potential maintenance needs.

Signs of a worn timing belt or chain

While visual inspections don’t always reveal wear, warning signs include:

• Oil leaks
• Poor performance
• Unusual engine noises
• Excessive smoke
• Overheating
• Rough idling
• Misfiring

Which vehicles are known to have issues with their timing chain or belt?

Jaguar Land Rover (JLR) has encountered significant challenges with timing chain failures, particularly in their 2 litre Ingenium diesel engines. These timing chains are prone to stretching over time, leading to misalignment, rough idling, and, in severe cases, complete engine failure. The root cause has been attributed to substandard materials used in the chains, resulting in excessive wear and premature failure. In response to these issues, certain regions have initiated recalls to address the problem. ​

Similarly, Ford’s 1 litre EcoBoost petrol engines and 2 litre EcoBlue diesel engines have experienced problems related to their wet timing belts, which operate within the engine oil. Over time, these belts can degrade due to oil contamination, leading to belt disintegration and potential clogging of the oil pickup. Such failures can cause significant engine damage, often necessitating complete engine replacement. Ford recommends replacing these belts at 150,000 miles or 10 years; however, numerous cases have been reported where the belts failed well before this interval, raising concerns about their longevity and reliability.

What can you do about it?

Use the correct oil

One of the most effective ways to protect your engine’s timing system, whether chain, belt, or wet belt, is to use a high-quality engine oil that not only meets the manufacturer’s specification but goes beyond it in performance and protection. Upgraded oils with advanced additive technology and low-friction formulations can significantly reduce wear on vital engine components, helping to prolong the life of timing systems that are prone to damage, particularly in poorly maintained or high-stress conditions.

Millers Oils new EE Performance C2 ECO 0w30 and EE Performance C5 ECO 5w20 have been developed specifically to tackle the known issues affecting timing chains in JLR vehicles and wet belt systems in Ford vehicles, including the 2 litre EcoBlue diesel engine commonly found in Transit vans. These vehicles are often used for heavy-duty applications and frequent stop-start driving, which puts additional strain on engine components.

Reduce oil drain intervals

The vehicle usage has an impact on the oil drain interval. If the usage is severe, a shorter oil drain period should be followed, such as: driving short journeys, stop-start driving, carrying and pulling heavy loads, or long periods of idling. In our experience, the oil drain interval should be halved.

Oil Sample Analysis

Rather than guessing when your oil needs changing, regular oil sample analysis is a proactive way to monitor engine health, especially in vehicles with known timing system vulnerabilities. By identifying signs of premature wear, fuel dilution, or contamination, you can detect early warning signs before they lead to serious failures. This is particularly valuable for engines with wet belt systems where debris or oil degradation can accelerate damage. Incorporating oil analysis into your maintenance routine allows you to make informed decisions on oil change intervals ultimately helping to prevent unplanned downtime and extend engine life.

More frequent chain or belt replacement

Vehicle manufacturers all have different recommended replacement intervals ranging from around 40,000 miles to over 100,000 miles. Some workshops and dealerships are now recommending shorter replacement intervals as belt failures are occurring at much lower mileages.

Read more about Reducing Damage to Wet Belt Systems here.

Find out more about EE Performance Engine Oil C2 ECO 0w30.

Find out more about EE Performance Engine Oil C5 ECO 5w20. 

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