Timing Belts vs Timing Chains: What’s the Difference?

Popularised by overhead camshafts appearing on road car engines from the 1970s, the once durable, last-for-life timing chain was replaced on many models by an externally-mounted replaceable timing/cam belt. Later, timing chains made a comeback and are fitted to many cars today.

Timing belts and timing chains perform the same main purpose: to synchronise the engine crankshaft and camshaft. This is necessary to ensure that the valves and pistons do not make sudden, unexpected, violent and expensive contact.

If you are a non-technical reader and have made it this far into this blog, the result of a timing chain, or belt, breaking tends to be a ruined engine and a hideously large repair bill.

Furthermore, modern timing belts and chains on modern engines tend to drive other components too, including various pumps and balance shafts.

What is a Timing Belt?

As pictured, timing gears, situated outside the main engine, rely on a tensioned fibrous belt that possesses teeth that bear against the camshaft and crankshaft pulleys.

However, some engines, notably those produced by Ford Motor Company and the Stellantis group (used especially Citroen, Peugeot, Vauxhall/Opel, plus some Toyotas and Hondas) possess 'wet belts', or 'Belt In Oil'. These belts are situated inside the engine and are lubricated by engine oil. This technology has not been a success and many of those affected engines have reverted to timing chains.

What is a timing chain?

Timing chains perform the same basic function but from within the engine. Both the chain and the camshaft/crankshaft sprockets look similar to those on a bicycle.

As with timing chains, the chain must be tensioned correctly. If too loose, the chain risks jumping off the sprockets. Should it be excessively tight, it may break.

What is the difference between a timing belt and a timing chain?

Location

Both timing belts and timing chains are situated on the side of the engine. Yet, timing chains reside within the engine crankcase. Timing belts reside in a separate cover outside the engine - unless they are of Belt-in-Oil designs.

Material

Timing chains tend to be made from steel; the precise grade depends on the engine specification. Some types may possess surface hardening for a longer life.

Timing belts are made from rubber. Dependent on the engine designer's specification, types of rubber employed include EPDM, neoprene, or nitrile. Fabric may be applied to the belt teeth surfaces to reduce friction and enhance longevity. The reinforcement materials used within belts vary too, from fibreglass to Kevlar.

Noise

Both timing chains and belts are designed to operate as silently as possible. This is one reason why some of them run on plastic pulleys, or guides.

Typical lifespan

Timing chains are intended to last the life of the engine. Unfortunately, this is not always the case. The reasons for this vary, from manufacturing/design/material inadequacies, to poor maintenance. Using the wrong lubricant, or neglecting oil changes, is detrimental to timing chain life.

Timing belts are not designed to last the life of the engine. Replacement mileage and time intervals are specified by the car manufacturer.

Cost to replace

As timing belts are designed to be replaced periodically, replacement tends to be easier than a timing chain. Therefore, expect a timing belt change to be less expensive.

Exact costs vary, depending on the vehicle and your local garage labour rates.

When Should You Replace a Timing Belt or Chain?

We cannot provide a definitive timing belt mileage, or time, replacement interval. For instance, they can vary between four years, or 60,000 miles, to 10 years, or 150,000 miles. Yet, you must follow both time and mileage intervals and change the belt kit at whichever comes first. Many garages recommend replacement earlier than the specified intervals, because belts have failed before they are reached.

While belts tend to fail without warning, chains tend to give you some notice. A worn timing chain rattle at idle speeds, particularly immediately after a cold start. Engine misfires can result in bad cases. An engine warning light, or a fault code indicating a timing correlation problem, can also be caused by an elongated timing chain.

You might have heard of situations, where timing chains stretch. This is a misnomer. Chains do not ‘stretch’ - their pins and holes wear and develop slack. Yet, some sophisticated engine management systems can ‘mask’ the early running problems associated with a worn chain.

If you wish to reduce timing chain wear, conduct regular engine oil changes, with a quality oil filter and the correct oil every 6,000 miles, at least.

How Much Does Replacement Cost?

As described earlier, providing accurate costs is not possible. Yet, expect a timing belt change to cost between £350 and £700. Timing chain costs can be at least double, especially if the engine needs removing to gain access.

Consider also that you never replace the chain, or belt, alone. They should be replaced as a kit. Very often, this kit includes ancillary parts, including guides and tensioners. Should the belt run the water pump, expect a garage to recommend that this be renewed as well. Not all timing belt kits include a water pump.

FAQs

What is the average lifetime of timing chains and belts?

Timing chains should last the life of the engine but their life spans are curtailed considerably, if oil changes have been neglected.

Timing belts should last to the first of either the time, or mileage intervals, stated in the handbook. Change the belt sooner, if the car has experienced mainly low-speed, urban driving.

How to tell if your timing belt needs replacing?

Timing belts tend to give very little notice before they fail. If you can remove the top timing cover, look for cracks on the belt surface, or between the teeth. Should you be unsure, have the belt kit replaced at the earliest opportunity.

What tips does GEM have for timing belt and chain replacements?

· Research if your car has either a belt, or chain. Some cars possess gears but this is unusual.

· If your car has a chain and you hear a rattling, or slapping, noise from within the engine, avoid driving the car and consult a garage to inspect the engine as soon as possible.

· Check your service schedule for belt replacement intervals.

· If your chain, or belt, breaks, the engine will likely seize immediately. A car cannot be driven with a broken timing gear.

· Never neglect engine oil and filter changes.

· When handling a new timing belt, crimping it will damage its structure.

· Timing belts will be damaged, if they are levered onto the sprockets. Followed all fitting instructions closely.

· Timing belt and chains replacement tend to require special tools, which we recommend you use.

· Where specified, replace ancillary parts, including any fixings, or bolts.

· Inspect and, if necessary, renew the crankshaft damping pulley, should one be fitted.

· It is prudent to replace the auxiliary front-end drive belt and tensioner at the same time as the timing belt. A broken auxiliary belt can enter the timing belt cover, become entangled and break the timing belt.

· Always use the correct timing belt specification. Never, for instance, use a conventional timing belt within an engine that requires a belt-in-oil type

· Most timing belt changes are performed with a cold engine.

If you have any specific questions about the timing belt, or chain, fitted to your car, GEM's Technical Team can help you. You can send us a technical query, or call 01342 825676 (Mon – Fri, 9am – 5pm).

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