Which is better? Timing belts or timing chains?
Popularised by overhead camshafts appearing on road car engines from the 1970s, the once durable last-for-life timing chain was replaced by an externally-mounted replaceable timing belt, which also synchronised the engine crankshaft movement with that of the camshaft, to ensure that the valves and pistons did not make sudden, unexpected and violent content. If you are a non-technical reader and have made it this far into this blog, the result of that occurrence is a ruined engine and a hideously large repair bill.
As belts became almost universal by the late 1990s, buyers had become accustomed to budget for the mandatory timing belt replacement interval, which tended to be set by over-optimistic car marketing departments, much to the annoyance of owners, many of whom were faced with unexpected bills, when the part failed prematurely.
If the belt lasted to its replacement interval, dependent on the make-and-model, the belt’s tensioners and the engine water pump would need replacing, too. The result was a bill totalling between £250 and £400, which was considerably less than the several thousands of pounds required to replace (or recondition) the engine, in the event of belt breakage. When it was realised that not having a belt could reduce maintenance bills and increase sales, the chain became popular again.
Unfortunately, the modern timing chain appears to be somewhat less resilient than its ancient forebear. No longer should you presume that a ‘belted’ engine is inferior.
The use of lightweight metal chains, plastic guides and tensioners that rely on oil pressure to work (which become less effective, because of the very long oil change intervals that modern cars possess) has resulted in a variety of makes-and-models suffering from either damaged engines, or (if caught early enough), needing a complete timing chain assembly within the engine’s serviceable life-span, which tends to be far more involved and expensive, when compared to the equivalent timing belt kit replacement.
As the timing chain is situated within an engine, rather than being mounted adjacent to it, like a belt, accessing the chain dictates that the engine has to be dismantled partially, or, in some cases, removed from the car and stripped-down. In my experience, the most common engines to suffer from timing chain failure include various iterations of the Volkswagen Group TSI petrol unit, the Peugeot / BMW ‘Prince’ petrol engine used on the MINI and various Peugeot and Citroën models, plus a number of four and six cylinder BMW petrols and diesels. Pictured, for example, is a new timing chain assembly being lowered into a N47 1.8-litre petrol engine from a 32,000 miles 2008 BMW 1 Series.
If you are looking to buy a car equipped with a timing chain, check first if the model in question is prone to chain failure (GEM members can call or e-mail our Technical Team). If so, see if there have been any manufacturer recalls. If there is a recall, check that the work has been carried out. If not (and some carmakers act in denial in respect to their timing chain longevity), enquire if the manufacturer is offering a reduced cost timing chain replacement at its dealerships.
If the carmaker will not help with replacement and you are buying from a trader, query to see if the used car warranty covers timing chain kit renewal. You may wish to take-out a separate warranty to provide extra peace of mind subsequently, should the part need replacement soon after you have taken ownership.
A worn timing chain can make its presence known by rattling at idle speed, particularly immediately after a cold start, or even causing an engine misfire in bad cases. An engine warning light, or a fault code indicating a camshaft timing issue, can also be caused by an elongated timing chain (note, chains do not ‘stretch’, their pins and holes wear and develop slack). Yet, some sophisticated engine management systems can ‘mask’ the running problems associated with a worn chain.
If you are looking to reduce timing chain wear, the best advice to follow is regular oil changes, using a quality oil filter every 6,000 miles, at least.
Read our article on replacing your timing belt.