The latest development – belt-in-oil
Ten years ago, in response to car manufacturers’ demands to reduce weight and exhaust emissions wherever possible, Dayco introduced the belt-inoil (BIO) timing belt. Presented first on the Ford Lynx 1.8-litre TDCI, the BIO timing belt replaced earlier engines’ Duplex chains, tensioners and sprockets with a special oil-resistant belt that comes pre-assembled with its own tensioner and pulleys. Unfortunately, customer experience with this specific application has not been as positive, compared to the earlier maintenancefree chain. As with dry timing belts, the teeth are prone to stripping but, as the BIO belt is situated within the engine, the fragments can work their way into the oil pump, or else block the oil pump strainer within the sump. Any low oil pressure warnings, or difficulty in building pressure immediately following a cold start, might indicate a BIO problem.
Our technical partner for this article, TLC Ford of Wolverhampton, reports that many customers insist on making a belt-to-chain conversion to provide a life-long solution. Best of all, this task is simply a bolt-on conversion that is detailed later in this feature.
Given their drawbacks, one might presume that BIO belts are classed as an expensive mistake never to be repeated, but you would be wrong. The Ford Ecoboost 1.0 Fox engine, for example, has a timing belt running in 0W20 oil, while both Peugeot-citroën and the Volkswagen Group have adopted BIO systems also in their small-capacity
engines. However, these units are very new and only time will tell whether BIO timing belts are as dependable as many car-makers claim, especially given long service intervals and the proliferation of stop-start systems, both of which place extra strain on the belt. Speaking to the motor trade press, Herman Schulte, head of timing belt development at Contitech, said that BIO technology was necessary to help car-makers meet their 2020 CO2 targets of 95g/km, as well as making the timing gear lighter and more compact. Comparing both the original Duplex chain design with the BIO belt for Ford’s 1.8-litre TDCI (see Step 26), the latter is considerably lighter and likely to be significantly cheaper to produce.
If working on cars with variable valve timing, be wary of any extra work required, such as additional instructions to unload the hubs. Consider also replacing any worn hubs, while the timing belt is being renewed.