Timing belt in oil (BIO) overview

Posted on September 25th, 2017 by Rob Marshall


One of the driving forces in modern car development has been to enhance efficiency wherever possible, while reducing tailpipe emissions, including CO2. Some GEM members have questioned if some of these systems just pay lip-service to official emissions and fuel consumption data that have altogether less relevance in the real world. Automatic stop-start is one such technology that springs to mind in the question about whether, or not, the fuel savings are sufficient to cover the costs of addressing the extra stresses meted-out to the engine, timing gears, electrics and more expensive batteries, which are all stomached by the car owner as the car ages.

2017 sees the tenth year in which Belt In Oil (BIO) timing belts were introduced on a production engine; the Ford 1.8TDCi motor. Earlier iterations of this unit used a duplex chain assembly, which connected and synchronised the crankshaft and diesel pump sprockets. They lasted the lifetime of the engine but this is not the case with the belt. The BIO fitment is seen as vital in reducing CO2 emissions and driving engine efficiency. However, we have heard of a number of them failing in service over the last few years and the issue has become so well-known that some owners have requested that independent Ford specialists should convert the belt back to a chain, which is a simple bolt-on conversion.

While a failed BIO timing belt can have the same ramifications as a failed dry timing belt, in that piston and valve gear damage is most likely, BIO failure can cause even more harm. As timing belts tend to shed their teeth, rather than snap, the fragments from the BIO belt can find their way into the oil pump on the Ford engine, which is fitted within the front engine case. If this does not reduce (or cut) oil pressure, the fragments can block the oil pump strainer within the pump. Naturally, this can damage other parts of the engine, too.

As BIO timing belts have been employed subsequently on a number of new-generation small-capacity engines, we wonder how reliable they will be in the longer term. Ultimately, we hope that that the customer is not the one to be saddled with expensive bills, when the parts that have been designed for an environmental benefit fail prematurely.