Engine and transmission 30 www.aftermarketonline.net SEPTEMBER 2025 Belt had to function in chemically aggressive environment for engine’s entire service life Rethinking tech for higher engine performance Belt-in-oil technology — a crazy idea, but an inspired one! Although some might question the validity of the belt-in-oil (BIO) concept, preferring a traditional chain drive system, several vehicle manufacturers (VMs) including Ford, PSA and VAG have embraced the technology. In this Aftermarket article, Dayco, the company that pioneered BIO on behalf of multiple VMs, shares the story behind the development of the oil pump belt in the 1.6 litre TDI engine used in millions of VAG vehicles. With emissions reduction and weight saving as key goals, the oil pump, historically chain driven, became the focus. The aim was to retain the same layout with fixed centre distances and deliver the same function, but without using a tensioner. The new solution had to meet several key requirements: O No redesign of the drive; O No change to the assembly line; O Maintain or improve performance; O Meet lifetime targets; O Offer a cost advantage. Using the original chain layout and surrounding geometry, the belt system was developed to match. The driver pulley was a sintered part, press fitted onto the crankshaft without flanges. The driven pulley, also sintered, was fitted to the pump shaft with two flanges. The system worked without a tensioner, reducing complexity and potential points of failure. Before the design could be approved, Dayco carried out feasibility studies on both the layout and the belt. The oil pump is secured to the lower engine block by screws and located with reference bushings. Axial tolerances on both the camshaft and oil pump were analysed. A belt width of 9.4mm was chosen, and parts were manufactured to test extreme tolerances through fitting and validation. Radial tolerances were then assessed, and a nominal belt length was defined. Conventional timing belts are designed to operate in dry conditions. For BIO, the belt had to function in a chemically aggressive environment throughout the engine’s entire service life and across various global climates. This demanded a new material strategy. Experience from sealing components cannot be transferred, as belts are exposed to dynamic mechanical stress. The development phase involved extensive variables, including more than 100 different engine oils diluted with fuel, water, acids, and cleaning fluids, at varying temperatures and levels of ageing. Accurately defining real world conditions was essential. With the support of oil manufacturers and VMs, Dayco created a test matrix. To validate performance, Dayco developed a focused testing procedure to simulate contamination and evaluate key belt parameters. Samples were soaked in oil and fuel to track degradation. Time and temperature of exposure produced a damage factor for each tested parameter. Controlled measurements included elongation, tensile strength and modulus. Using these metrics, engineers could calculate the number of hours equivalent to full-service life. To accelerate testing, oil temperatures were raised. In addition to passing the standard VM validation process, Dayco created bespoke tests to assess chemical and mechanical wear. Switching from a chain to a belt reduced the power required to drive the oil pump, particularly at lower oil temperatures. Testing and modelling confirmed this was mainly due to reduced internal friction and the removal of sliding tensioning components. This early development of BIO technology enabled Dayco to expand the solution to other engine platforms. Workshops repairing BIO equipped vehicles must ensure technicians are aware of the potential challenges, know what to look for, and are trained in the correct replacement procedures. Email info.uk@dayco.com or visit: www.dayco.com for more information and training support.
RkJQdWJsaXNoZXIy MjQ0NzM=