INLINE-6 vs. V6?

I am trying to understand why some carmakers (particularly Mercedes-benz) are returning to straight-six engines over V6s. It is common knowledge that it is much easier to balance a straight-six but surely Benz must have had balancing well nailed?

The recently released Benz straight-six does improve on packaging by removing the pulleys on the front end of the engine, but is that reason enough to switch course? I can imagine there must have been lengthy debates as the rm had invested so much in its V6 engines since introducing its rst V6 engine (M112) in 1998. Kudos to BMW for remaining steadfastly committed to the straight-six. JOHAN VISAGIE Stellenbosch

Let’s rst look at the advantages of the V6 engine. The main reason

for the V design is a compact engine that is easy to package. It helped that Mercedes-benz originally used its V8 engine as a base and chopped off two cylinders to keep costs low and allow some parts commonality. The problem with a V6 is vibration as it is not as inherently smooth as an inline-six or even a V8 engine.

The primary reason why Benz made the recent switch is to have a modular engine series going forward. The trend of engine downsizing means the V8 engines would be replaced by six cylinders. The optimum capacity for each cylinder is 500 cm3 for ef ciency and performance. Therefore, there’s already a 2,0-litre, four-cylinder engine and a 1,5-litre, three-cylinder engine from the same series. This could in future include further petrol and diesel derivatives. Such a series is feasible only with an inline design.

BMW has applied this strategy successfully on its petrol engines while Volvo is doing the same for its Drive-e engines sans any six-cylinder variants. The cost advantage of having one modular series of engines is huge and that prompted the direction change for Mercedes-benz. the valvetrain (camshaft and valves). When the vehicle is parked, the excess oil from this region drains to the sump and because the valvetrain is sited at the highest part of the engine, it also receives the oil under pressure last during start-up. Fortunately, a layer of oil remains on the contact surfaces to provide the required lubrication during start-up (and modern oils do have the necessary additive packages). The fact that the dealer stated the noise is normal means other Polos behave in a similar way.