What is it with Swedish brands and installing engines the wrong way around? The Saab 99 famously had a longitudinal engine turned back-to-front in a front-wheel-drive application, and Volvo played around with transverse inline-sixes. While Saab eventually switched to a transverse layout and Volvo eventually went with just four-cylinder engines, Volvo’s last experiment was extra-wonky. Let me explain.
Inline-sixes are smooth, wonderfully-balanced engines that deserve much praise. They’re also incredibly long. That isn’t much of an issue in a longitudinal application like in front-engined rear-wheel-drive vehicles, but Volvo hasn’t built a car on a longitudinal platform since 1998. As such, this new inline-six would have to fit sideways between the strut towers, a total packaging pain in the ass.
To Volvo’s credit, the SI6 engine is remarkably compact for an inline-six, measuring one millimeter shorter than the inline-five that preceded it. However, it was still an incredibly tight squeeze in the engine bays of various Volvo product, which meant that the accessories needed to be flipped around. Yep, Volvo ran parts like the alternator, power steering pump, and air conditioning compressor off the transaxle side of the SI6 engine, a method that shouldn’t really work because there’s no crank pulley on that side of the engine. So how did Volvo pull it off?
Well, Volvo used gears. I take it we’re all familiar with gears, right? One of the key simple machines, these toothed wheels are made to multiply and transmit force when used together, which is exactly what Volvo did to create the READ, short for Rear Engine Accessory Drive, a clever little gearbox on the side of the SI6 engine.
How does it work? Well, drive to accessory and upper engine timing components is the responsibility of two different gears on two concentric shafts that spin at different speeds. This arrangement also takes the load of the accessories off of the top end timing system. If you’re getting flashbacks to the Dodge Viper’s cam-in-cam shenanigans, yes, but also no. Each of these gears is driven by a dual-patterned gear on a shared intermediate shaft. Drive to the intermediate shaft gear is provided by a gear on the crankshaft. Oh, and that gear on the crankshaft also drives the oil pump. YouTube user Smilyeez gives a great look at the READ system in the video above.
The result of all this geared wizardry is that accessory drive is moved up and out of the way of the transaxle, preventing any packaging interference. The downsides? Well, other than the fact that the alternator sits beneath the intake manifold, Volvo didn’t quite get the READ perfect.
As with anything that spins at high speeds, all the READ parts ride on bearings to reduce friction. Unfortunately, every part on a car is a wear item on a long enough timeline, and READ bearings don’t last forever. While a 2007 and newer six-cylinder Volvo emitting a whining noise could just have a bad pulley, that unusual noise has the potential to be far more serious.
In the words of our friends at FCP Euro, the bearing in the main READ gear “commonly goes bad, creating a growling noise from the front of the engine near the alternator pulley. Failure to address this noise can result in gear drive wear and failure.”
I don’t know about you, but failure of a part that prevents your valves and pistons from joining in holy matrimony sounds bad to me. Oh, and because READ parts live within the bowels of the engine, don’t expect repair to be cheap. We’re usually talking deep into four-figure territory. On the plus side, sudden, catastrophic failure is virtually unheard-of, so owners of these engines will at least have some warning that expensive repairs are imminent. Oh, and this engine was also the most reliable powertrain U.S.-based Land Rover owners got in the LR2, so you know, upsides.
Taking a step back for a second, it’s wild as hell that Volvo’s SI6 uses a weird combination of gear-drive and chain-drive to keep the camshafts in step with the crankshaft, but the READ assembly is also an elegantly simple solution to a problem that wouldn’t exist without a little bit of insanity. Keep in mind, Volvo’s previous-generation inline-six didn’t use a crazy READ unit, and that thing fit in early XC90s just fine. Sure, the GM 4T65-E transmission attached to it offered the durability of a Faberge egg, but you know, such was the technology of the time. Regardless, the READ unit is a neat footnote in the history of automotive engineering, and exactly the sort of thing you’d expect from a company that later decided to twincharge most of its model lineup.
(Photo credits: Volvo, YouTube/Smilyeez)
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