The fifth generation of BMW's four-valve boxer engine will make its debut in the new R 1250 GS and RT. The latest evolution of its liquid-cooled boxer features increased capacity, more power and introduces a new ShiftCam variable valve lift and timing system for the first time in a BMW motorcycle.
The two-cylinder boxer engine has been a part of BMW Motorrad's history since its first ever model, the 1923 R 32. After several decades of two-valve, air-cooled variants, BMW introduced a four-valve, air/oil-cooled boxer in 1992 with the R 1100 RS.
Two years later this motor powered the R 1100 GS, the emblematic model that ushered in a new era for large-capacity adventure motorcycles. Since then, BMW has rolled out four more generations of its iconic motor, starting with the 1150, the 1200 and, in 2012, the 1200 LC, which introduced a hybrid setup, with a liquid-cooled engine block and air-cooled cylinders.
For 2019 BMW retains the same air/liquid cooling architecture in an extensively redesigned boxer engine that grows in capacity by means of both longer piston bore and stroke, up from 1,170 to 1,254 cc.
The new engine features a novel valve train that BMW calls ShiftCam, and is in fact a variable valve lift mechanism. Applicable only on the intake valves, it relies on a camshaft that hosts dual sets of lobes of different lift for each valve.
A slotted gate on one side of the camshaft is connected to an electronic motor that slides the cam axially in order to position the appropriate lobe above each intake valve rocker arm. The short lobes provide shorter valve lift and duration when the engine works in low revs, while the longer ones will better accommodate full-load conditions.
Also, BMW has arranged the two intake lobes of each cylinder with a small angular offset on the cam, so that their timing is asynchronous. As the two intake valves open at different degrees, the fuel enters the combustion chamber in a swirl, making for a more efficient burn.
According to BMW, the motor produces more torque all through the rev range; from 2,000 up to 8,250 rpm there's always more than 110 Nm (81 lb-ft) available. The new boxer's peak output measures 136 hp (100 kW) at 7,750 rpm and 143 Nm (105.5 lb-ft) at 6,500 rpm, (the previous motor would do 125 hp (92 kW) and 125 Nm (92.2 lb-ft) at exactly the same rpm), and also suggests a four percent reduction in fuel consumption.
In terms of weight, the new model tips the scales at 249 kg (549 lb) in road-ready form, which is some 5 kg (11 lb) more than the previous R 1200 GS.
The 2019 engine incorporates a new exhaust system, updated BMS-O engine control unit, a slipper clutch as standard, improvements in lubrication and cooling, a quieter toothed (HyVo) timing chain, and the incorporation of two knock sensors that should be greatly appreciated by those that venture to places where low RON gasoline may be the only available option.
BMW also updates the GS' electronic equipment with two riding modes (Road and Rain), Automatic Stability Control (ASC, BMW's basic traction control), and Hill Start Control (HSC) as standard. The optional electronic gear that can be loaded on the 2019 R 1250 GS is extensive, with several Pro packages for almost everything, from riding modes and ABS, to dynamic traction control and even brake assist, allowing the rider to fine tune the motorcycle.
All these can also be complemented with BMW's Dynamic ESA that electronically adjusts the suspension's damping characteristics in real time according to the riding conditions, as perceived by the bike's sensor array.
Finally, the new GS receives a brand new 6.5-inch color TFT display with Bluetooth connectivity as standard.
One thing that doesn't change in the R 1250 GS is its looks. The design remains almost identical to the existing R 1200 GS, with only some new color schemes and a few details that reveal it's the 2019 model – such as the front side panels, the cylinder head covers and, obviously, the small 1250 decals on the fuel tank.
Most of the GS model changes are carried on to the 2019 R 1250 RT as well. The boxer-engined touring machine gets the new ShiftCam motor with the same gearing and performance figures as in the GS, while keeping its design largely unchanged.
The new RT also receives two riding modes, ASC and HSC as standard, and can be updated with the full electronic arsenal from BMW's long list of extras, including the Dynamic ESA, which wasn't available for this model previously.
See the new ShiftCam technology in detail in BMW's video below.
Source: BMW R 1250 GS and R 1250 RT