BMW Motorrad

The F Series of single-cylinder BMW motorcycles was first launched in 1994, as the F650, and was built by Aprilia around a carbureted 650 cc four-stroke, four-valve, single-piston engine, and chain drive. The mission for the F 650 was to provide an entry level BMW motorcycle. In 2000, the F650 was redesigned, now with fuel injection, and labeled the F650GS. An off-road focused F650 Dakar model was also launched that year. 2002 saw the addition of the F650CS 'Scarver' motorcycle to the line up. The Scarver was different from the F650GS variants in that it utilized a belt drive system opposed to a chain, had a much lower seat height, and was intended for on-road use. All F650 motorcycles produced from 2000 to 2007 used a 652 cc engine built in Austria by Rotax and were built by BMW in Berlin.

In late 2006, the G series of offroad biased bikes motorcycles was launched using the same 652 cc engine fitted to the F650GS, although that engine is no longer manufactured by Rotax. The latest version of the 652cc single engine fitted in the new G650GS is now produced in Berlin after 2 years production in Loncin, China.

In November 2007, the G450X sport enduro motorcycle was launched using a 450 cc single-cylinder engine. The G450X contained several technological improvements over the Japanese off-road racing motorcycles but the most unusual and significant was the use of a single pivot point for the drive sprocket and the swing arm. This unusual configuration allowed for a very tense drive chain with no slop and eliminated acceleration squat. The former benefit saves on chain and sprocket wear and the latter allows for a more consistent drive geometry and fully available rear suspension travel during heavy acceleration.

In mid-2006, The F Series added two new motorcycles to the lineup, the F800S sports bike and F800ST sports tourer, both which use a 798 cc parallel-twin engine built by Rotax. Both motorcycles also feature a belt drive system similar to what was in use on the F650CS. In 2007 the single-cylinder F650GS was replaced with the twin-cylinder F800GS and F650GS models. The latter uses a de-tuned version of the 798 cc engine fitted to the F800GS,[14] marking a departure from BMW's naming convention.

Four different BMW airhead and oilhead valve covers

1954 R68's two-fin valve cover

The R series are built around a horizontally opposed flat-twin (boxer) engine. As the engine is mounted with a longitudinal crankshaft, the cylinder heads protrude well beyond the sides of the frame. Originally, R series bikes had air-cooled heads but are now produced only with partial oil cooling or water cooling. The type of internal combustion engine cooling used across the various R series engines leads to the use of the distinguishing names airhead and oilhead.

Airheads are BMW motorcycles with an air-cooled vertical-single or horozintally-opposed twin engine that were built from 1923 to 1995. Most airheads made from 1969 to 1995 used the BMW 247 engine, although 248/1 engines were used on mid-sized R-series motorcycles from 1978 to 1993. Even high-performance motorcycles, such as the R90S used the 247 engine; and its successor, the R100RS, was fitted with an oil cooler.

An "Oilhead" is a name to describe BMW flat-twin motorcycle engines with partial oil-cooling, and to distinguish these engines from the earlier air-cooled "Airhead" models.[15] The Oilhead's finned cylinders have conventional air-cooling, but the four-valve cylinder-heads are oil-cooled. Unlike earlier BMW boxers which had a single camshaft in the crankcase (variously above or below the crankshaft), the Oilhead has a camshaft in each head. (It is still technically an overhead valve engine rather than a true overhead camshaft unit, as the camshaft bears onto very short pushrods which operate valve rockers). In 2013, BMW introduced water-cooling to its boxer range.[16] The engine is still used in the BMW R nineT[17] line of motorcycles.

In April 2020 BMW launched its cruiser BMW R18 with BMW's largest boxer engine featuring 1,802 cc (110.0 cu in), 90 hp (67 kW) and 158 N⋅m (117 lbf⋅ft).[18]

From 2013 (R1200GS), some BMW bikes have water-cooled heads, but (like the oilheads), the new engines still use air-cooling for the cylinders. Approximately 34% of the cooling is attributed to the water-cooling which is concentrated in the highest heat-generating areas such as around the exhaust-valve seats, etc.

The inlets are now on top of the cylinder (not behind as before) and the exhausts are below (no longer in front).

Between the introduction of the R39 in 1925 and the discontinuation of the R27 in 1967, BMW made motorcycles with single-cylinder engines. These were similar in design to their larger flat-twin motorcycles, including the use of shaft drive, but the engine was mounted vertically within the frame.[19]

The K series BMWs have water-cooled engines of three (K75), or four (K100, K1100, K1200, K1300), or six (K1600) cylinders. Up until 2004, all K series engines, whether three or four cylinders were that of the original "flying brick" layout, so called due to the external appearance of the engine. The layout of these original K engines is unique within motorcycling in that the engine is mounted lying on its side, with the crank on the right side of the bike and the cylinder heads and valve gear on the left. This format had the advantage of allowing the drive system to have only one 90-degree translation within the final drive housing, potentially reducing drive train losses. All of the original format K engines were also mated to a dry automotive-type clutch. The uniform use of the traditional K engine ceased with the K1200 models in 2005, with a new 1200 series engine that was radically different from the flying brick in that it was a conventional transversely 55-degree slant-mounted four-cylinder engine coupled to a wet clutch and a unitary construction gearbox. It was at this time also that the K bike shaft drive moved from the right side to the left. Despite this new engine, the traditional flying brick K engine continued in service with the giant K1200LT luxury touring bike until 2009, at which point the flying brick bowed out along with the K1200LT. This was the event that presaged the development of the ultimate K engine in terms of size and complexity, the six-cylinder K1600 series fitted to the K1600GT and GTL models.

BMW K100 motorcycle engine circa 1986

The first K-series production bike was the K100, which was introduced in 1983. In 1988, BMW introduced the K1 which had the Bosch Motronic fuel injection system.

From 1985 to 1996, the K75 740 cc three-cylinder engine was produced.

In 1991, BMW increased the displacement of the K100 from 987 cc to 1,097 cc and the model designation became the K1100. The K1100LT was the first with the new engine displacement. In 1998 BMW increased the size again to 1,170 cc. This upgraded flat-four engine appeared in the K1200RS. This engine continued in production for the K1200LT range, with a power-boosting update in 2004, until the end of the LT production run.

The later K1200 engine is a 1,157 cc transverse inline-four, announced in 2003 and first seen in the 2005 K1200S. The new engine generates 123 kW (165 hp) and is tilted forwards 55 degrees. It is 43 cm (17 in) wide, giving the bikes a very low center of mass without reducing maximum lean angles.[20]

In October 2008, BMW announced the new K1300GT, K1300S and K1300R models, all of which feature a larger capacity 1293 cc engine producing up to 175 hp (130 kW). The new engine produces maximum power output 1,000 RPM lower than the previous engine, producing more torque due in part from a butterfly flap fitted in the exhaust.

In 2011, BMW launched the K1600 range—the K1600GT and K1600GTL—featuring a new 1,649 cc (100.6 cu in) straight-six engine, which is mounted transversely across the chassis.[21] The engine is angled forward by 50°.[22] The engine was originally used on the Concept 6, a concept bike that was shown at the 2009 EICMA Milan Motor Show.[23] BMW claims that the engine at 560 mm (22 in) wide, just 67 mm (2.6 in) wider than the K1300 engine,[22] is the narrowest six-cylinder engine ever produced. Cylinder bore is 72.0 mm (2.83 in) and the distance between cylinder centres 77 mm (3.0 in).[22] The camshaft is hollow, with cam lobes pressed on, which saves around 2 lb (0.91 kg).[24] The engine has electronic throttle control and multiple drive modes which can be set according to road conditions.

The first BMW monolever suspensions appeared in 1980 on the then-new R80G/S range. It had a single universal joint immediately behind the engine/gear-box unit. This system was later included on updated versions of the K & R Series.

Paralever is a further advance in BMW's single-sided rear suspension technology (photo right). It decouples torque reaction as the suspension compresses and extends, avoiding the tendency to squat or rise under acceleration and reducing tyre chatter on the road surface. It was introduced in 1988 R 80 GS and R 100 GS motorcycles.

Revised, inverted Paralever on a R1200GS

In 2005, along with the introduction of the "hexhead", BMW inverted the Paralever and moved the torque arm from the bottom to the top of the drive shaft housing (photo right). This reduces underhang of components and tends to increase ground clearance in right lean.

The term "Paralever" is a portmanteau word from "Parallelogram" and "Lever". The "lever is the swinging arm; and the "parallelogram" is the shape between the four elements of the rear suspension (rear drive, drive shaft, transmission, and lower or upper brace). Other motorcycle manufacturers have patented similar designs, including Arturo Magni for MV Agusta and Magni-Moto Guzzi machines, and Moto Guzzi's Compact Reactive Shaft Drive.

In 1935, BMW fitted the first mass-produced hydraulically damped telescopic fork to its R12 and R17 motorcycles. BMW still uses telescopic forks today on its F-series, G-series, HP, and S1000RR motorcycles.

The R-series, which had used only the Telelever and the Duolever front suspensions for several years, has partly returned to telescopic forks in the 2015 model year with the introduction of the R 1200 R and R 1200 RS.[30]

Earles fork on a BMW R60/2

Englishman Ernest Earles designed a unique triangulated fork that, unlike telescopic forks, resists the side-forces introduced by sidecars.[31][32][33] BMW fitted the Earles fork to all its models for 14 years from 1955. In the event, this was the year that use of sidecars peaked and quickly fell off in most European markets (e.g. the UK) but the Earles fork system was well liked by solo riders too. It causes the front end of the motorcycle to rise under braking — the reverse of the action of a telescopic fork. The mechanical strength of this design sometimes proved to be a weakness to the rest of the motorcycle, since it transfers impact pressure to the frame where damage is more difficult and expensive to correct.

BMW's Telelever front suspension on a R1150R

Developed by Saxon-Motodd in Britain in the early 1980s, the Telelever fork aims to improve handling stability during cornering and braking. The Telelever uses conventional telescopic forks, but the stanchions contain only lubricating oil. Springing and damping functions are dealt with by a monoshock attached to a "Telelever" wishbone. The wishbone pivots on the front of the engine block, and the wishbone's forward end is attached via a rose-joint to a brace connecting the fork sliders. As there is no lower triple clamp, the fork sliders are longer and lighter than on a conventional telescopic fork, and the greater slider/tube overlap reduces both torsional flex and unsprung weight.

The Telelever system's main benefit is that it separates the steering function from the braking and suspension functions Braking forces are taken back via the wishbone, thereby eliminating brake dive. During braking, the trail and castor angle (rake) increases instead of decreasing as with traditional telescopic forks. Some riders used to conventional forks reported that the Telelever can initially lack "feel", and that the absence of dive is initially disconcerting;[34] but the R1100S BoxerCup Replika (a model with its own race series) shows that the Telelever fork provides responsive and predictable handling.[15][35]

The term "Telelever" is a portmanteau word from "Telescopic fork" and "Lever"; the "lever" being the wishbone arm.

The top of the Duolever suspension

In 2004, BMW announced the K1200S, incorporating a new front suspension based upon a design by Norman Hossack.[36] BMW recognised this fact but paid Hossack no royalties.[37] BMW named its new front suspension the Duolever. As of 2018, the Duolever has been used on all K1300 and K1600 models.

The official BMW Motorrad explanation of the duolever includes this:[38]

The advantage of this front wheel suspension on the motorcycle market at present is its torsional rigidity. The BMW Motorrad Duolever front wheel suspension is not influenced by negative forces in the same manner as a conventional telefork whose fixed and take-off tubes twist laterally as well as longitudinally during jounce/rebound and steering. Its two trailing links absorb the forces resulting from the jounce/rebound and keep the wheel carrier stable. Thus, any torsioning is excluded and the front wheel suspension is very precise. The steering commands of the rider are converted directly and the feedback from the front wheel is transparent in all driving conditions.

A kinematical anti-dive effect is additionally achieved, just as for the Telelever, due to the arrangement of the trailing link bearings. While a conventional telefork during strong braking manoeuvres jounces heavily or locks, the Duolever still has sufficient spring travel remaining in this situation and therefore the rider can still brake into the corner extremely late yet directionally stable.