On the move: the BMW GS conversion by BMW developer Laszlo Peres

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On the move: the BMW GS conversion by BMW developer Laszlo Peres
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On the move: BMW GS conversion

The BMW GS from BMW developer Laszlo Peres

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Former BMW developer and off-road specialist Laszlo Peres gets his classic boxer going, in the spirit of historical off-road sport.

He just can’t help it. In his well-deserved retirement for three years, Laszlo Peres is passionately tinkering and constructing his variant on the subject of off-road boxers. Like almost all of his former employees from the BMW test department, he is also addicted to the GS boxer skin and hair. In the 70s and 80s he was one of the BMW technicians who conjured up the series-ready R 80 G / S from the first prototype, the “Red Devil”, and thus probably also saved the BMW motorcycle division. Last but not least, the off-road successes of Herbert Scheck, Kurt Fischer, Richard Schalber, Rolf Witthoft and Laszlo Peres were the decisive factors in putting the standard R 80 G / S on wheels.

D.But Laszlo Peres had already implemented completely different high-displacement off-roaders. He built a 760 cm³ Maico single-cylinder two-stroke engine and, not to forget, a self-made four-stroke engine with two-stroke crankshaft housing and mixed lubrication, which he of course also tried out in off-road sports and still uses today in classic off-road driving.

Back at the BMW boxer, the tinkerer set about realizing what had been forgotten in the standard GS models: consistent lightweight construction. He starts with the question of the purpose. Does a big enduro really have to be able to do everything in the classic sense? The clear answer: no. Because there are plenty of cargo donkeys and long-distance machines; light, robust mountain goats unfortunately less and less. So Laszlo Peres grabbed exactly the machine that served as the basis for the R 80 GS-Basic. And if it’s not only to be light, but also narrow and delicate, it is best to start with the engine. This is why the drive is based on the substructure of the R 65, which with a stroke of only 61.5 mm (R 80 GS: 70.6 mm) provides ideal conditions for a more compact structure. The configuration of the short-stroke shaft and HPN piston / cylinder unit saves around 25 mm in overall width on each side compared to the R 80 GS. The driver notices the difference in the fact that he does not come into disruptive contact with the Bing carburetors in the typical terrain, far forward sitting position.

So that the boxer retains its full punch despite the short-stroke design, 97 mm pistons are inserted in the Nikasil-coated light metal cylinders. This results in a displacement of 910 cm³ which guarantees high revving and is good for 75 hp at 7000 rpm and 85 Nm at 5500 rpm.


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Plain and simple: the off-road boxer is optically and technically reduced to the original values ​​of an enduro.

It is no surprise that the detailed work is carried out in a BMW engine modified by Laszlo Peres: he milled off the engine housing above the crankshaft, which is beneficial on the one hand to the weight, on the other hand to the performance and durability at high temperatures. "A real heat build-up occurs in the cast bell, which leads to high oil temperatures and a noticeable loss of performance", the thoroughbred technician explains the radical measure. Another advantage: The carburettors get cool, performance-enhancing intake air from the now free-standing air filter housing, which is decoupled from the gearbox. The two-valve heads compress the mixture to 10.5: 1 (series R 80 GS: 8.2: 1).

The compact ignition / alternator unit from PVL (www.pvl-zuendung.de) replaces the standard alternator. Its ignition curve can be adjusted to the thermal conditions of the engine in order to squeeze the best possible performance and stability out of the boxer.

The small company SR has also committed itself to this task (www.sr-racing.de), which tailored the Peres boxer with a slim, light and yet TÜV-compliant exhaust design. Thanks to the single-sided swing arm, the muffler hugs the rear wheel, which is equipped with an HPN hub. To protect the oil pan from massive damage from rocks or rubble, it has an exchangeable aluminum base plate fastened with countersunk screws.

For the changes to the chassis of the GS, Laszlo Peres looked around the BMW parts store and installed the Paralever swing arm of the R 1100 GS. He equipped the mono spring strut with a self-designed travel-dependent damping.

At the front, an upside-down fork keeps the 21-inch front wheel on track, which is braked by two 245 mm discs and Brembo floating caliper calipers. The tank, seat and plastic parts adhere to the contemporary lines and give the Peres-BMW the lightness of a classic enduro from the 70s and 80s.


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Retirement: Laszlo Peres is not only passionate about BMWs.

The result of the many small modifications can not only be seen and heard, but also felt. The boxer is there at the push of a button, but carries a kick starter for a walk just in case. The BMW engine releases its idle speed smoothly and smoothly and cranks its way through the rev range with a beautifully linear power development. The boxer spontaneously implements every gas command without nervously tugging at the rear wheel. This helps a lot when going off-road and provides plenty of traction when it matters.

As the speed increases, all inertial forces that act in the engine seem to dissolve into thin air. If the engine still vibrates back and forth in the frame, as is typical of the Boxer, in the lower speed range, the vibrations smooth out in the finest way up to maximum speed. Many a new four-valve boxer engine cannot simply attest to this virtue. In general, well-groomed manners characterize the Peres BMW. If the Ur-GS can already impress with its excellent handiness, the lightweight construction goes one better.

Tight hairpin bends, changes in lean angle, curves with all the radii and arcs in the world, the Peres GS follows every steering impulse without hesitation and with stoic calm. This is of course partly due to the tight spring elements, which take their toll when driving over joints and rough asphalt faults; Comfort is different. But as I said, an enduro doesn’t have to be able to do everything.

Technical specifications


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Short-stroke, slim-built boxer based on the R 65 with 75 hp and a silky smooth engine run.

engine design type  Air-cooled two-cylinder four-stroke boxer engine with an underlying camshaft; two valves per cylinder, operated by push rods and rocker arms
Base  Engine housing of the BMW R 65
drilling  97 mm
Hub  61.5 mm
Displacement  910 cm3
compression  10.5: 1
power  75 hp at 7000 rpm
Torque  85 Nm at 5500 rpm
Mixture preparation  two Bing constant pressure carburetors, Ø 32 mm
 
Power transmission
coupling  Dry clutch
transmission  Five-speed gearbox, claw shift
Secondary drive  propeller shaft
  landing gear Base  R 100 GS double loop tubular frame
Front wheel guide  Upside-down telescopic fork, Ø fork inner tube 43 mm
Rear wheel guide  Paralever swing arm of the R 1100 GS, central spring strut with travel-dependent damping
Front suspension travel  245 mm
Rear suspension travel  245 mm
bikes  Wire spoke wheels with aluminum rims
Front brake  Double disc brake Ø 245 mm, Brembo double piston calipers
rear brake  Disc brake of the R 1100 GS, Ø 265 mm
  mass and weight wheelbase  1543 mm
Steering head angle  62 degrees
trailing  118 mm
Weight  202 kg with tools and fuel
Weight series R 80 GS  225 kg with tools and fuel

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