BMW R 68
The BMW R 68 is a two-cylinder motorcycle with 600 cc displacement and 26 kW ( 35 hp ) rated power at 7,000 revolutions / min .. The machine was developed through performance increases from its 600 cc sister model R 67/2. The standard equipment underlined the sporty look of the R68 with narrow front fender, which necessitated a stiffener between the fork legs, as well as by the coupled with the saddle ( and with this off and einfedernde ) special seat cushions, the so-called " race rolls " over the rear fender. The non- folding Zusatzfußrasten were intended not only for ( sporadic ) carrying a passenger, but also allow the rider a smoother racing seat position.
History
In October 1951, the German motorcycle manufacturer BMW revealed at the Frankfurt IFMA a new high-performance model in the style of the work machine of the International Six Day Trial. A top motorcycle, a 160-km/h-Maschine, the fast the predicate " 100 miles Renner " offered the professional world. She was. During their series starting in the summer of 1952 one of the fastest motorcycles in the world and the first production motorcycle that broke the " 100 - mile limit "
Overall, there were three profound facelifts: the middle of 1952 (improved front fork, rubber sleeves ), 1953 ( Knecht air filters and side car port) and 1954 ( full hub wheels, alloy wheels and " torpedo" silencer).
Then was in January 1955 at the Brussels Salon the next generation of BMW's heavy, full swing models presented. The chassis was with these models again on current competition level and so came with the same engine then in 1955 the successor to R 69 out as well with 35 hp from 600 cm3, but in far more stable full swing arm suspension; abruptly fell silent so any criticism of the handling of the fastest BMW.
From the R 68 only 1453 copies were 1952-1954, ultimately because of their exclusivity and the high purchase price of 3950 DM produced.
R 68 Boxer engine
BMW R 68, apparently with modified exhaust system
BMW R 68 (1954 ) with Steib sidecar (1951 )
Technical Description
The engine of the R68 was with other cylinders and substantially revised cylinder heads with larger valves and channels - provided - 38 (instead of 34) mmm intake and 34 ( instead of 32 ) mm outlet. Coupled with the large 26mm Bing carburetors, a sharper camshaft and an increased compression ratio ( 5.6:1 to 7.5:1 by ) the engine power increased from 26 hp to 35 hp. This power is connected to an enormous pulling power in a very quiet engine running, which certainly represented a highlight in the former engine development field.
Once the engine performance of the sports machine has been fully utilized, the weak point of the machine made a detrimental effect: the left on the old stand chassis technology. Compared to international competition, the fast, and very expensive BMW still had no rocker and lost with a totally inadequate Geradweg rear suspension on the rear wheel with bad roads easily contact with the ground. This now unmistakable chassis weakness in interaction with the powerful engine BMW brought a lot of criticism.
The BMW R 68 has an automatic ignition timing on a centrifugal governor. In poor fuel quality, however, the high-density motor tended to fuel ringing ( "Motor ringing "). Therefore, the R68 was additionally equipped with a manual adjustment of the ignition: on the left-hand grip is the Zündverstellhebel. With it, the ignition timing ( angle before the top dead center ) can be adjusted manually. At present, however, a manual correction of the fuel ignition timing is not necessary.
The engine is a longitudinally-mounted two-cylinder boxer, four-stroke engine with the outside through the cylinders in chromed protective tubes running bumpers ( OHVr ). These bumpers actuate the rocker arms in the cylinder head, and that the hanging valves. The camshaft is driven by a current in an oil bath gear train from the crankshaft. The gear oil pump is located behind the front housing cover and is driven by the spur gears via a reduction gear.
The two-cylinder boxer engine of the BMW R 68 rests on two stub axles in a double cradle frame. On the front tail shaft sits behind the aluminum cover, the splash-proof encapsulated DC alternator charge controller. The lead-acid battery sits unenclosed on a rail on the left behind the transmission.
To keep the deflection of the crankshaft at high speed within limits, a special rear main bearing slightly crowned bearing rollers was installed.
On the rear tailshaft the heavy flywheel sitting ( with a visible in the inspection hole ignition marking ) that receives the single dry. The clutch thrust bearing is operated by a push rod passing through the hollow main shaft. This model has the classic curved chrome kick start lever. At the transmission is on the right side in addition a manual shift lever; also this peculiarity of the manual shift option was last built models with the " Gradweg - snapping" and essentially served for quickly finding the Leerlaus. The R 68 has, as the weaker sister models R 51 /3 and R 67 /2, a right-handed propeller shaft with external gear on the shaft drive; in the successor models, the Kardandrehrichtung was changed to left-handed.
The two carburetors are Bing float chamber carburettor with conical needle in a circular slide ( title: 1/26/9 and 1/26/10 ). The wet - air filter element is seated on the gearbox housing. The connection between the air filter and carburetor set chrome intake manifolds without outer rubber elements dar. The air filter is a steel net, which is soaked with oil when the dust settles at the suction of the air, and that is wash and maintenance.
The powertrain has an elastic at the transmission output torque transmitting element, a black textile-reinforced rubber, four- hole disc ( Hardy disc ), which is pushed on Zweifingerflansch the transmission. To transmit the torque of the transmission output shaft to the two finger receiving the propeller shaft. The Hardy disc is equipped with a chrome ring.
The non- encapsulated, chrome drive shaft for the rear-wheel drive is mounted with a universal joint at the angle gear in Alugusskorpus. The reversing gear is a bevel gear with hypoid gearing and 90 ° deflection. The hypoid gears run in a special heavy gear oil for high flank pressures ( hypoid ).