BMW R 28
Allgemeine Informationen
Foto aus "BMW Einzylinder richtig angefasst" (S. 154 Bild 15) von Ernst "Klacks"Leverkus. Einer von drei Prototypen der R 28. Als Kundenkreis waren hauptsächlich Behörden angepeilt. Es gab 3 verschiedene Prototyp-Ausführungen: R28a mit Langarm-Vorderradschwinge, R28b mit Kurzarm-Vorderradschwinge und die R28c mit Telegabel, wie sie später in den großen /5 Modellen verbaut wurde. Das Projekt wurde dann aber gestoppt, weil niemand mehr Einzylinder haben wollte.
Zitat:
The BMW R28 is a development of the production touring motorcycle model R27 for the requirements of the Defense Ministry, Frontier Guards and Cross Country sports enthusiasts. I understand that all vehicle specifications for the Military were achieved except for the weight and it appears likely that BMW was not prepared to design a totally new motorcycle without guarantees of getting the order from the authorities. Several versions of the R27 were also tested with normal Earles Forks, modified Earles Forks and with telescopic forks. Some of the spec. required: Frame with rear wheel suspension; Telescopic fork; Cross country tyres; Suitably large fuel tank; Seating for 1 - 2 persons; Sturdy sump guard; Oil moistened air filter (oil bath?); Brackets for two panniers; Holder for dispatches; High level exhaust system (Note the photo shows a low level system fitted).
Folgende Tabelle wurde entnommen bei: www.bmbikes.co.uk/specpages/R28.htm
| Start of Production | 1964 | |
| End of Production | 1964 | |
| Numbers Produced | Pre Production only | |
| Engine | ||
| Motor Type | Modified production single cylinder engine: vertical air cooled 4 stroke. Aluminium crankcase, cast iron cylinder, aluminium cylinder head with inclined valves. Built-up steel crankshaft with self aligning ball and roller main bearings. Chain drive with tensioner for ball race mounted camshaft. Valve operation by pushrods and rockers. Anti vibration flexible engine mountings | |
| Bore x Stroke | 68 x 68 mm (2.67 x 2.67 in) | |
| Displacement | 245 cc | |
| Max Power | 18 hp at 7,400 rpm | |
| Compression Ratio | 8.2 : 1 | |
| Valves | OHV | |
| Carburation System | Rubber mounted slide type carburettor with long inlet tract and waterproof enclosure. Oil damped air filter | |
| Engine Lubricating System |
Lubrication by gear pump in sump | |
| Power Transmission | ||
| Gearbox | In unit with engine. Gears with robust sliding dog engagement and shock absorber | |
| Clutch | Single plate dry clutch with diapragm spring | |
| Number of Gears | 4 | |
| Shifting | Foot lever | |
| Gearbox Ratios | 5.33 / 3.02 / 2.04 / 1.54 | |
| Rear Wheel Ratio | 4.5 : 1 | |
| Rear Wheel Drive | Cardan shaft fully enclosed in oil bath swinging arm with heavy duty rubber sealing. Maintenance free spiral bevel gears with constant tooth angle | |
| Electrical System | ||
| Battery | 6 volt 12 amp hour | |
| Alternator | 90 watt alternator mounted on front of crankshaft. Vibration free voltage regulator | |
| Ignition | Centrifugal ignition advance mechanism. Camshaft driven contact breaker | |
| Misc. | 160 mm diameter headlamp with parking lamp, lighting switch and tachometer. Combined tail / brake / number plate lamp. Horn, trafficators | |
| Chassis | ||
| Frame | Closed, electric welded double loop frame of steel, particularly suitable for high speed use. Taper roller steering head bearings | |
| Front wheel suspension | Telescopic forks (developed from BMW R25/3) with hydraulic damping and travel of 126 mm. | |
| Rear wheel suspension | Rear swinging arm with two maintenance free taper roller bearings and hydraulic dampers. Travel of 105 mm. Short wheelbase and high ground clearance | |
| Misc. | High level cross country type handlebars with clutch and brake controls. Sports handgrips. Friction steering damper. Foam dual seat for 1 - 2 persons | |
| Wheels | Full width aluminium hubs with steel brake linings | |
| Wheel rims | 2.15B x 18 rims | |
| Tyres, Front | 3.25 / 3.50 x 18 Cross Country | |
| Tyres, Rear | 3.25 / 3.50 x 18 Cross Country | |
| Brakes, Front | Drum brake 160 mm x 35 mm/ 6.29 in diameter, full width. Swept area of 194 cm sq | |
| Brakes, Rear | Drum brake 160 mm x 35 mm/ 6.29 in diameter, full width. Swept area of 194 cm sq | |
| Dimensions/Weights | ||
| Length x Width x Height | 2080 x 790 x 1010 mm | |
| Seat Height (Ballasted 75 Kg) |
785 mm | |
| Ground Clearance (Ballasted) | 170 mm | |
| Wheel Base | 1320 mm | |
| Weight - Ready for Road (Full Military Equipment) | 155 Kg | |
| Max Gross Weight | 375 Kg | |
| Weight Disribution (F/R) at Max Gross Weight | 150 / 225 Kg | |
| Fuel Consumption | 3.5 litres per 100 Km at 80 Kph | |
| Top Speed | 105 Kph | |