BMW R 25/3
| BMW | |
|---|---|
 |
|
| R 25/3 | |
| Manufacturer: | BMW |
| Construction time: | 1953-1956 |
| Number of pieces: | 47,700 |
| Previous model: | R 25/2 |
| Successor: | R 26 |
| Technical specifications | |
| Engine : | Single cylinder four-stroke engine |
| Displacement : | 247 cc |
| Performance : | 13 hp (9.6 kW ) at 5800 min -1 |
| Gearbox : | Four-speed foot-operated gearbox |
| Drive : | Cardan |
| Empty weight : | 150 kg |
| Top speed : | 119 km / h |
| Tank capacity : | 12 l |
| Fuel consumption : | 2.9 l / 100 km |
The BMW R 25/3 was a motorcycle by the German manufacturer BMW that was built from 1953. It was the successor to the R 25/2 .
history
The engine of the R 25/3 developed 13 hp (9.6 kW). It had a long-stroke, hydraulically damped telescopic fork and was the first BMW motorcycle to be mass-produced with full-hub brakes. At the rear, the straight- path suspension was retained, in contrast to the swing arms of the later models, which appeared from 1955. The previous model, the BMW R 25/2 , had a nominal output of 12 hp (8.8 kW).
The R 25/3 was replaced in January 1956 by the BMW R 26 model with a more powerful engine (15 HP / 11 kW) and a completely new chassis with a full swing frame , the basic concept of the drive remained the same.
technology
The closed double tube frame, welded from tubular steel, carries four spherical heads on the right for the connection of a sidecar . The Steib LS 200 was a suitable sidecar, but it required a special gear ratio for the cardan drive and an exchange of the speedometer. (The speedometer cable is driven by the gearbox output shaft, not by an impeller.) The front mudguard has the curved dirt flap incorporated into the sheet steel, which is missing in the successor models. Compared to the R 25/2, the tank has been enlarged and the lockable tool compartment has been moved from the top of the tank to the left.
The cast aluminum gearbox and engine block are mounted in the frame with quick-release axles, with rubber bushings designed to reduce the transmission of vibrations. The torpedo-shaped muffler of the exhaust is also attached directly to the frame with rubber bearings. The rear axle drive housing is also made of cast aluminum.
engine
Like the previous model, the BMW R 25/2, the BMW R 25/3 is powered by a longitudinally installed single-cylinder four-stroke engine. The multi-part, pressed crankshaft has three roller bearings in the engine housing, the non-divisible connecting rod has roller bearings on the crank pin. A side camshaft controls the valves via tappets , push rods and rocker arms . The externally chrome-plated tappet guides are screwed into the engine block on the left and the chrome-plated steel bumper protection tubes are pressed into the gray cast iron cylinder on the left. The protective tubes are sealed against the slide guides with rubber elements. The push rods actuate the valves hanging in a V-shape in the aluminum cylinder head via rocker arms, which, like the piston pin, are mounted in bronze bushes. The combustion chamber is hemispherical. The camshaft is driven by the crankshaft via a simplex chain . The gear oil pump sits in the oil pan and is driven by the camshaft via a drive shaft with worm drive ( reduction ). A sieve plate is attached in front of the oil suction bell; there is no oil filter. A riser, which is pressed in on the right side of the cylinder, supplies the valve control with oil. The oil flowing back from there reaches the camshaft via the protective tubes and the tappets. The oil slinger on the crankshaft distributes the oil in the crankcase. The motor housing is vented via a rotary vent valve with a bent pipe that ends on the left side of the oil pan outdoors. After thermal problems with the previous models, the R 25/3 was given a cylinder head painted matt black and valve covers painted matt black. The black cylinder head was popularly known as the “Mohrenkopf”.
The generator of the 6 V 60 W direct current ignition alternator of the Noris ZLZ 60/6 / 1600L type with centrifugal ignition adjuster sits behind a sheet steel cover, encapsulated in a splash-proof manner on the front crankshaft stub . The charge regulator for the lead accumulator (battery) has an inclined characteristic curve and, as was common in motorcycle construction at the time for reasons of price, space and weight, is a so-called regulator switch, i.e. a combination of current and voltage regulator with reverse current switch. Like the ignition interrupter, the capacitor and the ignition coil, this is located under the sheet steel cover.
On the rear crankshaft stub is the heavy flywheel (with the ignition timing mark in the form of two nickel-plated steel balls that can be seen in the inspection hole), which accommodates the single- disk dry clutch . The clutch is operated via a thrust bearing and a push rod running through the hollow main shaft of the gear unit.
The carburetor is a 24 mm Bing float chamber carburetor (model: 1/24/41 or -42) with a conical partial load needle in the round slide. The float chamber is on the left side of the mixing chamber, which is why the carburettor has a compensation chamber on the right for safe sidecar operation. Its idle system is adjustable with an idle nozzle and an idle air screw, a swab is used to enrich the cold start mixture, and the intake air on the air filter can also be throttled with a rotatable rosette. Alternatively, a SAWE carburetor (model: K 24 F) was installed at the factory, less often than the Bing carburetor. The wet air filter element is formed by an oil-wetted steel mesh, it is located at the end of a pipe that runs through the tank parallel to the bottom of the tank and ends near the telescopic fork. The connection of this long suction pipe between the tank and the carburetor is made by a rubber socket. The air filter is cleaned for maintenance and re-wetted with oil. The long intake path should ensure a good torque curve in the lower speed range and was responsible for the characteristic rattling intake noise of the R 25/3.
drive
The claw-shift four-speed transmission has a torsion damper and an elastic torque transmission element at the transmission output. For this purpose, a black rubber four-hole disk (Hardy disk ) is pushed onto the two- finger flange of the gearbox, which transfers the torque from the gearbox output shaft to the two- finger mount on the drive shaft. For reasons of stability, this hard disk is equipped with a chrome-plated steel ring. On the successor models R 26 and R 27, this is painted because it rotates under a cover shell.
The cardan shaft to the rear wheel is free-running and has a high-gloss chrome-plated finish. The universal joint of the drive shaft, which is attached to the angular gear and can be lubricated with a grease nipple, is covered against dust with an aluminum screw cap, the so-called cardan bell. A rubber dust cap that rotates with the shaft runs against this bell and keeps loose dirt away from the universal joint. The angular gear in the cast aluminum body has the smooth running due to spiral-toothed bevel gears (90 ° deflection).
Wheels and brakes
The R 25/3 had light alloy full-hub brakes and 18 "light alloy rims. The previous model R 25/2 had steel rims and steel half-hub brakes (“ can end brakes ”) with a smaller braking surface and effect. The wheels have straight spokes, what The risk of broken spokes is minimized with the heavy loads in sidecar operation.Both wheel hubs are provided with drive teeth so that the wheels can be interchanged with the same tire size.
Technical specifications
| Parameters | BMW R 25/3 |
|---|---|
| number of items produced | 47,700 |
| drilling | 68 mm |
| Hub | 68 mm |
| Compression ratio | 7: 1 |
| Power transmission | Four-speed manual gearbox, Hardy disc and open cardan shaft to the rear wheel |
| Consumption approx. (L / 100 km) | approx. 3 |
| total weight | 320 kg / 450 kg with sidecar |
| Tank capacity | 12 liters |
| wheel size | 3.25-18 |
Web links
- BMW R 25/3. In: BMW history. BMW AG(dossier of the BMW Group archive).
- Motorcycle manual R 25/3. (PDF) In: BMW history. BMW AG, October 1953(manual with pictures, 85 pages).
- BMW single cylinder information center. a private, non-commercial fansite(many manuals and spare parts lists).
Individual evidence
- ↑ Steib LS 200 . meisterdinger.de. Retrieved January 15, 2019.
