DKW RM 350

DKW
DKW RM 350, 1953 season
DKW RM 350
Manufacturer	Auto Union
Production period	1952 to 1956
class	Racing motorcycle
Motor data
Two-stroke, air-cooled three-cylinder engine
Displacement  (cm³)	348
Power  (kW / PS )	33 (45) at 13,000 rpm (1956)
Top speed (  km / h)	230 (1956)
transmission	4/5 speed gearbox
drive	Chain
Brakes	drum brake
Wheelbase  (mm)	1350
Empty weight  (kg)	approx. 160 (1956 with a small tank)

The DKW RM 350 was a racing motorcycle of the displacement class up to 350 cm³, which the Auto Union , Ingolstadt , built and used from 1952 to 1956 in the German championship as well as in the motorcycle world championship . Because of the screeching sound of its three-cylinder two-stroke engine , the machine was also known as the “ singing saw ”.

Engine and power transmission

Characteristic for the transversely installed three-cylinder engine of the DKW RM 350 were the cylinders arranged in a V shape, with the outer cylinders inclined by 15 ° and the middle one almost horizontal. The engine was cooled by the airstream. The longitudinal cooling fins of the central cylinder were unusual, in contrast to the usual transverse fins of the other two. The piston-controlled two-stroke engine had three carburettors, two with a common float chamber behind the upright cylinders and one above the cylinder. A six-cylinder magneto running at half engine speed from the BMW 328 (until 1953) or alternator and ignition distributor were mounted on the right of the engine, a multi-disc clutch running in an oil bath on the left of the gearbox that was interlocked with the engine. The sender for the electric rev counter was located on the left end of the crankshaft.

The engine of the first series designed by the former racing driver Erich Wolf (born 1912 in Wiesbaden and died there in 1970) developed 32  hp (23.5  kW ), but soon 38 hp (28 kW) at 12,000-12,500 rpm. Wolf's successor Helmut Görg (1911–1964) developed the unit further. Among other things, he replaced the cast iron piston rings with steel piston rings and enabled speeds in the range of 14,000 rpm and an output of initially around 40 hp (29.4 kW). In addition, the engine was switched from magnetic to battery ignition. At the end of the 1956 racing season, an output of 45 hp (33 kW) at 13,000 rpm and a maximum torque of around 30 Nm are said to have been achieved. The most favorable speed range was between 8800 and 9500 rpm; the maximum possible speed was given as 15,000 rpm.

The first exhaust system of the RM 350 developed by Wolf had an increasing cone or expansion cone behind each outlet slot of the three cylinders, behind it an intermediate piece and an opposite cone as a recoil cone and a thin tailpipe. Similar to the resonance exhausts used later in particular to optimize the performance of two-stroke engines, this design should generate a suction effect and accelerate the exhaust gas flow, while on the other hand, it should return any fresh gas that has escaped into the outlet.

The RM 350 initially had a four-speed, later a five-speed gearbox with a dog clutch that was connected to the crankshaft via gears. A rearward-facing, relatively small footshift lever and the open chain for transmitting power to the rear wheel were on the right-hand side.

• Engine of the DKW RM 350 from 1953
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Frame, landing gear and fairing

Like the smaller DKW racing motorcycles, the first version of the RM 350 had a double tubular frame , a telescopic fork at the front with hydraulic shock absorbers between the fork tubes and a rear swing arm with hydraulically damped spring struts, 19-inch wheels, light alloy rims and full-hub brakes operated by cables. The dry weight of the machine was 90 kg. In 1954 the RM 350 received a central tubular frame , the telescopic fork was replaced by a fork with a pushed short-arm swing arm and the handlebars were covered. In 1955 there were further improvements: The frame was reinforced, the tuning fork and rear swing arm were changed - a long rocker could optionally be used at the front - and the brake system was converted to hydraulics. The foot brake or the main brake cylinder acted on both wheels, while the front was also braked mechanically by hand. The front brake was now designed as a double duplex brake with four brake cylinders ; Brake drum diameter - different according to the sources - 200 mm or 250 mm. Large ventilation funnels were attached to the left and right of the fork to cool the brake. What was particularly new was the cladding with a “full-view pulpit” that reached from the front wheel to the center of the vehicle and far down. In addition, there was a separate rear panel with only one seat instead of the original double bench. Air ducts were let into the front fairing to cool the engine. The chassis changes and the fairing made the motorcycle considerably heavier, but enabled speeds of up to 230 km / h depending on the gear ratio and shape of the fairing.

The cladding shapes were developed on 1: 5 models in the wind tunnel of the Technical University of Munich, differently for high-speed and winding routes. The driver could hide himself completely behind the former, while the latter, with larger cutouts, left freedom of movement for arms and legs. The cladding was hand driven from sheet aluminum and weighed up to twelve kilograms. With the approval of the Bavarian State Ministry for Economics and Transport, Auto Union used the unlocked motorway (today's A9) between Auwaldsee and Manching for test drives; The only requirement was a red test drive license plate on the machines. The approval of July 12, 1954 stated, among other things: “On the basis of Section 70 of the Ordinance on the Admission of Persons and Vehicles to Road Traffic - Road Traffic Licensing Regulations  - in the version of August 24, 1953, the company Auto Union becomes always revocable for the DKW motorcycles with the chassis numbers 09081 to 09090 exempted from the regulations of § 49 StVZO on exhaust noise and driving noise. "

Racing successes

The DKW RM 350 made its debut after an unsuccessful start attempt in Hockenheim due to clutch damage in June 1952 at the Eilenriederennen in Hanover, which Ewald Kluge and Siegfried Wünsche finished in first and second place with the new machine. This followed a development period of nine months, with the first test runs of the new engine in a 250cc chassis in the spring of 1952. 1955 was August Hobl on DKW RM350 third in the 350 cc World Championship and German champion and 1956 runner-up and again German master class to 350 cc. In 1953, Siegfried Wünsche won the 350cc class of the Eifel race at the Nürburgring , in which his initially leading colleague Kluge fell badly due to a broken fork and ended his career. In spite of the rain, Wünsche drove the six laps on the 22.81 km long Nordschleife in 1: 18: 02.6 hours or at an average speed of 105.22 km / h. In 1954 the DKW drivers Karl Hofmann , August Hobl and Karl Bodmer achieved a triple victory at the Nürburgring and the Eifel races in 1955 and 1956 also won DKW drivers in the class up to 350 cm³. Hofmann was fastest over six laps in 1: 07: 40.6 hours.

Technical specifications

Parameter	DKW RM 350 at the end of the 1956 racing season
engine	V3 cylinder two-stroke, cylinder angle 75 °
Displacement	348 cc
Bore × stroke	53 mm x 52.8 mm
compression	1: 10-1: 14.1
power	approx. 45 hp (33 kW) 13,000 rpm
Carburetor	3 Dell'Orto S5 / 28 mm Ø with gauze filter, air to be regulated from the handlebar with three levers
alternator	6 V 4.5 A
transmission	5-speed claw gear with foot shift , primary drive via gear wheels ( Getrag gear wheels ), rear-wheel drive via roller chain
frame	Central tubular frame made of tubular steel fork with pushed swing arm, springs with shock absorbers in the fork tube, spring travel 50 mm, rear swing arm with Girling struts, spring travel 58 mm
Brakes	Full-hub drum brakes, Ø 200 mm (front double duplex ), brake shoe width 25 mm, front and rear hydraulically operated with a foot lever, in front also mechanically
wheelbase	1350 mm
tank	11–32 l depending on the route
consumption	8–11 l / 100 km, depending on route and weather
Dry weight	147 kg
Top speed	225–230 km / h (stopped on the highway)

literature

• Reiner Scharfenberg: DKW RM 350 - the "singing saw" . Motorcycle Profile No. 3, Unitec Medienvertrieb, Königsmoos 2009.

Individual evidence

1. ^ ^{A b} Siegfried Rauch: DKW - The story of a global brand . Motorbuch Verlag, Stuttgart 1988, ISBN 3-87943-759-9 , pp. 220-223.
2. ↑ ^{a b c} K.-H. Edler, W. Roediger: The German racing vehicles . Fachbuchverlag Leipzig, 1956. Reprint, ISBN 3-343-00435-9 , pp. 213-216.
3. ↑ ^{a b c d e f g} Reiner Scharfenberg: DKW RM 350 - the "Singing Saw" . Motorcycle Profile No. 3, Unitec Medienvertrieb, Königsmoos 2009.
4. ↑ ^{a b} Zweiakte.de. DKW 1956 . Retrieved March 22, 2016.
5. ↑ Pavel Husàk: Two-stroke motorcycles . 1st edition. Motorbuch Verlag, Stuttgart 1980, ISBN 3-87943-634-7 , pp. 193-195.
6. ^ DKW in motorsport . Retrieved March 23, 2016.
7. ↑ Michael Behrndt, Jörg-Thomas Födisch, Matthias Behrndt: ADAC Eifelrennen . Heel Verlag, Königswinter 2009, ISBN 978-3-86852-070-5 .