Junak Motorcycles

Today in Motorcycle History

Junak M10 1958 Model

The following is from two sources, apologies for duplication.

General Description

Has no lug for the chain cover; on the seat, armband passenger handle; decorative grille under the headlight is rectangular. Mudguards are deeply valanced, full-width cast iron brake drums, and built-in lamp. Fairly small carburettor.

Colour: all white (or perhaps cream or light yellow). White frame, white seat, polished drums, chromed rims and spokes.

So there were several paint schemes. Sequentially: cherry red, black, cream mudguards and tank; the rest is black. Then came an all-white (or cream or yellow) version.

A relatively long period elapsed between the development of the Junak's construction to the launch of serial production, and then began the modernization process of the motorcycle. The changes concerned mainly the engine and chassis, among them an increase in compression ratio and the use of a new Polish-made carburettor.

In the same year, a new designation for the Junak M10 motorcycle was introduced. The SO3 engine underwent several significant changes - the compression ratio was raised from 6.8 to 7.0. the power increased, becoming 12.5 kW (17 km) 6000 rpm, and the torque increased to 27.5 Nm (28 kgm) at 3800 rpm. A Polish horizontal carburetor was used, Pegaz g26 ul type, with a throat diameter of 26 mm and a starting device. The electrical installation has also changed and the motorcycle received a brake light. Spark plug became ml4x l.25 thread, 175 calorific value (according to Bosch).

Sound signal sp56 located in the housing of the reflector. In the drivetrain it got a new clutch and a full chain guard. Front wheel travel increased to 150 mm, rear wheel travel to 100 mm. The brakes are mechanically actuated, independent front and rear drum brakes, with full-width hubs. Light alloy cast brake drums with cast iron insert. Internal diameter of brake drums 200 mm, brake lining width 40 mm. Hand brake and foot brake controlled by Bowden cables.

Speedometer drive with a flexible shaft from the rear wheel. Steel tube handlebars attached to the top of the fork, and moved forward compared to the m07 model. The handles of the clutch and handbrake levers are integral with the handlebars, the decompression lever and the light switch with the signal button are mounted on the left side, the air throttle (choke) lever is on the right side.

Deeply valanced mudguards, pressed from steel sheet. Front mudguard attached to the moving part of the fork. Luggage rack of pressed metal attached to the fuel tank. Three-position fuel tap. Dual seat with cushion made of porous rubber, cover made of dermatoid, top and sides made of leather. Battery compartment in the rear part of the frame, air filter on its left side, tool compartment on the right. Adjustable rider's footpegs with rubber covers, and folding passenger footpegs with rubber covers.

Central base, welded, made of steel pipes, suspended on the lower beams of the frame. Side stand on the left, non-dismountable exhaust muffler on the right side of the motorcycle - for now as in the M07 model, but later two more types of long mufflers will be developed.

Wheelbase 1417 mm, total length 2200 mm, width 735 mm, height 1045 mm. Front seat height 790 mm, rear seat height 855 mm. Distance between the saddle surface and the rider's footrests 560 mm. The lowest point from the road (central stand) 115 mm. Weight - 193 kg. Permissible load 160 kg., permissible total weight 355 kg., permissible load on the front wheel 125 kg, rear wheel 230 kg. capacity fuel tank 17 litres, engine lubrication system 2.4 litres, clutch chamber 0.5 litres, gearbox 0.4 litres.

Operational data: maximum speed 125 km/h. Fuel consumption 3.5-4.2 litres/100 km. 400m standing start 21.7 seconds.

Air pressure in tyres: front 0.14 MPa (1, 4kg/cm2), rear 0.16MPa (1.6kg/cm2).

M10 models were subject to changes during production, so this description may not fully co-incide with the models owned by users.

Other changes occurred during production, including an increase in compression ratio and the use of a new Polish-made carburettor.


General information
Mark SFM Szczecin
Type M10 "Junak"
Total length 2172mm
Width 740mm
Height (unloaded) 1095mm
Wheelbase 1417mm
Rider's seat height 755mm
Cross clearance 170mm
Front wheel overtake 72mm
Weight, equipped, without fuel 170 kg
Weight limit 200 kg
Maximum speed 125 km/h
Fuel consumption at 60 km/h 3.5L/100km

The engine and chassis numbers are listed on the nameplate located on the left side of the head tube. In addition, the engine number is stamped on the left engine housing, at the base of the cylinder. The chassis has a number stamped on the right side of the head tube.

Technical description


Type :
S03 - four-stroke, carbureted
Type :
single-cylinder, overhead valve, air-cooled
Cylinder Diameter:
Piston stroke:
Displacement :
349 cm 3
Compression ratio:
Rated power at 6000 rpm :
19 hp (14 kW)
Capacitive Power Index :
54 HP/L (39.7 kW/L)
Maximum torque at 3800 rpm :
2.8 kg/m
Dry engine weight:
63 kg
engine block:
vertically split crankcase and gearbox in a common light alloy cast housing
Cylinder :
cast iron
head :
aluminum alloy with pressed seats and valve guides
Piston :
with convex bottom, made of aluminum alloy Floating piston pin
Rings :
2 sealing and 1 scraper (upper chrome sealing)
connecting rod:
forged alloy steel; plain bearing in the connecting rod head, roller bearing in the foot
Crankshaft :
folding; forged carbon steel counterweights, alloy trunnions
Main bearings :
3 x roller
valves :
upper; controlled by cams via pushrods and rockers; clearance adjustment with eccentric shafts that simultaneously secure the rocker arms in the head
Valve clearances :
measured with a warm engine
Lubrication :
circulating under pressure
Oil pump :
toothed, double driven from the crankshaft; oil tank located in the hull, around the gearbox chamber
Oil filter :
placed in the oil tank
type G26, throat diameter 26 mm
Air filter :
wet with metal mesh filter cartridge
foot operated by means of a lever with a ratchet
Transmission engine - clutch:
roller chain, double row 3/8"; gear ratio 23:56
Clutch :
4-disc, wet, cork, with a central spring
4-speed constant-mesh gear; ratio sizes:
  • 1st run 3.04
  • 2nd gear 1.97
  • 3rd run 1.296
  • 4th run 1.00
gear change :
foot lever, on the left; the automatic mechanism of the mechanism allows you to engage only one gear by pressing the lever fully


frame :
cradle, double, welded from steel pipes with an elliptical cross-section, non-dismountable
Front suspension :
telescopic, classic, with oil damping; stroke 146 mm
Rear suspension:
telescopic, on a swingarm with oil damping; swing arm welded from steel tubes, equipped with two-way chain tensioners
front and rear with aluminum alloy center hubs; ball hub bearings ; thru axles
Rear wheel drive:
roller chain, single row 5/8" with 102 links, gear ratio gearbox - rear wheel 1: 2.4
Brakes :
maxillary; front manual, rear foot
Steering wheel :
tube for position adjustment
Fuel tank :
pressed from steel sheet, covered inside with a protective coating, connected to the carburetor with a needle-like pipe
Muffler :
non-dismountable, pressed from sheet metal, placed on the right side of the motorcycle
Saddle :
double, covered with leather and leather, filled with latex sponge
Trunk :
pressed from sheet steel, bolted to the fuel tank

Junak M10 Parts Catalogue

Part No
part name
  Complete engine
  head and cylinder
  Crank system
  Timing and drives
  Oil pump
  Gear changer
  Electric drives
  Engine electrical installation
  Front fork
  Chain guard
  Fuel tank
  Driver footrest
  Exhaust pipe and muffler
  Air filter and tool box
  Front fender
  Rear brake pedal
  Rear mudguard
  Steering wheel
  Central stand
  Rear shock absorber
  Passenger footpegs
  side stand
  Rear wheel
  Front wheel
  Chassis electrical system
  Headlight cover

Polish History Archive
Junak.net Archive