Brake Horse Power
Cylinder TUM 80

Torque
Cylinder TUM 80

Maximum Speed

18.7 MPH (30.1 kph) at 4000 RPM

Maximum RPM

4000 RPM

Climbing Ability

1 : 12.5 (8%) hill without pedalling

Brake Mean
Effective Pressure

BMEP = (600,000 x Max Power kW) / (Swept cc x Maximum Power RPM)
2.84 bars at 2500 RPM

Sound Level

Early S 3800

Later S 3800

65 dBA at 1875 RPM

77 dBA at 1875 RPM

Fuel Economy
Cylinder TUM 80

Fuel Octane

Regular Unleaded Fuel (ie: UK 95 RON, US Pump 89 AKI)

Pre-Mix Oil

Castrol Super TT 2-Stroke Mineral Oil at 50 : 1 to 33 : 1 (2 - 3%)
Castrol Scoot-R Semi-Synthetic 2-Stroke Oil at 50 : 1 (2%)
16.6 : 1 (6%) for first 50 miles (80 km)
33 : 1 (3%) for next 250 miles (400 km)

Fuel Tank

1.25 litre nominal

1.4 litre maximum

Fuel Cap

25 ml [cc, cm³]

35 mm Camera-Film Container

Fuel Range

47 miles (75 km) nominal at 4000 RPM

53 miles (85 km) maximum at 4000 RPM

Carburettor

Gurtner 6,5 LI

Jet

Hole Diameter

Venturi

-

6.5 mm

Main Jet

28 cc[cm³] / minute

0.480 mm

29 cc[cm³] / minute

0.488 mm

30 cc[cm³] / minute

0.497mm

31 cc[cm³] / minute

0.505 mm

32 cc[cm³] / minute

0.513 mm

Enrichment Jet

551 cc[cm³] / minute

1.96 mm

Dispersion Jet

221 cc[cm³] / minute

1.24 mm

Air Filter Holes

2 x 5.7 mm internal diameter (designed to reduce induction noise)

Cylinder

Engine N° 3.800.000 onwards

TUM 80

Engine N° 4.200.000 onwards

TUM 80A

TUM 80A CM 6,5

TUM M 80A CM 6,5

Cubic Capacity

49 cc [cm³]

Bore

39.5 mm

Stroke

40 mm

Swept Volume

37.01 cc [cm³]

Con-Rod

Length

90 mm

Small-End Width

12.25 mm

Small-End Clearance
(side-to-side)

3.75 mm

Crank Pin Offset

20 mm

Decompression
Valve

Fully tighten Decompression Valve nut, then unscrew 1½ turns

Crankcase
Compression Ratio

1.45 : 1

Crankshaft Bearing
(Magneto end)

Type

6202-2RS (RS = 1 seal, 2RS = 2 seals)

Outer Diameter

35 mm

Inner Diameter

15 mm

Width

11 mm

Crankshaft Bearing
(Flywheel end)

Type

6203-2RS (RS = 1 seal, 2RS = 2 seals)

Outer Diameter

40 mm

Inner Diameter

17 mm

Width

12 mm

Crankshaft
SPI Lip Seal
(Flywheel end)

Type

Early Type (Up to March 1970)

Outer Diameter

40 mm

Inner Diameter

21 mm

Width

3.5 / 4.5 mm

Type

Later Type (April 1970 onwards)

Outer Diameter

31 mm

Inner Diameter

21 mm

Width

3.5 / 4.5 mm

Piston

Cylinder Type

TUM 80,  TUM 80A,  TUM 80A CM 6,5

TUM M 80A CM 6,5

Height (along edge)

49.45 mm

46.98 mm

Height (crown-to-skirt)

53.30 mm

50.83 mm

Crown Height

3.85 mm

Width

39.35 mm

Groove Vertical Height

1.70 mm

Ring Vertical Height

1.67 mm

Ring Horizontal Width

1.60 mm

Ring Side Clearance

0.01 mm (0.03 mm typical, 0.04 mm maximum)

Ring Gap

Gap = 0.5% x Bore (ring inserted 5 mm from top of cylinder)
0.15 mm (0.2 mm typical, 0.7 mm maximum)

Skirt Thickness

1.30 mm

Clearance (skirt-to-cylinder)

0.08 mm - 0.12 mm (measured around skirt)

Gudgeon Pin

30.5 mm length x 12 mm diameter

Maximum Piston Speed

Maximum Piston Speed = 2 * Stroke * Maximum RPM
5.33 m/sec (17.5 ft/sec or 1050 ft/min) at 4000 RPM

Cylinder Head

Volume

Total Unswept Volume
6.81 cc [cm³]

Gasket Thickness

Gasket compressed
0.8 mm

Squish Step

1.5 mm depth x 43 mm diameter

Combustion Hemisphere

15.5 mm depth x 32 mm diameter

Cylinder Liner

Length

87.7 mm

Top Edge

Liner Top Edge above Cylinder Top Edge
1.5 mm

Deck Height

Liner Top Edge above Piston Top Edge at TDC
0.8 mm

Geometric
Compression Ratio

8.2 : 1

True
Compression Ratio

Also known as Swept or Trapped Compression Ratio
6.44 : 1

Cranking
Compression
Pressure

CCP = True Compression Ratio x 1.013185
6.63 bars (663 kPa or 96.11 PSI)

Peak
Combustion
Pressure

PCP typically equals Cranking Compression Pressure x 5.5
36.44 bars (3644 kPa or 528.58 PSI)

Clutch

Automatic

Roller

42 mm diameter Carborundum Roller on Front Tyre

Slippage

5% nominal

Generator Coil
Before 1976

6V AC (10VA)

Stoplight Coil
4600 V2-V3 US

6V AC

Additional 6V Coil

Generator Coil
From 1976

Motobecane

6V AC (17VA - 25VA)

Wire Gauge

26 SWG

Wire Length

9.29 m

Wire Diameter

0.454 mm

Number of Layers

2

Length Of Layer

45 mm

Turns Per Layer

99

1st Turn Length

46 mm

Number Of Turns

225

Resistance

0.96 ohms

Inductance

4.14 mH

TopSPICE Model

.MODEL IRONCORE CORE (AREA=0.88 PATH=5.1 MS=6E5)

Generator
Output

RPM

VRMS AC (no load)

500

3.5

2500

17.7

4000

28.3

6000

42.4

Front Bulb

Before 1976
10VA Coil

6V 6W (1A), E10 Screw Base or EP10, Yellow Glass

From 1976
17-25VA Motobecane Coil

6V 15W (2.5A), P26S base, Yellow / Clear Glass

Rear Bulb

Before 1976
10VA Coil

6V 4W, E10 Screw Base, Clear Glass

14V AR 7W (0.5A), E10 Screw Base, Clear Glass

12V 6W (0.5A), E10 Screw Base, Clear Glass

From 1976
17-25VA Motobecane Coil

6V 2W, Bayonet Base, Clear Glass

6V 4W, Bayonet Base, Clear Glass

12V 6W (0.5A), Bayonet Base, Clear Glass

12V 4W, Bayonet Base, Clear Glass

6V 10W [UK], BA15S Bayonet Base, Clear Glass

Electric Horn (UK)

12V AC

From extra 6V coil in series with 6V Lighting Coil

Electric Horn (US)

6V AC

Powered by 6V Lighting Coil

Magneto

F.A.GY. HUNGARY, MARCALI, C2000

LT Primary Winding

HT Secondary Winding

Wire Gauge

26 SWG

48 SWG

Wire Length

10.68 m

775.31 m

Wire Diameter

0.454 mm

0.057 mm

Number of Layers

2.5

19.5

Length Of Layer

40.9 mm

40.9 mm

Turns Per Layer

90

718

1st Turn Length

46 mm

53.27 mm

Number Of Turns

225

14000

Resistance

1.1 - 1.2 ohms

4.5K - 4.75K ohms

Inductance

4.7 - 5 mH

15 - 17 H

Turns Ratio

62.2 : 1

TopSPICE Model

.MODEL IRONCORE CORE (AREA=0.88 PATH=5.1 MS=6E5)

Contact Breaker 

Gap

0.4 mm (0.015")

Dwell Angle

Breaker Closed Angle[°]
260° (65° out of 90°) (72.5%)

Condenser

0.2uF 500V DC nominal (0.18uF - 0.25uF)

Timing

23.5° BTDC (2 mm BTDC)

Spark Plug

Original Fitting

Bosch W7AC
Champion L86C
Cyklon 43
Flashpoint FP 5CR
NGK B6HS
Marchal V36A

Original Fitting
Projected-Nose

Bosch W7BC
Champion L86YC
NGK BP6HS

Warmer

Bosch W8AC
Champion L92C
NGK B5HS

Warmer
Projected-Nose

Bosch W8BC
Champion L92YC
NGK BP(R)5HS

Hot

Bosch W10AC
Champion L95C
NGK B4HS

Hot
Projected-Nose

Bosch W10BC
Champion L95YC
NGK BP(R)4HS

PLUG GAP

0.5 mm (0.020")