The invasion of Crete revealed for the first time the use by the Germans of the motorcycle
tractor for the purpose of hauling light, single-axle, open trailers or light guns. This
tractor is known to be employed in the Middle East and, according to recent newspaper
accounts, it is now to be seen on the Eastern Front. It is a suitable vehicle for accompanying
airborne troops. Early in 1941, it was accepted as an army vehicle and received the
number Sd.Kfz. 2 (Sonder Kraftfahrzug--special motor vehicle).
The accompanying sketches show that the body (1) is a box-like structure made of pressed metal
in two halves, and joined along a horizontal plane below the track-guards (2). It contains
the driving position (3), the engine (4) and transmission, and a transverse seat (5) at
the rear over the cooling system (6). The driver is seated on a saddle (7) mounted above
the gearbox (8) and clutch housing (9), and has two rubber knee-pads fitted beneath the
dashboard. On each side, the track-guards carry gasoline tanks (10) at the front while, level
with the engine, the sides are built up (11) and contain on the left the tool kit and
on the right the battery and fuze panel.
At each side of the passenger seat there is a light rail (12), while foot rests, rifle
rests (14), and clips (15) are provided at the rear.
The power unit (4) is an Opel "Olympia model 38," gasoline engine, mounted towards
the rear of the body. It is a four-cycle, four-cylinder unit developing about 36 brake
horse power at 3,400 rpm.
|Bore|| ||80 mm|
|Engine capacity||1,478 cc|
|Firing order||1 - 3 - 4 - 2|
The engine body is in two main parts: the cylinder head, and the cylinder block and
crankcase (both in one piece).
c. Crankshaft Assembly
This is supported in four main bearings. The pistons are of light metal and are fitted
with two compression and one oil-scraper rings. The wrist or piston pins are full
floating and are prevented from sideward movement by locking rings on each side.
d. Valve Operation
The overhead valves (one intake and one exhaust for each cylinder) are operated by
pushrods and rockers from the camshaft, which is mounted in four bearings in the
crankcase. The gasoline pump, tachometer, oil pump, and distributor are all driven
from the camshaft.
|Valve clearance (warm)|| ||Intake|| ||0.2 mm (8/1000 in)|
| " "||Exhaust|| 0.3 mm (12/1000 in)|
An impeller-type water pump, together with the generator, is driven from a master
pulley on the free end of the crankshaft and circulates water between the engine
and the radiator (6), which is located at the rear of the vehicle. A small water
tank is mounted above the pump.
The laminated radiator is built in a large airduct (16), in which there is a
fan (17) driven direct from the crankshaft. The rear end of the airduct may be
closed by a flap (18) operated by a hand lever on the left of the driver.
Oil is pressure-circulated by a gear pump from the sump through a strainer and
passes through the bearings of the crankshaft, connecting rods, camshaft, tappets, and
valve rockers at a pressure of 30 to 45 pounds per square inch. Piston pins and
cylinder walls are splash-lubricated.
In order that the oil pressure may not rise too high, there is an excess-pressure
valve in the wall of the oil pump, and this returns some of the oil to the sump.
An oil cleaner of the metal-disk type is fitted. This is itself cleaned by
turning the ratchet on the top.
An Opel downdraft carburetor, with a large oil-bath-type air filter (19) on the
air intake, is fitted. Gas is drawn from the tanks (of which there are two, each
holding 5.5 U.S. gallons) and fed to the carburetor by a mechanical diaphragm
pump of normal design, which is driven from the camshaft.
h. Electrical Equipment
Ignition is by Bosch coil and distributor, the latter being driven from the
camshaft. A Bosch 75-watt generator, with voltage regulator, is
mounted on the right side of the engine and together with the water pump is
driven by a V-belt from the master pulley. A Bosch starter motor is
also fitted on the right side. The 6-volt battery is mounted on the
right side above the track-guard.
i. Starting Equipment
Normally the engine is started by a self-starter controlled by a pull-knob on the
dashboard. A crank is also provided and, for use, is inserted in an opening in the
radiator grill at the back of the vehicle (just above the trailer coupling) and
pushed through to engage with the crankshaft.
Transmission is through an Opel multiple-spring, single dry-plate clutch, mounted on
the flywheel, to a 3-speed-and-reverse gearbox (8), which also incorporates an
auxiliary gear box, giving high and low ratios so that in effect 6 forward speeds
may be obtained. A long gear-shift lever (20), held near the top in a
gate (the H-shaped aperture in which the gear lever operates) on the
dashboard in front of the driver, gives the main gear selection, while a
shorter lever (21), to the rear of the first, gives selection of high and low ratios
for road or cross-country travel. A hinged latch which covers the "reverse" part
of the gate prevents accidental engaging of that gear, while an extension of the
latch beyond the hinge makes its removal an easy matter.
The vehicle must be stationary while changing ratio in the auxiliary gearbox.
The speedometer is driven from the gearbox.
The differential (22) is of the controlled spur-gear type and incorporates two
steering brakes (23), one for each track. These are internal expanding, and in
order to increase their braking efficiency the drums are not directly fastened
to the axle shafts, but are driven at considerably greater speed from the
differential spur pinions through a set of gears.
From the differential, the drive passes through the steering brakes (23) and
metal couplings (24) to the final reduction gears (25), and thence to the
sprockets (26). Each sprocket is a narrow twin-rimmed wheel, of which the
inner and outer rims are shod with rubber pads (27) (12 per rim) to form a
continuous tire. The pads have the same inside curvature as the rim, but are
flat outside. Adjustable rollers (28) (12 per sprocket) are fitted between the
rims to act as teeth and to engage the track. An internal expanding brake, which
is foot operated, is mounted inside each sprocket.
(1) Front Wheel
The front wheel (29) is a pressed-steel disk type with
a 3.5- by 19-inch tire (tire pressure 34 lbs. per sq. in.) and
mounted in a pressed steel, motorcycle front-wheel fork (30) of conventional
pattern. The springing (two vertical coil springs) (31), with controllable
friction-disk shock absorbers (32), and the steering column (33) are very
similar to those of a normal motorcycle.
(2) Track Assembly
The track assembly, which is of the usual type for half-track vehicles, consists on
each side of a driving sprocket (26), four equal size, double-rimmed bogie wheels (34
and 35), and an idler wheel (36). Of the bogie wheels, the odd numbers (34) (from
the front) are narrow wheels with radial spokes, while the even numbers are wider,
pressed-steel disk wheels. The former run between the rims of the latter, the whole
bogie and idler system being set rim to axle.
The bogie wheels are mounted on bell cranks (37) fastened to torsion bars, which
pass across the body of the vehicle in crosstubes (33) of circular section and are
anchored in the opposite side. The torsion bars of the corresponding bogie wheels of
the two sides are carried one above the other (39) in the same cross tube.
The idler is simply another narrow-rimmed bogie wheel and is carried on an eccentric
arm (40) which can be adjusted by a screw rod (41) passing through a bracket on the
body. By this means the position of the idler can be varied, and hence the track
tension may be adjusted. The bogie and idler wheel rims have thin, solid rubber tires. There
are no return rollers, the track returning along the tops of the bogie wheels.
Each track is made up of 40 forged steel links (42) (fig. 1) joined together
by a bolt (43). These link joints are lubricated from oil chambers (44) which
also, in part, form the tongues of the track links and pass between the rims of
the bogie wheels. Above the oil chambers and track bolts, rubber shoes (45) are
mounted. These are easily replaceable, being retained by 4 screws (46) only.
The motorcycle tractor is steered by the front wheel, by handlebars (47) in the
normal manner of a motorcycle, and for sharp turns, by the steering brakes, operating
on the tracks.
Two take-off rings (48) at the bottom of the steering column are connected by rods to
arms on the brake crosstube (49). These in turn actuate levers, the ends of which are
joined by means of adjustable rods to the steering brakes (23).
The steering brakes come into play for turns of over 5°, corresponding to a
movement in either direction of about 1 3/4 inches at the ends of the
The footbrake, which is located on the right, and the handbrake (50) both operate an
internal expanding brake mounted in each sprocket.
q. Driver's Controls and Instruments
These consist of the following:-
(1) steering handlebars with right hand throttle twist grip;
(2) main and auxiliary gear selection levers;
(3) a footpedal (51) on the left, operating the clutch;
(4) a handbrake (50) mounted on the left of the gearbox cover;
(5) a footbrake on the right;
(6) a radiator shutter control on the inside of the body, left of the driver, -
together with starter button, ignition and lighting switches, tachometer,
speedometer, odometer, oil-pressure gauge, and water-temperature gauge.
r. Modifications for Tropical Use
A German document details several modifications which are made to
the motorcycle tractor to fit it for use under tropical conditions.
The oil filler cap has a linen hood tied over it, and the breather pipe has
a steel-wool filter held between two pins near the bottom. For cleaning
purposes, the filter may be removed after the lower pin has been extracted.
In order to provide sufficient cooling, the fan is driven at 1.4 times
the crankshaft speed.
(3) Fuel Supply
The Opel carburetor is replaced by a Solex model, believed to be of the
duplex downdraft type. A filter is incorporated between the gas tanks and
(4) Air Filter
The "Knecht Tornado" air filter fitted to the normal vehicle is replaced by a
similar type of oilbath filter, incorporating a mechanical precipitator
on the inlet side.
(5) Electrical Equipment
A new generator is fitted, while a solenoid-operated starter motor replaces the
mechanically-operated type fitted in the normal model. The starter push button is
located on the right side of the body level with the driver's seat. The
distributor is enveloped in a linen bag.
Both main and auxiliary gear levers have linen hoods tied to them to cover their
points of entry into the gearboxes. The breather holes in the gearboxes, the
steering brakes, and the stub axle housings are all covered with cloth hoods.
For special purposes, tracks in which the links have extension plates (52) welded
to their outside (figs. 2 & 3) are provided. These are probably for use in
very loose sand or swampy ground.
The covers of the track brakes have extension plates welded to the upper halves
to prevent the entry of sand as much as possible.
The throttle twist grip is covered with a linen sheath which is tied to the grip at
each end and to the handlebars, with sufficient free cloth allowed between these
fastenings to permit full movement of the twist grip.
(10) Additional Equipment
A 0.4-gallon container for distilled water, and a gallon tank for radiator water
A length of wire (16 to 20 feet) and a 13- by 16-foot tarpaulin
complete the special tropical equipment of the motorcycle tractor.
s. Further Particulars
| ||Length, over-all|| ||9 ft|| || 0 in|
|Width, over-all||3 ft|| 3 in|
|Height, over-all||3 ft||11 in|
|Width between tracks||2 ft|| 8 in |
|Wheelbase, from center of front wheel to center of track||4 ft|| 5 in |
|Length of track in contact with ground||2 ft|| 8 in|
|Belly clearance|| || 9 in|
| ||Without load|| ||2,690 lbs|
|Axle load, front wheel|| 120 lbs|
|Load on tracks||3,248 lbs|
| ||Maximum speed on roads,|
| At 3,000 rpm|| ||38 mph|
| At 4,000 rpm||51 mph*|
|Trailer capacity||1/2 ton (approx)|
|Maximum gradient, loose sand|
| Without trailer||24° (45% or 1 in 2.25)|
| With trailer||12° (20% or 1 in 5)|
|Depth of water forded||1 ft 7 in|
|Fuel capacity||9 gal|
| On roads||17 mpg|
| Cross-country (approx)||12 mpg|
* This speed, it is stated, is only to be attempted in exceptional circumstances.