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The
factory of Zbrojovka company, in the Moravian town Brno (say: Bruno),
Czech republic, has a long history as a metal foundry since 1864. In the
second world war this factory was a forced dependant of the German company
"Flugzeugwerke Ostmark", or "Airplane works Ostmark", what used the
Zbrojovka plant in the Brno district Vankova for the production of
airplane engines and components. Most of the factory's facilities were
damaged by Allied bombs during the war. Directly after WW II, the
development of a prototype of the Zetor 25 started. The engineers were
from the former Zbrojovka car plant. This design team was under
supervisory of engineer F. Musil.
model 25
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The 25 was a modern Diesel tractor, developed in the years 1945 - 1948. The engine was a
two cylinder four stroke engine with 105 mm bore and 120 mm stroke. It had indirect fuel injection,
with mechanical dispensers instead of commonly used compressed air dispension or hotbulbs.
This Diesel was a good engine, that was most
competitors ahead in technique and lifespan. The design style was
classic, but modern technology and constructions were used.
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The transmission was equipped with 6 forward
and 2 reverse speeds, divided into two groups.The PTO shaft made 540 rpm
conform the European standard. The belt pulley, used to drive things like
a threshing machine or a sawmill, was mounted on the same shaft as the
PTO, using a bevel gear. These tractors had also independent steering brakes to decrease turning
radius. Other standard equipment was a differential lock, a mechanism
that is very useful, but was not seen on most tractors of
that time. Most of these tractors had a mechanical hitch.
model 15
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In 1947, a one cylinder model came from
Brno. It was targeted as a more affordable alternative for the
25 two cylinder, with 15 hp. It had 120 mm bore and
140 mm stroke, that was also using the four stroke Diesel proces.
The transmision had 5 speeds forward and 1 reverse. It was probably a predecessor
of the transmission of the Super series, they had the same
belt pulley drive.
This model was quite
old-fashioned compared with the 25. It had to start using a decompressor, and a
glow fuse. This is probably the rarest Zetor there is, only
1800 were built. |
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The
major design of both engines was probably a joint-engineering project with
Tatra, what was developing air cooled engines with identical bore and
stroke. The cylinder liners of the two cylinder were replacable with those
of the early Tatra engines.
Worth noticing is
that the top speed of the 25 was about 30% higher than usual in the
40's and 50's. The transmission of the 15 had lower speeds, it had
smaller tires and a lower engine speed of 1500 rpm. (see table
below)
model 25 A
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In 1948, the 25 was succeeded by the model 25 A. The tractor was updated in many details, for example: the metal
pan seat was replaced by a leather seat, the front of the bonnet was redesigned, the brake pedals and gas throttle
were placed more ergonomic, and the side exhaust was now mounted upright, to prevent setting your hay on fire.
Also the durability, mostly of the transmission, was improved by adding 76 kg of material to crucial parts
of the construction. The front axle was a new gate formed one, what increased the ground clearance
with about 10 centimeters. |
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Anyway, The
A-model (All-round) was still not very suitable for row crops, its ground
clearance was too small. The A model had a low center of gravity, so that
the tractor would be more stabile on hill slopes. This made it suitable
for the cattle farmers, that used it just for towing and mowing in the
Czech mountains. The model A had a hydraulic hitch as option.
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The halftrack 25 A
'polopasovy'
Another factory installed modification for the 25 A was the half-track. A belt was running
over the rear wheels and a supplementary axle, stretched by springs. The belt
was built up from two cables, with iron beams between them.
The tractor had a steered front axle, but the independent foot
brakes were needed to turn tight. The advantages of the halftracks
are best used in mud, snow and forest. |
model 25 K
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At the same time, another model was introduced as a row crop, model 25 K. It had much bigger rear wheels, and a
higher front axle. Longer turning columns of the front axle gave it about 19 centimeters (7.5") more ground clearance.
A hydraulic hitch was standard.
The transmission of the K had a closer gear ratio spacing, for better performance
in the field. It had 4 gears in the important field speed range of 4 to 12 km/h. The closer gear ratio spacing
also resulted in a lower top speed of 20.3 km/h.
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The
model
K (Kultivaci, cultivating) was targeted to the crop farmers on flat land, what would use the tractor for tillage, and row crop care.
For row crop use, tires of size 9x36 were used (blue tractor). When it was used for tillage, the K came with 13x28
tires. (brown tractor). The differential lock was an advantage for tillage, the independent brakes were advantageous
in row crop.
Prototypes based on the
T25 series
The Zbrojovka engineers developed
several prototypes (partly) based on the 15, 25 and Super models. The most
interesting ones are not serial produced, but they were design studies for
the later Unified Range 1, one
of the most modern tractor series of its time.
Zetor T18
A one cylinder tractor
for row crop care. It was designed to carry equipment like sprayers and
hoes
Zetor 18
A small one cylinder crawler tractor, what can be seen
as the predecessor of the UR1 series.
Zetor 26
had
a two cylinder engine with enlarged stroke. It was produced in
around 1955. The engine had a bore/stroke of 105x130 mm and
a displacement of 2251cc. It's power was 28 hp at 1600
rpm.
Zetor 30
was ready for serial production
in 1949. This tractor was the same as the 25, except the cylinder heads.
The Zetor 30 was one of the world's first tractors with direct Diesel
injection. It was promptly awarded on the Prague Agricultural show with a
gold medal. However, the Communist Central Office decided that the 30
would not be serial produced, they decided that a tractor with higher
power should be developed...(subject changes not to politics
here)
A three cylinder tractor
also
appeared in this era. The engine was a combination of one and a
half T25 engines. It's power was 29 hp at 1400 rpm.
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Specifications of the
Zetor T series |
|
model |
15 |
25/25 A |
25 K |
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production |
1947-1949 |
1946-1948/
1961 |
1948-1961 |
|
type of engine |
4 stroke OHV, indirect injected
Diesel,
water cooled |
|
No. of cylinders |
1 |
2 |
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bore x stroke (mm) |
120 x 140 |
105 x 120 |
|
displacement (CC) |
1583 |
2078 |
|
power (hp) |
15 |
25 |
|
at rpm |
1500 |
1800 |
|
transmission
speeds 1
(km/h)
2
3
4
5
6
reverse
low
high |
3.9
5.6
8.2
13
22.3
-
2.8
- |
3.4
5.2
7.8
13
20
32
2.3
9.0 |
4.3
5.6
7.2
11.9
15.6
20.3
3.0
7.7 |
|
PTO |
dependent 540 rpm |
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belt pulley |
yes |
|
hydraulic hitch |
option |
standard |
|
tires
front
rear |
5.50 x 16
9 x 24 |
5.50 x 16
11.25 x 24 |
5.50 x 16
9x 36/13x 28 |
|
trackwidth (cm) front
rear |
127-145
127-145 |
120-150
120-150 |
122-154
115-146 |
|
wheelbase (cm) |
156 |
190 |
|
weight (kg) |
1400 |
1750/1826 |
1955 |
The 25 A and K production stopped in 1961, when a total of 158.570 units were built of the 25. Thousands of them
are still running, or even in use on farms, at most in Scandinavia. The 25 two cylinder engine is the grandfather of
the nowadays range 2, 3 and 4 engines, so its 'spirit' lives on.
Super 35 - Super 50
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ZETOR came with their first four cylinder tractor in 1955, called the Super 35. Its engine
was a direct clone of the one of the 25, and was used in the models 35 super, and Super P.
The updated Super 35 was called
Super 50, introduced in 1960. It had a power output of 50 hp, also at 1500
rpm. The transmission was in the same style as the one of the model
15, the place of the belt pulley, and the number and gear ratios
were similar. The 5 speed had a solid and simple
construction. |
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The Super series had also some nice standard features,
such as an independently leaf sprung front axle, differential lock, air
compressor, and an engine oil cooler. This cooler was an advantage
for stationary work, such as driving a threshing machine on the belt
pulley. Optional was a drivers cab with heater.
the Super
P
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The 42 hp engine was also used in a tracked tractor, the Super P. Its weight was 4200 kg, what means a
specific weight of 100 kg per HP.
The transmission had other gear ratios than the wheeled super, it was
made for heavy haulage at between 3 and 7 km per hour. Its maximum speed was 15 kph. The folder speaks of a fuel use of
17.5 litre per Hectare, or 9 litre of Diesel per hour at a ploughing depth of 30 cm.
The
demand for tracked tractors in the fifties consisted from the lack of hitch-hydraulic weight transfer systems
and the slow development of good tractor tires. |
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A winch was an option when it was used in forestry to
haul trees trough the woods.The agricultural versions had standard a
hydraulic hitch. It was also used with optional dozer blade for landscaping and
earthmoving, and for the deep tillage what land reclaim projects demanded.
"Tough guy..."
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specifications of
the Zetor Super |
|
model |
35 Super |
50 Super |
Super P |
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production |
1955-1960 |
1960-1968 |
1956-1958 |
|
type of engine |
4 stroke OHV Diesel, indirect
injected, water cooled |
|
No. of cylinders |
4 |
|
bore x stroke (mm) |
105 x 120 |
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displacement (CC) |
4,156 |
|
Power HP |
42 |
50 |
42 |
|
at rpm |
1500 |
|
transmission speeds 1
(km/h)
2
3
4
5
R |
3.92
5.15
7.42
12
24
? |
2.4
3.14
4.5
7.3
14.6
2.4 |
|
PTO |
dependent 540 rpm |
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belt pulley |
yes |
|
hydraulic hitch |
yes |
|
trackwidth |
120-150 |
173 |
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Tires front
rear |
6.00 x 20
13 x 28 |
tracks |
|
weight (kg) |
2550 |
4200 |
A local agricultural contractor had two Zetor 50 Supers in the fifties. These tractors left quite an
impression on the people of that time. My neighbour remembers them as "two of those real huge Zetors pulling the
manure spreaders" These tractors were extremely tough pullers, because of the low engine speed and big displacement. Only
the real hog could wreck these solid machines without a sledge hammer.
The Supers are
built from 1955. The Super 35 was succeeded in 1960 by the Super 50, which was produced to
1968. It was sold as affordable alternative for the UR 1 type 4011, which
was more productive and economic in use. From 1955 to 1968, 106.881 tractors
were made in the Super series.
© DmdB 2001 |
