Since the 50s, in the USSR, the production of stationary engines was carried out, which are widely used in civilian and military spheres. The key developer and manufacturer of such engines was the motor plant in the city of Ulyanovsk. By the name of the plant, all engines had a UD index - this meant a reduction from the Ulyanovsk engine, and for the method of starting from a foot starter - “Top-top”.
Total information
The first serial samples of UD engines were equipped with a lower valve gas distribution scheme. Such a scheme provided the simplicity of engine design, but did not have reserves for modernization. At the end of the 60s, a family of engines based on the units of serial engines ZAZ-966 from cars of the Kommunar plant appeared in the plant’s production program. The family included two units:
- The UD-15 engine with one cylinder.
- Motor UD-25 with two cylinders.
Both engines had forced air cooling and overhead valves. In fact, the UD-25 engine was half the standard Zaporozhets motor. The technical documentation indicates the power of 12 horsepower. It should be borne in mind that the power indicators of UD engines are values during long-term operation. This is an important moment in identification.
Currently, the production of both types - the UD-25 and UD-15 engine is discontinued. They can be purchased at sales of decommissioned army equipment complete with various units. The most common fixed installation with a UD engine is a generator station. The photograph below shows just such a design - the AB-4 army generator.
Version with electric starter
Modification UD-25G, equipped with a cast transition sump. On one side, the crankcase was attached to the engine housing, and a generator was installed on the other side. There was a landing hole for the ST-351B electric starter on the transitional crankcase. The starter was powered by a rechargeable 12-volt battery, which was installed on a special pallet. The engine flywheel was equipped with a ring gear and a special disconnect clutch. The photo shows the flywheel housing of the UD-25G engine.
Optionally, such engines were equipped with a sealed and shielded ignition system. Thanks to this improvement, the system worked smoothly in the rain and did not create radio interference. The weight of the UD-25G engine was 66 kg.
Gear motor
Version UD-25S, equipped with a gearbox RO-2. Carter single-stage gearbox stood directly on the engine. The gearbox reduced the speed by more than two times. Such a unit was widely used to drive various mechanisms that required a reduced speed for operation.
Among such devices were various centrifugal pumps, compressors, railway railcars, road and agricultural machinery. The weight of the gearbox UD-25S is 61 kg.
Gearbox Maintenance
The UD gear motor is a fairly high-load unit, which is not recommended for operation at minimum speed. The reason lies in the centrifugal clutch, which starts to work only after 1,000 revolutions. Up to this point, slip clutches slip, leading to their premature wear. The ultimate RPM speed is 3,000 per minute. It is at this speed that the speed controller is set at the factory. In the photo in the article, the nameplate of the UD-25 engine is visible.
The engine gearbox needs to constantly check the oil level, which must be carried out every 100 hours of operation. An oil change should be done every 400 hours. It is better to drain hot oil, so this work is done immediately after the engine stops.
Other engine options
UD-25 engines and their modifications were produced by a number of enterprises in the republics of the USSR:
- In the Kazakh SSR in the city of Petropavlovsk there was a plant that produced units under the designation PD or SK.
- In the Ukrainian SSR in Kharkov, the production of similar motors under the SM index was in progress.
These motors were used along with the Ulyanovsk power units and had similar modifications. In the photo in the article, you can see the generator set with the UD-25 engine.
Repair and service
The UD-25 engine is capable of operating on any type of gasoline with an octane rating ranging from 70 to 76. The design of the engine allows the use of leaded gasoline. To lubricate the engine depending on the ambient temperature, winter or summer oil must be used. Neglecting the type of oil leads to insufficient lubrication of the components and engine failure.
Before each engine start , check the oil level in the crankcase and top up in a timely manner. When operating the engine, it is necessary to carry out service work complexes every 100 and 200 hours. With little maintenance, it is necessary to clean the candles and lubricate the components of the magneto and ratchet mechanism of the kick starter.
Great maintenance of the UD-25 engine involves removing the cylinder head and checking the tightness of the valves. In this case, the condition of the rings and mirrors of the cylinders, the absence of backlash of the piston fingers are checked. The combustion chambers are cleaned of possible deposits and the oil in the crankcase is replaced. In this material, you can consider the UD-25 engine from above.
During the operation of the motor, it is necessary to check the gap in the valve drive mechanism every 100 hours of operation, which should not exceed 0.2 mm. Check is carried out by the probe on the cold engine.
When the mirrors of the cylinders are worn, they are not polished, but are changed entirely. One of the features of UD-25 engine repair is the correct installation of valve followers. In one of them, there is a through channel inside, which serves to supply oil to the valve box. At installation, this pusher should be the fourth in a row from the flywheel.