"Gazelle" Gas-2705>> The engine>> Engines ZMZ-4025,-4026>> The krivoshipno-shatunnyj mechanism
Pistons are cast from высококремнистого an aluminium alloy and thermally processed. A piston head — cylindrical with the flat bottom. On a cylindrical surface of a head three flutes are pierced: in two top are established компрессионные rings, and in bottom — маслосъемное. In a flute under маслосъемное a ring from both parties cuts are executed that rubbing surfaces of a skirt of the piston from heat going from the bottom of the piston did not overheat. On the same cuts the oil removed маслосъемным by a ring is taken away in картер the engine. Under a flute for маслосъемного rings the facet and on it — on two apertures from both parties which too serve for tap of the oil accumulating under маслосъемным by a ring is executed.
Piston skirt oval in cross-section section and бочкообразная in the longitudinal. The big axis of an oval is located in a plane, a perpendicular axis of a piston finger. The size of ovality of the piston makes 0,39 0,43 mm. The greatest diameter of a skirt of the piston settles down on 8 mm below an axis of a piston finger. Diameter of a skirt smoothly decreases and in a direction to the bottom and in an opposite direction: the maximum reduction of diameter by a facet edge under the bottom flute makes 0,034—0,064 mm, on the bottom edge of a basic part of a skirt — 0,050—0,080 mm. The aperture axis under a piston finger is displaced from an average plane on 1,5 mm in right (on a car course) the party for reduction of noise from a rearrangement of the piston from one wall of a sleeve to another at change of a direction of movement of the piston (upwards — downwards).
In a piston body between the bottom flute and an aperture under a piston finger the steel thermoregulating insert serving for reduction of deformations of the piston at heating to working temperature and reduction of initial assembly backlashes at assemblage is filled in. Pistons are established in sleeves of the same dimensional group with a backlash of 0,024-0,048 mm.
For maintenance of a demanded backlash pistons and sleeves are divided (on diameter) into five groups, designated by the corresponding letter which is beaten out on the bottom of the piston and (tab. 4.1) is put on an external surface of the bottom part of a sleeve.

Table 4.1. Dimensional groups of pistons and sleeves
Dimensional groups of pistons and sleeves
Group designation
Diameter, mm
The piston
The piston

For improvement extra earnings the piston surface is covered (электролитическим in the way) by a layer of tin in the thickness of 0,001 0,002 mm.
That pistons worked correctly, they should be established in cylinders in strictly certain position. For this purpose on one of piston lugs there is an inscription "BEFORE". According to this inscription the piston the specified party should be turned to a forward part of the engine.
Piston rings. Kompressionnye rings are cast from pig-iron: top — from the high-strength pig-iron possessing high elasticity; bottom — from grey pig-iron. Top компрессионное the ring works in most severe conditions (at high temperature and pressure, and also at a greasing lack). For wear resistance increase its external surface adjoining to the cylinder, is covered by a chrome layer. The chrome layer considerably increases service life of the top ring. It promotes also to increase in service life of the bottom ring of the cylinder.

Fig. 4.4. Installation of piston rings on the piston: 1 — top компрессионное a ring; 2 — bottom компрессионное a ring; 3 — a ring disk; 4 — an axial dilator; 5 — a radial dilator

The external cylindrical surface bottom компрессионного rings is covered by a layer of tin in the thickness of 0,006-0,012 mm (or all surface of a ring has a phosphatic covering) that improves to its extra earnings. On an internal cylindrical surface bottom компрессионного rings there is a bore (fig. 4.4) thanks to which the new rings established in the cylinder, are turned out and adjoin to the cylinder only an edge a little. It accelerates and improves to extra earnings of rings to a cylinder mirror. On the piston the ring should be established bore up. Infringement of this condition causes sharp increase of the expense of oil and дымления the engine. The top ring of bore has no.
Maslosemnoe ring — modular, four- or three-element. The four-element ring consists of two steel ring disks of 3 and two steel dilators: axial 4 and radial 5. Three-element маслосъемное the ring consists of two steel ring disks and one steel two-functional dilator. The working cylindrical surface (adjoining to the cylinder) ring disks is covered by a layer of chrome in the thickness of 0,080-0,130 mm.
Height компрессионных rings — 2 mm, маслосъемного in gathering — 4,9 mm. The lock of rings — a straight line.
Piston fingers of floating type (they are not fixed neither in the piston, nor in a rod) became made from низколегированной by a method of cold disembarkation. The external surface of a finger is subjected углеродонасыщению on depth of 1-1,5 mm and tempered by heating ТВЧ to hardness HRC 59—66. External diameter of a finger — 25 mm.
To warn knock of fingers, them select to pistons with the minimum backlash, admissible for greasing conditions. As linear expansion of a material of the piston approximately in 2 times more than at a finger at a room temperature the finger enters into apertures of lugs of the piston with a tightness.
The finger steals up to a rod with a backlash from 0,0045 to 0,0095 mm. For convenience of selection fingers, rods and pistons are divided into dimensional groups (tab. 4.2).

Table 4.2. Dimensional groups of fingers, pistons and rods
Dimensional groups of fingers, pistons and rods
Diameter, mm
In a piston lug
In the rod plug
Fingers and rods
The piston
The white
The green
The yellow
The red

Fingers and rods are marked by a paint: a finger — on an aperture or at an end face, a rod — on a core of a piston head, the piston — the Roman figures (knockout) on the bottom or a paint on a weight lug. To select a piston finger to a rod and the piston follows, as it is specified in subsection «engine Repair».
The exact size of weight of a finger is provided with keeping of admissions for the sizes at manufacturing.
The finger is kept in the piston by two lock rings made of a round spring wire in diameter of 2 mm. Rings have the short moustache put aside. Lock rings establish by means of flat-nose pliers so that the short moustache has been turned outside.
Rodssteel shod with a core двутаврового sections. In a piston head of a rod запрессована the thin-walled plug from оловянистой bronze. A krivoshipnaja head of a rod — demountable. The cover кривошипной heads fastens to a rod two bolts with шлифованной a landing part.
Bolts of fastening of covers and a nut шатунных bolts are made of the alloyed steel and thermally processed.
Nuts шатунных bolts are tightened by the moment 68—75 Н·м (6,8—7,5 кгс·м) and stopped by hermetic "Unigerm-9".
Covers of rods are processed in gathering with a rod and consequently they cannot be rearranged from one rod on another. For prevention of a possible error on a rod and on a cover (on a lug under a bolt) serial numbers of cylinders are beaten out. They should be located on the one hand. Besides, deepenings for fixing ledges of loose leaves also should be in a cover and a rod on the one hand.
In a core of a rod at кривошипной heads there is an aperture in diameter of 1,5 mm through which greasing of a mirror of the cylinder is made. This aperture should be directed to the right party of the engine, i.e. Aside, opposite to a camshaft. At correct assemblage number "24", выштампованное on an average shelf of a core of a rod, and also a ledge on a rod cover should be turned to the forward party of the engine.
For maintenance of dynamic steadiness of the engine the total weight of the piston, a piston finger, rings and a rod, established in the engine, can have a difference on cylinders no more than 12 г that is provided with selection of details of the corresponding weight. On details the difference in weight can be: pistons — 4 г, rods — 18 г, piston fingers — 2 For maintenance of the above-stated difference in weight of details in one engine (12) rods on weight break into four groups and should steal up for one engine with a difference no more than 5
The cranked shaft - is cast from high-strength pig-iron, has five support, in gathering with a flywheel and coupling is dynamically balanced (an admissible disbalance — no more than 35 г·см). Diameter of radical necks — 64 mm, шатунных — 58 mm. Shatunnye necks hollow. Cavities in шатунных necks are closed by carving stoppers and intended for additional clearing of the oil arriving on шатунные of a neck. Under the influence of the centrifugal forces arising at rotation of a cranked shaft, in cavities шатунных necks отлагаются metal particles of products of the deterioration, containing in oil.
Oil шатунных necks is brought to cavities on apertures in cheeks of a shaft from a ring flute on loose leaves of radical necks of a cranked shaft. To radical necks oil arrives from an oil highway on channels in block partitions.

Fig. 4.5. The forward end of a cranked shaft: 1 and 2 — persistent washers; 3 — the bearing loose leaf; 4 — a bearing cover; 5 — a pin; 6 — a washer persistent

Axial moving of a cranked shaft is limited to two persistent steel-aluminium washers 1 and 2 (fig. 4.5), located on either side of the forward radical bearing. The forward washer is turned by 1 antifrictional layer to a steel persistent washer 6 on cranked to a shaft, a back washer 2 — to a cheek of a cranked shaft. The forward washer is kept from rotation by two pins 5, запрессованными in the block and a cover of the radical bearing. The acting ends of pins enter into washer grooves. The back washer is kept from rotation by the ledge entering into a groove at a back end face of a cover of the radical bearing. The size of an axial backlash makes 0,125—0,325 mm.
On the forward end of a cranked shaft on шпонках the steel persistent washer, a gear wheel of a drive of a camshaft, маслоотражатель and a nave of a pulley of a cranked shaft are established. All these details are pulled together by a bolt screwed in a forward end face of a cranked shaft. The shponochnyj groove in a pulley nave is condensed with a rubber stopper. To a nave six bolts the pulley of a cranked shaft from which by two belts are resulted in rotation the fan, крыльчатка the water pump and a generator pulley fastens. On a pulley the special device — демпфер is mounted, the employee for clearing крутильных fluctuations of a cranked shaft thanks to what noise decreases and working conditions of gear wheels of a drive of a camshaft are facilitated. Демпфер consists of a pig-iron disk, напрессованного through an elastic (rubber) lining on a cylindrical ledge of a pulley of a cranked shaft.

Fig. 4.6. Definition of the top dead point

On a pulley of a cranked shaft one label, and on a disk демпфера — three labels (fig. 4.6), employees for definition of the top dead point (ВМТ) and ignition installations is put.
Label on a pulley and the third label on a disk демпфера should be against each other. Mutual mixture of labels specifies in failure демпфера. At combination with an edge-index on a cover of distributive gear wheels of the third label (in a rotation direction) on a disk демпфера pistons of the first and fourth cylinders are in ВМТ. The second label corresponds to position 5 ° to ВМТ and serves together with the third label for ignition installation on the idle engine.
The first label corresponds to position 12 ° to ВМТ and serves together with the second and third labels for the control of correctness of installation of ignition on the working engine.
The forward end of a cranked shaft is condensed by a rubber cuff with маслоотражателем, запрессованным in a cover of distributive gear wheels. On маслоотражателе is available отбортовка, taking away the oil which is flowing down on a wall of a cover. For simplification of work of a cuff before it on cranked to a shaft one more is established маслоотражатель.
Reliable work of a cuff after a partition is provided with good centering of a cover of distributive gear wheels (the subsection «engine Repair» see).
The back end of a cranked shaft is condensed by stuffing from the asbestine cord impregnated with antifrictional structure and covered with graphite.
Stuffing is put in flutes of the block of cylinders and the special holder who fastens two hairpins to the block. On a neck of a cranked shaft under stuffing is available микрошнек, and before stuffing — a crest serving for rejection of oil from a zone of consolidation. Joints of the holder are condensed by rubber linings of the G-shaped form. In a back end face of a cranked shaft the nest for installation of the ball-bearing of a primary shaft of a transmission is chiseled.
The flywheel is cast from grey pig-iron. It fastens to a flange on the back end of a cranked shaft four шлифованными bolts.
The moment of an inhaling of nuts of bolts — 76 83 Н·м (7,6—8,3 кгс·м). Nuts законтрены отгибной a plate. On a flywheel напрессован a gear rim for start-up of the engine by a starter. Before assemblage with cranked shaft a flywheel (tab. 4.3) statically balance.

Table 4.3. A disbalance of rotating details, admissible at engine assemblage
Disbalance of rotating details, admissible at engine assemblage
Balancing method
Admissible disbalance,   г·см, no more
Way of elimination of a disbalance
Cranked shaft in gathering with stoppers
The dynamic
40 on each end
Metal drilling in a radial direction from counterbalances on 1,4, 5 and 8th cheeks a drill in diameter of 8 mm on depth of 45 mm
Flywheel and gear wreath
The static
Metal drilling from outside coupling fastenings on radius of 146 mm a drill in diameter of 12 mm on depth no more than 15 mm
Cranked shaft, flywheel and coupling in gathering
The dynamic
35 on the back end
Metal drilling from outside coupling fastenings on radius of 146 mm a drill in diameter of 12 mm on depth no more than 15 ммВысверливание metal from a flywheel from outside couplings on radius of 151 mm a drill in diameter of 12 mm on depth no more than 12 mm; distance centre to centre apertures - not less than 16 mm
Press a disk of coupling with a casing in gathering
The static
Drilling of metal from the lugs aligning springs, a drill in diameter of 11 mm on depth no more than 25 mm taking into account a drill cone; at repeated installation of knot on the balancing machine tool the disbalance 100 г·см is supposed
Pulley-dempfer of a cranked shaft with a nave in gathering
The static
Drilling of metal from a forward end face of a pulley on radius of 64 mm a drill in diameter of 10 mm on depth no more than 9 mm

To a back end face of a flywheel six bolts attach a coupling casing. On a flange of a casing of coupling and a flywheel the label is beaten out "About". At engine assemblage both labels should be combined not to break balancing of a cranked shaft.
Loose leaves. Radical and шатунные bearings of a cranked shaft consist of the thin-walled interchangeable loose leaves made from малоуглеродистой of a steel tape with a thin layer antifrictional высокооловянистого of an aluminium alloy. The thickness of the radical loose leaf fluctuates within 2,233—2,240 mm, and шатунного — 1,738—1,745 mm. In each bearing it is established on two loose leaves. Axial moving and проворачиванию loose leaves in beds of the block or in rods is interfered by fixing ledges on the loose leaves, entering into corresponding grooves in beds of the block or in rods.
All radical loose leaves have a ring flute for a continuous food by oil шатунных necks of a cranked shaft. In the middle of radical loose leaves there is an aperture through which oil to bearings from the channel in block bed moves. Apertures in шатунных loose leaves coincide with apertures in rods. For preservation взамозаменяемости and preventions of errors at installation of new loose leaves on all radical and brass loose leaves are made apertures. Ширинa radical loose leaves — 25,5 mm, шатунных — 28,5 mm. The diametrical backlash between a neck and loose leaves makes 0,020—0,073 mm for radical and 0,010—0,063 mm for шатунных bearings.
For maintenance of the specified backlashes and an exception of deformation of details of a nut шатунных bolts, hairpins of fastening of covers of radical bearings tighten динамометрическим a key with the moment specified above.