The main dimensions of the connecting rod and piston group are shown in Figure 1
The piston is cast aluminum
The piston weight is strictly maintained during manufacturing. Therefore, when assembling the engine, it is not necessary to select pistons of the same group by weight.
By outer diameter, the pistons are divided into five classes (A, B, C, D, E) with 0.01 mm increments. The outer surface of the piston has a complex shape.
It is barrel-shaped in height and oval in cross-section.
Therefore, the piston diameter must be measured only in the plane perpendicular to the piston pin, at a distance of 55 mm from the piston bottom.
According to the diameter of the hole for the piston pin, pistons are divided into three classes (1, 2, 3) through 0.004 mm.
The classes of piston diameters and holes for the piston pin are stamped on the piston bottom.
Repair size pistons are manufactured with an outer diameter increased by 0.4 and 0.8 mm.
The bottoms of these pistons are marked with a triangle or square.
The triangle corresponds to an increase in the outer diameter by 0.4 mm, and the square - by 0.8 mm.
The arrow on the piston bottom shows how to correctly orient the piston when installing it in the cylinder. It should be directed towards the camshaft drive.
The piston pin is steel, hollow, floating type, the tester rotates freely in the piston bosses and connecting rod bushing. The pin is fixed in the piston with two steel retaining rings.
By outer diameter, the pins are divided into three classes through 0.004 mm. The class is marked with paint on the end of the pin: blue mark - first, green - second, and red - third class.
Piston rings - made of cast iron. The upper compression ring - with a chromed barrel-shaped outer surface.
The lower compression ring is a scraper type. Oil scraper ring — with chromed working edges and with a coil spring (expander).
Rings of repair sizes are marked with a digital number "40" or "80", which corresponds to an increase in the outer diameter by 0.4 or 0.8 mm.
Connecting rod — steel, forged. The connecting rod is machined together with the cover and therefore they are not interchangeable separately.
To avoid mixing up the covers and connecting rods during assembly, they are stamped with number 6 (see Figure 2) of the cylinder in which they are installed.
During assembly, the numbers on the connecting rod and cover must be on the same side
A steel-bronze bushing is pressed into the upper head of the connecting rod.
By the diameter of the hole in this bushing, the connecting rods are divided into three classes in 0.004 mm increments (the same as pistons). Number 5 of class is stamped on the upper head of the connecting rod.
By the weight of the upper and lower heads, the connecting rods are divided into classes (table), marked with paint on the connecting rod rod.
The engine must be equipped with connecting rods of the same class by weight. The connecting rod weight can be adjusted by removing metal from the bosses on the heads to the minimum dimensions of 16.5 and 35.5 mm (Figure 3).
Connecting rod classes by the weight of the upper and lower heads
Since the 2012 release, the weights of the connecting rod heads have changed slightly
Piston to cylinder selection
The calculated minimum clearance between the piston and the cylinder (for new parts) is 0.025-0.045 mm.
It is defined as the difference between the minimum cylinder size and maximum piston size and is ensured by installing pistons of the same class as the cylinders.
The maximum allowable gap (due to wear of parts) is 0.15 mm.
If the gap of a previously used engine exceeds 0.15 mm, then it is necessary to re-select the pistons for the cylinders so that the gap is as close to the calculated one as possible.
Spare parts are supplied with pistons of classes A, C, E.
These classes are sufficient for selecting a piston for any cylinder during engine repair, since pistons and cylinders are divided into classes with a small overlap of sizes.
For example, a piston of class C can fit cylinders of classes B and D.
Disassembly and assembly
Remove the piston pin retaining rings from the piston, remove the pin and disconnect the connecting rod from piston.
Remove the piston rings.
The connecting rod bolts are pressed into the connecting rod.
Therefore, in order not to disturb the fit of the bolt in the connecting rod, it is not allowed to press the bolts out of the connecting rods when disassembling the engine and the connecting rod-piston group.
If some parts of the connecting rod-piston group are not damaged and slightly worn, they can be reused.
Therefore, when disassembling, mark them so that later you can assemble the group with the same parts and install it in the old engine cylinder.
Assembly
Before assembly, match the pin to the piston and connecting rod.
For new parts, the class of holes for the pin in the connecting rod and piston must be identical to the class finger.
For used parts, for proper mating, it is necessary that the piston pin, lubricated with engine oil, enters the piston or connecting rod hole from a simple press of the thumb (Figure 4) and does not fall out of it if you hold the piston as shown in Figure 5.
Replace the missing pin with another one from the next category. If a third category pin was inserted into the piston, replace the piston pin and connecting rod.
Assembly of the connecting rod and piston group is performed in the reverse order of disassembly.
After installing the piston pin, lubricate it with engine oil through the holes in the piston bosses.
Install the piston rings in the following order.
Lubricate the grooves on the piston and piston rings with engine oil.
Orient the piston rings so that the lock of the upper compression ring is located at an angle of 45˚ to the axis of the piston pin, the lock of the lower compression ring is at an angle of approximately 180˚ to the axis of the lock of the upper compression ring, and the lock of the oil scraper ring is at an angle of approximately 90˚ to the axis of the lock of the upper compression ring.
Install the lower compression ring with the groove down (See Figure 1). If the ring is marked "Top" or "TOP", install the ring with the mark facing up (towards the piston bottom).
Before installing the oil scraper ring, check that the joint of the spring expander is located on the side opposite the ring lock.
Checking the technical condition
Clean the piston from carbon deposits and remove all deposits from the piston and connecting rod lubrication channels.
Carefully inspect the parts. Cracks of any kind on the piston, piston rings, pin, connecting rod and its cover are not allowed.
If there are deep scratches on the working surface of the liners, replace the liners with new ones.
Check the clearance between the piston rings and grooves with a set of feeler gauges, as shown in Figure 6, inserting the ring into the corresponding groove.
The calculated clearance (rounded up to 0.01 mm) for new parts is 0.04-0.07 mm for the upper compression ring, 0.03-0.06 mm for the lower one and 0.02-0.05 mm for the oil scraper ring.
The maximum permissible clearances for wear are 0.15 mm.
Check the clearance in the piston ring lock with a set of feeler gauges, inserting the rings into a gauge (Figure 7) having a hole diameter equal to the nominal diameter of the ring with a tolerance of 0.003 mm.
For normal size rings with a diameter of 82 mm, gauge 67.8125.9502 can be used.
The gap should be within 0.25-0.45 mm for all new rings. The maximum allowable gap when worn is 1 mm.
