The clearance between the oil control ring and the piston groove should be within 0.135–0.335 mm.
The ring gap clearances should be within 0.3–0.7 mm for compression rings and 0.3–1.0 mm for oil control rings.
The size groups of pistons, connecting rods and pins are given in the table at the end of the article.
Pins and connecting rods are marked with paint: the pin in the bore, the connecting rod on the shank near the upper eye.
A Roman numeral showing the piston group is stamped on the piston crown.
The pin must not fall out of the connecting rod eye if tilted at approximately 45°.
The mass difference between pistons assembled with connecting rods, pins and piston rings fitted to one engine must not exceed 12 g.
Dismantling and inspection of the connecting rod and piston group
Using a ring expander, remove the piston rings. If no expander is available, the rings can be removed by carefully spreading them at the gaps.
Remove the circlips from both sides of the piston.
Drive out the piston pins with light hammer blows through drift 1. Withdraw connecting rod 2 from piston 3.
Remove the remaining pistons from the connecting rods in the same way.
Inspect the pistons. If there is scoring, burning or deep scratches, replace the pistons.
Measure the piston diameter. If it is less than 91.9 mm, replace the piston.
The piston diameter is measured in a plane perpendicular to the gudgeon pin axis, 8.0 mm below the pin axis.
The piston is fitted in the cylinder with a clearance of 0.024–0.048 mm.
To ensure the clearance value, pistons are divided by diameter into five size groups: A, B, V, G and D.
The letter marking is stamped on the piston crown.
When matching the piston to the cylinder, the above clearance must be ensured.
The maximum permissible clearance between piston and cylinder is 0.25 mm.
The clearance between piston and cylinder can be determined by measuring the piston and cylinder.
Spare parts include pistons of two repair sizes: with diameter increased by 0.5 mm and by 1.0 mm.
Measure the clearance between the piston ring and the piston groove at several points around the piston circumference.
The clearance should be within 0.05–0.087 mm for compression rings and 0.115–0.365 mm for the oil control ring.
If the clearances exceed those specified, replace the rings or pistons.
Measure the ring gap clearances.
To do this, insert the ring into the cylinder and advance it with the piston used as a drift so that the ring sits squarely in the cylinder without tilting.
Measure the ring gap with a feeler gauge; it should be within 0.3–0.6 mm for compression rings and 0.5–1.0 mm for oil control ring rails.
If the gap exceeds that specified, replace the ring.
If the gap is smaller, the ring ends can be filed with a file clamped in a vice. The ring is then moved up and down over the file.
Check the fit of the piston pin in the connecting rod upper eye.
The clearance between the pin and the bush of the connecting rod upper eye should be within 0.0045–0.0095 mm.
Pins, pistons and connecting rods are divided into four size groups and marked with paint.
The pin is marked on the inner surface at one end, the connecting rod on the shank, the piston on the lower surface of one of the bosses, or a Roman numeral is stamped on the piston crown.
Lightly lubricate the piston pin with engine oil and insert it into the connecting rod upper eye.
The pin should enter the eye under thumb pressure, squarely, without sticking.
The connecting rod should rotate on the pin under its own weight from the horizontal position.
The pin must not slide out or fall out of the connecting rod eye under its own weight if the connecting rod is turned so that the pin is vertical.
The piston pin and connecting rod should be of the same or adjacent size groups.
Pistons with rings, pins and connecting rods assembled are matched by mass.
The mass difference for one engine must not exceed 12 g.
Inspect the connecting rod bearing shells. If they show scoring, scores, flaking, etc., replace them.
Fit the caps to the connecting rods and measure the diameter of the bore in the connecting rod lower eye.
The nominal bore diameter is 60+0.019 mm; the maximum permissible is 60.03 mm.
If the measured diameter exceeds the maximum permissible, replace the connecting rod with cap.
Measure the diameter of the bore in the bush of the connecting rod upper eye.
The nominal bore diameter is 22+0.007–0.003 mm; the maximum permissible is 22.01 mm.
If the measured diameter exceeds the maximum permissible, replace the connecting rod.
Assembly and installation of pistons with connecting rods
Assemble piston 4 with connecting rod 3. Before that, heat the piston to 60–80 °С.
Then quickly insert the connecting rod into the piston so that the inscription «Перед» (Front) on the piston and lug A on the connecting rod are on the same side, and press in piston pin 6.
Fit circlips 5.
Fit the piston rings onto the piston using the expander.
The upper compression ring bears the inscription «Верх» (Top); the ring must be fitted with this inscription towards the piston crown.
The lower compression ring has a groove on its inner face; the ring must be fitted with this groove upwards towards the piston crown.
Insert bearing shell 7 into the connecting rod lower eye; the locating lug on the shell must enter the recess in the piston lower eye.
Insert bearing shell 1 into connecting rod cap 2; the locating lug on the shell must enter the recess in the cap.
Lubricate the cylinder, piston 4, crankshaft big-end journal and bearing shells 1 and 7 with engine oil.
Turn the piston rings so that the gaps of the compression rings are 180° apart, the gaps of the oil control ring rails are also 180° apart and 90° to the compression ring gaps, and the gap of the oil control ring expander is 45° to the gap of one of the oil control ring rails.
Turn the crankshaft so that the big-end journal of the cylinder into which the piston is being fitted is at TDC.
Insert the piston with connecting rod into the cylinder; the inscription «Перед» (Front) on the piston boss must face the front of the engine (towards the camshaft drive).
To avoid damaging the cylinder bore, it is recommended to fit sleeves of soft material (e.g. pieces of rubber or plastic hose) over the connecting rod bolts.
Using a special ring compressor, compress the piston rings and push the piston into the cylinder with light blows of a hammer handle; the compressor must be pressed firmly against the block, otherwise the piston rings may break.
Push the piston down so that the connecting rod lower eye seats on the crankshaft big-end journal, and remove the hose pieces from the connecting rod bolts.
Fit connecting rod cap 2 onto the connecting rod bolts; the «Б» step on the connecting rod cap must be on the same side as the «А» lug on the connecting rod lower eye, and the cylinder numbers stamped on the connecting rod and cap must be on the same side.
- Tighten the connecting rod bolt nuts to a torque of 68–75 N·m (6.8–7.5 kgf·m).
- Fit the remaining pistons with connecting rods in the same way.
- Turn the crankshaft several times; it should rotate freely, without sticking.
Size groups of pistons, connecting rods and pins
| Pin diameter, mm | Bore diameter, mm | Marking | ||
|---|---|---|---|---|
| in connecting rod upper eye | in piston boss | of pin, connecting rod and piston | of piston | |
| 25.0000–24.9975 | 25.0070–25.0045 | 25.0000–24.9975 | White | I |
| 24.9975–24.9950 | 25.0045–25.0020 | 24.9975–24.9950 | Green | II |
| 24.9950–24.9925 | 25.0020–24.9995 | 24.9950–24.9925 | Yellow | III |
| 24.9925–24.9900 | 24.9995–24.9970 | 24.9925–24.9900 | Red | IV |
Nominal and maximum permissible dimensions, fits of the mating parts of the connecting rod and piston group of the mod. 402 engine
| Part name | Nominal diameter, mm | Mating part name | Nominal diameter, mm |
|---|---|---|---|
| Piston | 92.0+0.048 92.0−0.012 |
Cylinder liner | 92.0+0.084 92.0+0.024 |
| 1st repair size 92.5+0.048 92.5−0.012 |
1st size 92.5+0.084 92.5+0.024 |
||
| 2nd repair size 93.0+0.048 93.0−0.012 |
2nd size 93.0+0.084 93.0+0.024 |
||
| Upper compression ring | 2.0−0.012 height |
Piston | 2.0+0.075 2.0+0.050 groove width |
| Lower compression ring | 2.0−0.012 height |
Piston | 2.0+0.075 2.0+0.050 groove width |
| Oil control ring | 0.7−0.04 × 2 + 3.5−0.1 height of the two rails and expander |
Piston | 5.0+0.055 5.0+0.035 |
| Piston pin | 25.0−0.01 | Connecting rod | 25.0+0.007 25.0+0.003 |
| Piston pin | 25.0−0.01 | Piston | 25.0−0.01 |
| Connecting rod upper eye bush | 26.27+0.145 26.27+0.100 |
Connecting rod | 26.25+0.045 |
| Piston pin circlip | 2.0 ± 0.03 thickness |
Piston | 2.2+0.12 groove width |
| Connecting rod bearing shells | 61.5+0.019 − 2 (1.75−0.005) 61.5+0.019 − 2 (1.75−0.012) |
Crankshaft | 58.0−0.02 |
| Connecting rod | 36.0−0.25 36.0−0.35 lower eye width |
Crankshaft | 36.0+0.1 big-end journal width |
Nominal and maximum permissible dimensions, fits of the mating parts of the connecting rod and piston group of the mod. 402 engine
| Part name | Clearance, mm | Interference, mm | Maximum permissible, mm | |||
|---|---|---|---|---|---|---|
| min | max | min | max | clearance | dimension | |
| Piston (nominal) | 0.024 | 0.048 | — | — | 0.25 | 91.5 piston 92.15 liner |
| Piston (1st repair size) | 0.024 | 0.048 | — | — | 0.25 | 1st size |
| Piston (2nd repair size) | 0.024 | 0.048 | — | — | 0.25 | 2nd size |
| Upper compression ring | 0.05 | 0.087 | — | — | 0.15 | 2.1 groove width |
| Lower compression ring | 0.05 | 0.087 | — | — | 0.15 | 2.1 groove width |
| Oil control ring | 0.135 | 0.335 | — | — | — | — |
| Piston pin (in connecting rod) | 0.0045 | 0.0095 | — | — | — | 25.01 connecting rod upper eye diameter |
| Piston pin (in piston) | — | 0.0025 | — | 0.0025 | — | — |
| Connecting rod upper eye bush | — | — | 0.075 | 0.165 | — | — |
| Piston pin circlip | 0.17 | 0.35 | — | — | — | — |
| Connecting rod bearing shells | 0.01 | 0.063 | — | — | — | — |
| Connecting rod | 0.25 | 0.45 | — | — | — | — |
Size groups of cylinders and pistons
| Group | Cylinder diameter, mm | Piston diameter, mm |
|---|---|---|
| A | nominal size 92.036–92.024 |
nominal size 92.000–91.988 |
| 1st repair size * 92.536–92.524 |
1st repair size 92.500–92.488 |
|
| 2nd repair size ** 93.036–93.024 |
2nd repair size 93.000–92.988 |
|
| B | nominal size 92.048–92.036 |
nominal size 92.012–92.000 |
| 1st repair size 92.548–92.536 |
1st repair size 92.512–92.500 |
|
| 2nd repair size 93.048–93.036 |
2nd repair size 93.012–92.000 |
|
| V | nominal size 92.060–92.048 |
nominal size 92.024–92.012 |
| 1st repair size 92.560–92.548 |
1st repair size 92.524–92.512 |
|
| 2nd repair size 93.060–93.048 |
2nd repair size 93.024–92.012 |
|
| G | nominal size 92.072–92.060 |
nominal size 92.036–92.024 |
| 1st repair size 92.572–92.560 |
1st repair size 92.536–92.524 |
|
| 2nd repair size 93.072–93.060 |
2nd repair size 93.036–92.024 |
|
| D | nominal size 92.084–92.072 |
nominal size 92.048–92.036 |
| 1st repair size 92.584–92.572 |
1st repair size 92.548–92.536 |
|
| 2nd repair size 93.084–93.072 |
2nd repair size 93.048–92.036 |
* The 1st repair size is increased by 0.5 mm.
** The 2nd repair size is increased by 1.0 mm.
