1, 2 - compression ring; 3 - oil scraper ring; 4 - piston; 5 - piston pin; in - retaining ring (∅22x1,5); 7 - bushing of the upper head; 8 - connecting rod; 9 - centering sleeve; 10 - insert (blue); 11 - insert (red); 12 - connecting rod cover; 13 - connecting rod bolt (47 mm)
Piston
Pistons installed on the engine (pic. 3.12,a) firms «Mahle» made of aluminum alloy with steel inserts.
Each piston has two compression rings and one oil scraper ring. For the correct orientation of the piston when installed in the cylinder, there is an arrow on its bottom, which must be turned towards the camshaft drive, as well as a mark indicating its diameter. The piston diameter is measured at a distance of 8 mm from the lower edge of the piston skirt at an angle of 90°relative to the axis of the piston pin.
B22 | B25/B30 | |
Piston diameter, mm | ||
nominal | 79,980 | 83.995 |
intermediate | 79,993 | 84.009 |
1st repair size | 80,230— 80,243 | 84,235— 84,259 |
Estimated clearance between piston and cylinder for new parts | from 0.01 to +0.04 | |
Max. valid. | 0,15 | |
Permissible difference in weight between pistons for one engine, g. | 10,0 |
Piston pins
piston pin (pic. 3.12.5) steel, polished, floating type.
From axial movement, it is held by two retaining rings in the piston holes for the piston pin. Fingers are made in two classes, marked with colored marks - black and white.
The piston pin diameter of the engine is 22 mm, with a manufacturing tolerance of -0.003 to -0.006 mm.
The nominal clearance between the piston pin and the piston is 0.001-0.005 mm. Clearance between piston pin and connecting rod bushing:
- fingers with «white» label - 0.005-0.013 mm;
- fingers with «black» label - 0.008-0.015 mm.
Piston rings
Piston rings are installed in the grooves of the piston head: two compression (1,2) and one - oil scraper (3).
Rings are installed on the piston with a mark «Thor» («Top») to the bottom of the piston (fire belt). The upper compression ring is chrome-plated, with rounded edges, the lower compression ring is tapered, the oil scraper ring with expander.
Gap between new piston ring and groove wall:
- upper compression 0.020-0.060 mm;
- lower compression 0.020-0.060 mm;
- oil scraper 0.020-0.060 mm;
- maximum allowable 0.12 mm.
Gap in breaking a new piston ring:
- upper compression 0.10-0.30 mm;
- lower compression 0.20-0.40 mm;
- oil scraper 0.20-0.60 mm.
The maximum allowable gap in the lock for all engine models for compression rings is 0.80 mm, oil scraper rings 1.00 mm.
Connecting rods
connecting rods (8. fig. 3.12b) forged, with H-shank made of heat-treated steel, with thin-walled tri-metal inserts (10, 11) plain bearings.
A bimetallic, convoluted rod is pressed into the upper head of the connecting rod (rolled up) sleeve (7).
According to the diameter of the hole of the lower head, the connecting rods are divided into two size groups, marked with color marks in red and blue.
Connecting rod bore diameter:
- with a red mark 48.000-48.008 mm;
- with a blue mark 48.009-48.016 mm.
The lower head of the connecting rod is finished with its cover (12) and is not subject to further dismantling.
Connecting Rod Bushing Diameter:
- outer 24.060—24.100 mm;
- internal 22.011—22.005 mm;
The diameter of the lower head of the connecting rod, without bearing 48.000-48.016 mm.
The maximum permissible operating clearance between the connecting rod bearings and the crankshaft journals for all engine models is 0.12 mm. Permissible difference in weight between connecting rods on one engine, no more than 4.0 g.
Permissible twisting of the connecting rod for all engine models is no more than 30'. The tolerance of non-parallelism and misalignment of the axes of the holes over a length of 100 mm, for all engine models, is not more than 0.04 mm. The maximum axial clearance of the connecting rod on the neck of the crankshaft relative to its cheek for all engine models is not more than 0.37 mm.