4.4. Conrod and piston group

Pistons are manufactured of aluminum alloy, have the flat bottom and three flutes for rings.

On diameter pistons are broken into three groups for the nominal size and into two groups for the repair size (tab. 2.2).

Diameter of the piston, mm	Engine model
	GA14DE	GA16DE	SR20DE
1 - group of the nominal size	73,575-73,585	75,975-75,985	86,00-86,01
2nd group of the nominal size	73,585-73,595	75,985-75,995	86,01-86,02
3rd group of the nominal size	73,595-73,605	75,995-76,005	86,02-86,03
Repair group  - t-0,5	74,075-74,105	76,475-76,505	-
Repair   group +0,1	74,575-74,605	76,975-77,005	-
Repair   group +0,2	-	-	86,18-86,21

Dimensional groups are marked by figures on the piston bottom. Pistons of the repair sizes intend for installation in the block of cylinders after boring. The tag on the bottom of the piston has to be turned towards the drive of camshafts.

Diameter of an opening in lugs under a piston finger makes, mm:

for       GA 18,987—18,999 engines

for       SR 21,987—21,999 engines

The gap between a mirror of the cylinder and the piston makes, mm:

for       GA 0,015—0,035 engines

for       SR 0,01—0,03 engines

Piston fingers hollow, steel, tempered and polished, freely rotate in the plug of a rod and are pressed by small effort in a cold state in an opening of lugs of the piston. Fingers refrain from axial movement by two spring lock rings.

Diameter of a piston finger, mm:

       GF 18,989—19,001 engines

for       SR 21,989—22,001 engines

Tightness in an opening of a lug of the piston of 0 — 0,004 mm. A gap between a piston finger and the plug of the top head of a rod of 0,005 — 0,017 mm.

Fig. 2.4. Installation of piston rings: I \order of installation of piston rings; II \arrangement of locks of piston rings; 1 — the tag on the piston directed towards the drive of camshafts; 2 — a joint of a dilator of an oil scraper ring; 3 — the lock of the top compression and top oil scraper ring; 4 — the lock of an oil scraper ring; 5 — the lock of the lower compression ring

On each piston about three rings (fig. 2.4) are established: top compression chromeplated, with a barrel-shaped surface; lower compression scraper type; oil scraper with a dilator, top and lower rings.

The gap between piston rings and flutes of the piston makes:

— for the top ring — 0,04 — 0,08 mm, maximum permissible 0,2 mm;

— for the lower ring — 0,03 — 0,07 mm, maximum permissible 0,2 mm.

Gap in the lock:

— for the top ring — 0,2 — 0,35 mm;

maximum permissible for GA engines — 1 mm;

maximum permissible for SR engines — 0,49 mm;

— for the lower ring — 0,37 — 0,52 mm;

maximum permissible for GA engines — 1 mm;

maximum permissible for SR engines — 0,64 mm;

— for an oil scraper ring — 0,2 — 0,6 mm;

maximum permissible for GA engines — 1 mm;

maximum permissible for SR engines — 1,09 mm.

Rods steel, shod, double-T section, the lower head of a rod with the direct socket. At installation the tag on a cover of the lower head of a rod settles down opposite to a tag on a rod; the opening for lubricant is guided towards a starter.

The distance between centers of openings of the top and lower heads of a rod of GA engines makes 140,45 — 140,55 mm.

Diameter of an opening of the lower head of a rod, mm:

       GA 43,000—43,012 engines

       SR 51,000—51,013 engines

Diameter of an opening of the plug of the top head of a rod, mm:

       GA 19,000—19,012 engines

       SR 22,000—22,012 engines