Design and specification of the crank mechanism (Mercedes-Benz E-Class W123)

Pistons

Aluminum alloy piston with flat bottom.

The piston bottom is marked with a piston diameter mark and an arrow for orienting the piston when installing it in the cylinder, which should be directed towards the camshaft drive. The pistons of one engine should not differ from each other by more than 4.9 g in weight.

Characteristic	Meaning
Clearance between piston and cylinder, mm
nominal
M 102	0,016—0,040
for other models	0,025—0,035
maximum permissible in operation	0,10

Piston diameter *

Parameter, mm	Engine model
Parameter, mm	M 115.938	M 102.920, M 102.939	M 102.980, M 102.982	M 115.954
nominal
class 1	86,98	88,968—88,982	95,468—95,482	93,73
class 2	—	88,978—88,992	95,478—95,492	—
class 3	—	88,988—89,002	95,488—95,502
1st repair size
class 1	87,48	89,468—89,482	95,968—95,982	94,13
class 2	—	89,478—89,492	95,978—95,992	—
class 3	—	89,488—89,502	96,988—96,002	—
2nd repair size
class 1	87,98	89,968—89,982	96,468—96,482	94,53
class 2	—	89,978—89,992	96,478—96,492	—
class 3	—	89,988—90,002	96,488—96,502	—
3rd repair size
class 1	88,48	—	—	—
Parameter, mm	M 123.920, M 123.921	M 110.923	M 110.984, M 110.988
nominal
class 1	85,98	85,98
class 2	—	—
class 3	—	—
1st repair size
class 1	86,48	86,48
class 2	—	—
class 3	—	—
2nd repair size
class 1	86,98	86,98
class 2	—	—
class 3	—	—
3rd repair size
class 1	—	—

* The difference in values is due to the model year of production.

Piston pins

The piston pin is steel, ground, floating. The pin is held from axial displacement by retaining rings.

Piston pin characteristics

Parameter, mm	Engine model
	M 102.920, M 102.939	M 102.980, M 102.982
Diameter
outer	23,995—24,000
interior	15,5
Length	—
Clearance between the pin and the bushing of the upper connecting rod head	0,007—0,02
Clearance between the pin and the piston boss	0,002—0,012

Piston rings

Three grooves are machined on the outer surface of the piston for installing rings. Assembly position: the "Top" mark should be facing upwards. On M 102 engines, piston rings from "Goёtze" or TRW can be installed.

Design features of "Goötze" piston rings

The upper compression ring is cylindrical, with a chamfer on the inner surface, with a porous chrome plating of the outer surface. The lower compression ring is conical, with a flange. The oil scraper ring has two chamfers, a retractable coil spring and a chrome-plated outer surface.

Design Features of TRW Piston Rings

The upper compression ring is cylindrical, with a chamfer on the inner surface, with a chrome-plated ground barrel-shaped outer surface. The lower compression ring is conical, with a flange and a barrel-shaped chrome-plated outer surface. The oil scraper ring has two chamfers, with a coiled expansion spring and a chrome-plated outer surface.

Characteristics of piston rings

Parameter, mm	Engine model
	M 115.938	M 102.920, M 102.939	M 102.980, M 102.982	M 115.954
Height clearance
upper compression ring	0,05—0,08	0,05—0,085	0,050—0,085
lower compression ring	0,03—0,06	0,01—0,03	0,03—0,06
oil scraper ring	0,01—0,04	0,01—0,045	0,01—0,04
Maximum height clearance in operation
upper compression ring	0,15
lower compression ring	0,10
oil scraper ring	0,16	0,10		0,16
Gap in the lock
upper compression ring	0,30—0,55
lower compression ring	0,25—0,45
oil scraper ring	0,25—0,50
Maximum clearance in the lock in operation
upper compression ring	1,0	1,0		1,0
lower compression ring	0,8	0,8		0,8
oil scraper ring	0,8	0,8		0,8
Parameter, mm	M 123.920, M 123.921	M 110.923	M 110.984, M 110.988
Height clearance
upper compression ring	0,050—0,085
lower compression ring	0,03—0,06
oil scraper ring	0,01—0,04
Maximum height clearance in operation
upper compression ring	0,15
lower compression ring	0,10
oil scraper ring	0,16
Gap in the lock
upper compression ring	0,30—0,55
lower compression ring	0,25—0,45
oil scraper ring	0,25—0,50
Maximum clearance in the lock in operation
upper compression ring	1,0
lower compression ring	0,8
oil scraper ring	0,8

Connecting rods

The connecting rod is an I-section steel, forged with replaceable liners. The lower connecting rod head cover is of straight section. A hole is drilled in the connecting rod rod to supply oil to the rubbing surfaces. The connecting rods of one engine should not differ from each other by more than 5 g in weight.

Characteristic	Meaning
Non-parallelism and non-flatness of head holes when measured at a distance of axes of 100 mm from the connecting rod, no more than, mm
M 102	0,045
M 115	0,030
M 110	0,040
M 123	0,040
Surface roughness of the piston-to-connecting rod joint, µm	0,002
Runout of the holes of the lower head of the connecting rod, not more than, mm	0,02

Connecting rod characteristics

Parameter, mm	Engine model
Parameter, mm	M 115.938	M 102.920, M 102.939	M 102.980, M 102.982	M 115.954
Connecting rod lower head diameter	55,60—55,62	51,60—51,619		55,60—55,62
Connecting rod upper head diameter	29,00—29,02	27,00—27,021		29,00—29,02
Inner diameter of the upper head bushing	26,012—26,018	24,007—24,015		26,012—26,018
Distance between the axes of the head holes	148,95—149,05	144,95—145,05		148,95—149,05
Width of the lower head	32.08—32,10	27,857—27,90		32.08—32.10
Parameter, mm	M 123.920, M 123.921	M 110.923	M 110.984, M 110.988
Connecting rod lower head diameter	51,60—51,62
Connecting rod upper head diameter	26,00—26,02
Inner diameter of the upper head bushing	23,007—23,013
Distance between the axes of the head holes	130,95—131,05
Width of the lower head	27,86—27,89

Connecting rod cap bolts

Pull-out bolts.

Characteristic	Meaning
Thread diameter	M9x1
Rod diameter, mm
M 102
new bolts	8,3—8,4
maximum permissible	8,0
M 115
new bolts	8,3—8,4
maximum permissible	8,0
M 110
new bolts	7,3—7,4
maximum permissible	7,1
M 123
new bolts	7,3—7,4
maximum permissible	7,1
Height of bolt head (M 102), mm	5,0—5,2
Length of threaded part (M 102), mm	40,0
Length to head (M 102), mm	51,7—52,0

Crankshaft

Crankshaft steel, forged four- (engine M 123), five- (engines M 102, M 115) or semi-supportive (engine M 110).

Crankshaft of 4-cylinder engines (M 102, M 115) has eight counterweights, 6-cylinder (M 110, M 123) - 12 counterweights.

Characteristic	Meaning
Permissible end runout of main bearing cheeks, mm	0,02
Radii of fillets of main and connecting rod journals, mm	2,5—3,0
Front end diameter of crankshaft, mm	29,987—30,000
Permissible runout of the front end of the crankshaft, mm	0,030
Rear oil seal bearing surface diameter, mm	92,874—92,928
Flange non-cylindricality, up to, mm	0,02
Flange runout, up to, mm	0,012
Runout of main journals (the crankshaft is mounted on the prisms of journals 1 and 5), up to, mm
necks 2 and 4	0,07
necks 3	0.10

Crankshaft clearances for engine M 102

Characteristic	Meaning
Diametrical clearance between main journal and bearings, mm
nominal	0,025—0,045
wear limit in operation	0,070
Diametrical clearance between the crankpin and the bearings, mm
nominal	0,030—0,050
wear limit in operation	0,070
Crankshaft axial clearance, mm
nominal	0,06—0,22
wear limit in operation	0,30
Axial clearance between connecting rod and crankshaft, mm
nominal	0,11—0,23
wear limit in operation	0,50
Permissible ovality of main and connecting rod journals in operation, mm	0,025
Permissible taper in operation, mm
connecting rod journals	0,010
root necks	0,015
Permissible imbalance of the crankshaft in operation, g.cm	15

Crankshaft parameters

Parameter, mm	Engine model
	M 115.938	M 102.920, M 102.939	M 102.980, M 102.982	M 115.954
Main journal diameter
nominal
1st grade	69,95—69,96	57,935—57,940		69,95—69,96
2nd grade	*	57,940—57,945		*
3rd grade	*	57,945—57,950		*
4th grade	*	57,950—57,955		*
5th grade	*	57,955—57,960		*
6th grade	*	57,960—57,965		*
1st repair size	69,70—69,71	57,705—57,715		69,70—69,71
2nd repair size	69,45—69,46	57,455—57,465		69,45—69,46
3rd repair size	69,20—69,21	57,205—57,215		69,20—69,21
4th repair size	68,95—68,96	57,955—57,965		68,95—68,96
Width of main journals
nominal	34,00—34,03	28,500-28,521 or 28,600-28,621		34,00—34,03
1st repair size	34,00—34,03	28,700—28,721		34,00—34,03
2nd repair size	up to 34.60	28,900—28,921		up to 34.60
3rd repair size	up to 34.60	29,000—29,021		up to 34.60
4th repair size	up to 34.60	*		up to 34.60
Distance between supporting surfaces of thrust half rings
	—	23,979—24,000		—
Diameter of connecting rod journals
nominal	51,97—51,96	47,955—47,965		51,97—51,96
1st repair size	51,70—51,71	47,705—47,715		51,70—51,71
2nd repair size	51,45—51,46	47,455—47,465		51,45—51,46
3rd repair size	51,20—51,21	47,205—47,215		51,20—51,21
4th repair size	50,95—50,96	46,955—46,965		50,95—50,96
Width of connecting rod journals
nominal	32,0—32,1	27,000—28,034		32,0—32,1
repair size	up to 32.30	until 28.30		up to 32.30
Parameter, mm	M 123.920, M 123.921	M 110.923	M 110.984, M 110.988
Main journal diameter
nominal
1st grade	59,95—59,96
2nd grade	*
3rd grade	*
4th grade	*
5th grade	*
6th grade	*
1st repair size	59,70—59,71
2nd repair size	59,45—59,46
3rd repair size	59,20—59,21
4th repair size	58,95—58,96
Width of main journals
nominal	29,00—29,02
1st repair size	29,00—29,02
2nd repair size	up to 29.60
3rd repair size	up to 29.60
4th repair size	up to 29.60
Distance between supporting surfaces of thrust half rings
	—	—	—
Diameter of connecting rod journals
nominal	47,95—47,96
1st repair size	47,70—47,71
2nd repair size	47,45—47,46
3rd repair size	47,20—47,21
4th repair size	46,95—46,96
Width of connecting rod journals
nominal	28,00—28,08
repair size	until 28.30

Main and connecting rod bearing shells

Bearing shell marking color: blue or gray.

Characteristic	Meaning
Width of inserts, mm
Engines M 102 and M 115
nominal	33,80—33,90
repair	34,40—34,60
Engines M 110 and M 123
nominal	28,78—28,90
repair	29,40—29,60

The liners for all repair stages are supplied with excess width and must be reworked to fit the reground bearing.

Engines of the M 102 models produced since July 1986 have the thickness of the main bearing shells increased by 0.003 mm in order to reduce the gap and reduce noise during engine operation.

Characteristics of main and connecting rod bearing shells

Parameter, mm	Engine model
	M 115.938	M 102.920, M 102.939	M 102.980, M 102.982	M 115.954
Main bearing shell thickness
nominal	2,25	2,25		2,25
1st repair size	2,37	2,37		2,37
2nd repair size	2,50	2,50		2,50
3rd repair size	2,62	2,62		2,62
4th repair size	2,75	2,75		2,75
Connecting rod bearing shell thickness
nominal	1,80			1,80
1st repair size	1,92			1,92
2nd repair size	2,05			2,05
3rd repair size	2,17	2,18		2,17
4th repair size	2,30			2,30
Parameter, mm	M 123.920, M 123.921	M 110.923	M 110.984, M 110.988
Main bearing shell thickness
nominal	3,50
1st repair size	3,63
2nd repair size	3,75
3rd repair size	3,88
4th repair size	4,00
Connecting rod bearing shell thickness
nominal	1,81
1st repair size	1,93
2nd repair size	2,06
3rd repair size	2,18
4th repair size	2,31

Engine flywheel M 102

The flywheel is secured with eight bolts. The mounting hole is opposite the drilling in the crankshaft.

Characteristic	Meaning
Diameter of the centering collar of the crown, mm	275,31—275,39
Distance between the working surface of the driven disk and the supporting surface of the clutch housing, mm	22,5—22,6
Distance between the working surface of the driven disk and the head of the flywheel mounting bolt, mm
nominal	16,6
after grinding, not less than	15,5
Non-flatness of the working surface of the driven clutch disc, no more than, mm	0,05
Outer diameter of the working surface of the driven clutch disc, mm	222,0
Outer diameter of the bearing surface of the clutch housing, mm	253,0
Flywheel mounting compensation bolt rod diameter, mm
for new bolts	8,5
minimum	8,0
Bolt length to head, mm
for new bolts	22±0,2
maximum	22,5