Removal and installation of piston

03—316 Removal and installation of piston

Association piston — cylinder¹ )

The smallest measured cylinder dia and the largest measured piston dia are decisive for association.

Engine

Normal compression

110.921 110.922 110.923 110.924 110.981 110.982

110.983 110.984 110.985 110.986 110.987

Std

37, 40, 50, 60, 64, 69 80M.83, 86′),89

Standback 0.20 to 0.70

9.0±0.2 8.7 ±0.2

+ 0.5

38,  41, 51, 67, 70, 84,90

39,  42, 52, 68, 71, 85, 91

Standback 1.0 to 1.50

+ 1.0

Low compression

8.0-0.4

0.25 standout up to 0.15 standback

Standback 0.55 to 0.95

¹ ) Installed in engine 110.984, 110.985, 110.986 and 110.987 as standard equipment. Not available as repair stages. Use only together with piston of same piston code number.

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New                                Wear limit

(Installation tolerance)

Piston pin clearance

in conrod bushing

0.007 to 0.017

in piston

0.002 to 0.011

Piston ring gap

groove 1 groove 2 groove 3

0.30 to 0.45 0.30 to 0.45 0.25 to 0.40

1.0 0.8 0.8

Piston ring clearance

groove 1 groove 2 groove 3

0.05 to 0.08 0.03 to 0.06 0.01 to 0.04

0.15 0.08 0.08

Connecting rod nuts

torque pressure

40-50 Nm

torque angle

90-100°

Piston ring pliers

000 589 51 37 00

Piston ring compressor

000 589 04 14 00

The piston version (std, + 0.5 or + 1.0), the group number (0, 1 or 2), the piston code (e.g. 40) and an arrow for forward direction are stamped in the piston crown.

The

group number is also stamped in the crankcase

mating surface.

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The group number of pistons (e.g. 1) is the same as the group number of cylinder bores (production).

This will guarantee the specified piston clearance.

When repairing, the cylinder bores should be honed according to the sizes of the existing pistons plus the piston clearance.

Pistons and piston pins are matched.

The measuring point for nominal diameter of pistons is offset by 90° in relation to piston pin axis at level H.

On used pistons the measured value does not necessarily correspond with nominal diameter of a new piston, since piston in range of measuring point and at shaft tab may “recede” already after a short operating period, that is, the nominal diameter may become smaller by up to 0.070 mm.

Piston normal compression dimension H = 32 mm

If used pistons are used again, make sure that the oil drain bores in 3rd piston ring groove are cleaned.

Piston low compression and USA version dimension H = 32 mm

1 Take out connecting rod with piston from above.

2 Remove piston pin circlips and press out piston pin.

3 Repair and square connecting rod (03—313).

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4 Place piston on connecting rod that arrow (1) faces in forward direction and circlip grooves (2) in connecting rod face to left side of engine (intake manifold).

Don’t heat piston.

5 Press in piston pin coated with engine oil by hand.

6   Insert piston pin circlips in grooves.

When installing used pistons, check piston ring gaps and clearances.

Check piston rings for easy movement.

7   Lubricate cleaned cylinder bores, conrod bearing journals, conrod bearing shells and the pistons.

8   Distribute gaps of piston rings around piston circumference evenly.

9   Install piston ring compressor and guide in piston with arrow facing forward.

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10   Place connecting rod bearing caps with code numbers facing each other on connecting rod and tighten connecting nuts to 40—50 Nm initial torque and to 90—100° angle of rotation torque.

11    Turn crankshaft and check clearance between piston pin boss and connecting rod.

12   Measure distance between piston crown and crankcase mating surface when piston is positioned at TDC (see chart).

1   Plain compression ring

2   Oil scraper ring

3   Bevelled compression ring with hose lined spring

4  Piston

5   P’ston, USA and low compression

6   Circlip

7   Connecting rod with conrod cap

8   Conrod bolt

9   Nut

10  Conrod bushing

11   Conrod pin

12   Conrod bearing upper half with oil bore

13  Conrod bearing lower half

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