11 25 530 Removing and installing or replacing all pistons (M52 / S52 / M52TU / M54 / M56): Installation:

Installation of pistons is described separately from removal. The assembly sequence differs between removal and installation.

The piston pin must be able to be pressed through the liner by hand with little force and must not display any significant play.

Fig 1: Installing Piston Pin

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Measure piston installation clearance:

Measure piston diameter with micrometer at distance A from the underside of the piston and at offset angle of 90° to piston pin axis.

Fig 2: Measuring Piston Diameter With Micrometer

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Measurement A, refer to ENGINE - TECHNICAL DATA .

Adjust micrometer to cylinder bore of engine block, set internal caliper on micrometer to zero. Measure bottom, center and top of cylinder bore in direction of travel and direction of engine rotation.

Fig 3: Adjusting Micrometer To Cylinder Bore Of Engine Block

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Diameter of cylinder bore, refer to ENGINE - TECHNICAL DATA .

Piston installation clearance, refer to ENGINE - TECHNICAL DATA .

Total permissible wear tolerance, refer to ENGINE - TECHNICAL DATA .

Replace connecting rod bearing shells. Refer to 11 24 571 REPLACING ALL CONNECTING ROD BEARINGS (M52 / S52 / M52TU / M54 / M56) .

Fit connecting rod with piston pin to piston in such a way that both of the visible pair numbers on the installation direction arrow on the piston point to the right.

Fig 4: Fitting Connecting Rod With Piston Pin To Piston

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Install snap ring so that opening is opposite recess.

Fig 5: Installing Snap Ring

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Insert special tool 11 2 470 in connecting rod.

Fig 6: Inserting Special Tool In Connecting Rod

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Lightly coat pistons and piston rings with oil.

Align contact points on piston rings (offset at approx. 120°, but do not arrange over piston pin lug).

Piston diameter 80 mm:

Press together piston rings with special tool 11 2 260.

Fig 7: Pressing Together Piston Rings With Special Tool

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Install piston so that arrow points to camshaft drive.

Fig 8: Installing Piston Using Special Tool

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Entire circumference of tightening strap must rest firmly on engine block.

Press in piston only with finger force (do not knock in!).

Attach crankpin to connecting rod.

Fig 9: Attaching Crankpin To Connecting Rod

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Apply light coat of oil to connecting -rod bearing shells. Fit bearing caps so that pair numbers match up. Install new connecting rod bolts.

Fig 10: Fitting Bearing Caps

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Tighten down connecting rod bolts with special tool 00 9 120 or special tool 11 2 110.

Fig 11: Tightening Down Connecting Rod Bolts With Special Tool

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Tightening torque 11 24 1AZ. Refer to ENGINE - TIGHTENING TORQUES .

Install oil pump. Refer to 11 41 000 REMOVING AND INSTALLING/REPLACING OIL PUMP (M52TU / M54 / M56) .

If oil pump and oil scraper are two parts:

Fit oil scraper.

Fig 12: Fitting Oil Scraper

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Assemble engine.