Modifications to the pistons - ra03006010317x(0317)

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Engines 601, 602 (except 602.98), 603

Piston pin bearings Engines 601, 602 and 603

Since 08/85 piston pin bore provided with angular oil pockets (previously flat oil pockets) for improved lubrication.

Engines 601.91, 602.91, 603.91

The piston skirt has been provided with a larger recess (arrow) for better clearance on engines with oil injection nozzles or exhaust gas recirculation.

Standardization with engine 601.91 .

Piston code: 15.

Fig 1: Locating Piston Skirt With Larger Recess

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Each piston is equipped with two compression rings and one oil scraper ring.

The first piston ring groove is provided with a Niresit ring carrier.

Fig 2: Identifying Piston Pin Thickness

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Engines 601.91, 602.91, 601.91 as of 09/89

The height of the ring groove for the rectangular ring (180) has been increased from 2.0 to 2.5 mm.

Piston code 16 (Mahle co.)

Piston code 17 (Alcan co.)

Fig 3: Identifying Height Of Ring Groove

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

These pistons can also be installed in engines with cylinder sleeves.

Engines 601.91, 602.91 and 603.91

In 03/88 temporary installation of pistons from

Alcan, piston code 12,

KS, piston code 14

Engines 602.961, 603.96/97 as of 12/87 (turbo)

Piston pins

The size of the piston pin has been increased to reduce the surface pressure.

Fig 4: Identifying Piston Pin Dimension

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Engines 602.961, 603.96

Pistons with annular gallery

Due to the higher thermal load the pistons are cooled with oil via an annular gallery in the piston crown. Moreover the piston pins are supplied with oil injected through the two bores (2.0 mm dia., arrows), ending in the annular gallery.

The required oil is supplied via injection nozzles located in the crankcase on the right side.

Fig 5: Locating Pistons With Annular Gallery

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Engine 603.970/971 up to 03/95

The annular gallery is not fitted in these engines. Oil is supplied only to the piston crown.

Fig 6: Identifying Piston Annular Gallery

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

A recess is located on the piston skirt (arrow) for the oil injection nozzle.

The precombustion chamber recess in the piston crown has a diameter of 18 mm (normally aspirated engine = 17 mm).

Fig 7: Locating Piston Skirt

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Engine 603.970/971 as of 09/95

Pistons with semi-cooling gallery for cooling pistons and modified piston rings.

This piston must be installed only as a set as it is 5 g heavier than its predecessor.

Piston code: 18

Fig 8: Identifying Piston With Semi-Cooling Gallery

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Piston crown

On engines 602.96 and 603.97 from the start of production and on engine 603.96 starting 08/88 moose horn recess pistons are installed (previously star recessed pistons).

The piston crown is coated with aluminum oxide on both piston versions.

Fig 9: Identifying Moose Horn Piston

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 10: Identifying Star Recessed Piston

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

These pistons each have two compression rings and one oil scraper ring. The piston skirt is graphitized.

Piston codes:	00 Engine 602.96
	13 Engine 603.96

Fig 11: Identifying Compression Rings Dimension

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Motoren 601.91, 602.91, 603.91 ab 01/91

In these motors, pistons with graphited piston shaft are incorporated.

Kennzahl 22.

Engine 602.982

Piston with bowl and annular gallery for cooling piston (arrow). Piston stem graphited.

Piston code: 06

Fig 12: Locating Piston Cross Section View With Bowl And Annular Gallery

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 13: Locating Travel Piston Code

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Oil spray nozzle for cooling piston made of sheet steel, interference-fitted in crankcase.

The oil is distributed along an annular gallery drilling and flows back into the sump. As the oil flows through the annular gallery, it absorbs heat and thus cools the piston crown.

Opening pressure: 1.5 bar

Fig 14: Identifying Oil Spray Nozzle For Cooling Piston

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.