300SL Fuel Injection Pumps
Housing Comparison
UNDERSTANDING ThE EVOLUTION OF THE 300SL FUEL INJECTION PUMP HOUSING
Though similar at first glance, there are many differences between the R2, R3, and R8 fuel injection pumps produced for the W198 300SL that led to improved performance and better calibration. In the following images and paragraphs we will outline these changes, explain how they effect the operation of the pumps, and show the gradual evolution which eventually resulted in the W113 pumps including the R11 and beyond.
The PES6KL 70/320 R2 is a pneumatic governor pump built for the W198 300SL and features the inline setup that would be used for Mercedes-Benz vehicles moving forward. Main differences from later pumps are a smaller viewing port, roller tappet guide screws below the viewing port on the front side of the housing, location of the fuel feed pump, and locating pins above the viewing port.
PES6KL 70/320 R2
The main differences between the PES6KL 70/320 R2 and R3 are the location of the fuel feed pump and roller tappet guide screws and an asymmetrical bottom screw orientation. The guide screws shifted to the rear-side of the pump allowing the movement of the fuel feed pump, noticeable due to the elongated shape left over and the asymmetrical bottom plate. This change allowed the fuel feed pump to use an existing camshaft lobe whereas the R2 feed pump required its own as it didn't line up appropriately with the existing lobes.
PES6KL 70/320 R3
PES6KL 70/320 R8
The PES6KL 70/320 R8 is the last pump used in the W198 300SL and bears many hallmarks of later pumps such as the PES6KL 70/120 R11. Differences on the frontside include the elimination of the elongated shape around the fuel feed pump and removal of the fuel inlet and fuel bleeder. The locating pins have shifted to the rear, and there is also an additional screw hole at the bottom-rear which is for the oil feed line securing bracket.
Camshafts
PES6KL 70/320 R2
PES6KL 70/320 R3 & PES6KL 70/320 R8
Bottom Plates
Here you can see the camshaft from the R2 in comparison to that found in the R3 and R8. The R2 features an additional lobe for the fuel feed pump in between the fourth and fifth lobes. This is due to the placement of the fuel feed pump which did not line up with either fourth or fifth lobes. When the roller tappet guide screws were moved to the back on the R3 the fuel feed pump could shift right and use the fifth lobe rather than requiring its own. This simplified manufacturing saving time and money.
PES6KL 70/320 R2
PES6KL 70/320 R3
As a result of the shifting fuel feed pump location, one screw on the bottom plate had to be moved, resulting in the asymmetrical layout seen here. The elongated shape around the screw hole remains on the R3 but was removed on the R8. They also added additional bracing to the underside of the plate for increased strength.
The cavities seen in the bottom plates actually come from an earlier design; felt pads which lightly rubbed the camshaft lobes were seated in these circular spaces. These pads are not present in later pumps, though the spaces remain.
PES6KL 70/320 R8
Camshaft Bearing Covers
PES6KL 70/320 R2
PES6KL 70/320 R3 & PES6KL 70/320 R8
Another difference between pump models can be found in the camshaft bearing cover. The R2 and early R3s used an aluminum cover while later R3s and the R8 used steel. The steel models also featured two notches to help in removal. A flat screwdriver can be inserted into the gap and used to pry the plate off the housing for easier disassembly. Previously a special tool had to be used to push the plate out from the other side of the pump housing.
