1/1/2006
Tech Notes
Oversize piston and revised bore specification for 1999-2004 Subaru 2.5L SOHC engines
Engine Builders: The AERA Technical Committee offers the following information regarding an oversize piston and revised bore specification for 1999-2004 Subaru 2.5L SOHC engines. This engine uses a selective bore process for determining piston use.
Originally, the pistons selected were either an "A" or "B" to obtain the desired 0.010 - 0.030 (mm) piston to wall oil clearance. Note that the Standard "B" piston is smaller in diameter when compared to the others listed in Chart 1.
Chart 1, Figure 1, Chart 2
To repair slightly damaged bores, the engine manufacturer has recently released "A" and "B" 0.061 (mm) oversize pistons as shown in Chart 2. Part numbers for these oversize pistons are shown in that chart as well.
Engine Builders: The AERA Technical Committee offers the following information regarding a polymer - plastic oil pump screen replacement for 2001 Ford 4.0L VIN E engines. This bulletin applies to engines built before March 2001.
Some Ford Sport truck 4.0L V6 engines built before March 2001 use polymer-plastic oil pump pickup screen assemblies. This polymer-plastic oil pump pickup screen assembly has failed in some engines and can easily break. In April 2001, Ford changed the assembly to a steel oil pump pickup screen design to reduce potential problems in this area of the engine. They again modified it in subsequent years to make replacing and interchanging components difficult.
Most engine builders prefer a metal component as opposed to plastic component inside their engines, as metal is obviously more durable. You can replace the early style polymer-plastic oil pump pickup screen with the later steel assembly, but you will need a special 90° adaptor (p/n F77Z6622BA) that is currently sold only by Ford. The 90° adaptor allows you to connect the oil pump to the oil pickup screen.
Aftermarket cataloging may not show all the different combinations used but engine builders report using an M128 oil pump, F77Z6622BA adaptor and 300S pickup screen, to make a successful repair.