If your pump was built after 2003, it is likely equipped with an "O" ring rather than a gasket. You will need kit #Z3645 for the Late Oberdorfer pump. You can find it listed below under "Required and Related Products"

You can identify this pump by referring to the drawing found below under the heading "More images". Note this impeller (#5) is accessed by removing a flat rectangular cover plate. The cover is secured to the pump body with four screws.

Sherwood and Oberdorfer pumps were used interchangeably until August 1986 when Medalist Universal Motors was acquired by Westerbeke.

This pump was used on the engines listed below (and the boats that we are aware used these engines... There could be other combinations as well):
• Atomic 4 w/ a replacement Oberdorfer pump (Catalina 30)
• M-12 (Catalina 25, Capri 26)
• M-2-12 (Catalina 25)
• 5411 (Catalina 27, Catalina 30)
• M-18 (Catalina 27, Catalina 30)
• M-25 (Catalina 30)
• M-25XP (Catalina 28, Catalina 30, Catalina 34, Catalina 36)
• M3-20 (Catalina 27, Catalina 28, Catalina 30)
• M-35 (Catalina 34, Catalina 36, Catalina 38)
• M-50 (Catalina 42)

• Outside diameter (of a new impeller): 2"
• Width: 7/8"
• Inside diameter: 1/2"
• Number of blades: 6

1) This pump may have been replaced with the late model Sherwood pump by a previous owner. Earlier Universal diesel engines of most any model could have the newer pump as Universal provides an upgrade kit to replace older Sherwood or Oberdorfer pumps that have worn out. Compare your pump to the drawing to ensure you are ordering the correct impeller kit. If your pump doesn't look like this drawing, see the pump below under "Required and Related Products" for the late Sherwood replacement pump impeller.

2) In 2004 Oberdorfer changed the seal on the cover plate from a paper gasket to a reusable "O" ring. The paper gasket included in this kit will not be used on a pump equipped with an "O" ring seal. If you have a later pump with an "O" ring seal, use our part number Z3645 that includes the impeller and the newer "O" ring.

3) At about the same time as the gasket change, Oberdorfer changed another characteristic that will help you to determine if you have the paper gasket or the "O" ring before you open the pump. Order the proper parts in advance before you need them. In early pumps the cam inside which flexes the impeller vanes (and causes the pump to pump) was a separate piece. In later pumps the cam was machined as an integral part of the casting. The machine screw that secures the cam into the early pump is visible on the outside of the pump body, between the two ports. Since the later pumps don't have the separate cam, there is no machine screw visible. So, if you pump was built around 2004, check for the head of this machine screw. If it has the screw you likely have a paper gasket. If there is no machine screw you likely have the "O" ring seal.