This flange is the connection between the exhaust manifold and the exhaust riser. It bolts to the aft end of the engine with two studs. The easiest way, indeed sometimes the only way to replace an exhaust riser is to remove the exhaust flange from the manifold. Often the flange is so rusted it makes no sense to reinstall it.
This part is a more robust replacement for the earlier version which had too few threads for the riser. It is ridiculously expensive, but given that there were only 2,900 of these engines built, Westerbeke probably only casts 10 parts at a time. Since the last of the 5411's were built in 1982, we are tickled that Westerbeke even offers these parts any longer.
Applications include these engines (and the boats that we are aware used these engines... There could be other combinations as well):
• Universal 5411 raw water cooled (Catalina 27, Catalina 30)
• A new, thicker exhaust flange replacement
• Two new, longer studs to accommodate the thickness of the new flange
• Two special fine threaded nuts (Note that these are not shown in picture above)
• A new flange gasket
• Overall: 3-3/4" x 2-1/4" (not including mounting flange)
• Female thread: 1-1/4" NPT
• Studs: 3/8"
• Mounting hole spacing, center to center: 75mm (~3")
CAUTION: This part has been machined and then painted. There is some overspray in the fastener holes that will need to be cleared out to accept fastener screw.