Service Bulletin: Oil Pressure Relief Valve
Triumph service bulletin dated 6-6-1973
Today's blog post is on a Triumph service bulletin dated June 6, 1973. This brief service bulletin describes the fine screen and coarse screen oil pressure relief valves used on twins and triples. Now your probably thinking to yourself why is this important? Aren't all oil pressure relief valves the same? According to Triumph some are not the same. We will also cover more information that this service bulletin does not include.
What is an oil pressure relief valve?
Oil pressure relief valves are fitted to most vintage British (if not all) motorcycles to discharge excess oil pressure when the engine is cold. When an engine is cold oil is typically thicker causing pressure to build up in the crankcase. The oil pressure relief valve relives additional pressure and re-routes the oil to a separate passage until the oil warms and thins thus lowering pressure.
Are all oil pressure relief valves the same?
Yes to a certain extent. I use the word interchangeable cautiously because most oil pressure relief valves look the same but internally some are different to accommodate certain models and engine sizes. It is important to use the correct oil pressure relief valve for your specific application.
The fine screen oil pressure relief valves where typically fitted to Triumph and BSA twins. Almost all reproduction oil pressure relief valves on the market today have the fine screen for both twins and triples. The best way to ensure a part is correct for your application is to check the screen but to also check the internal spring by removing the top cap. Most workshop manuals will list the proper spring length for each application.