MG Car Repair: MGA oil pressure, water temp gauge, hexagon nut

Question
Hi Howard, I would like to know how the MGA measures its oil pressure.  I am having a difficult time, because my MGA is missing a number of parts; I have the combination oil pressure/water temp gauge, and the pipe that connects to the back of the gauge.  I see no sender unit on the engine, but just a small male end pipe threaded fitting in the middle of a hexagon nut.  The MGA repair manual is not particularly illustrative.  The Moss Motors catalog shows a flexible pipe that seems to connect to the pipe I have: does that flexible pipe (in the catalog) connect directly to that fitting on the engine I described?  

Thank you in advance for any and all information you can give me.

Regards,
Dan

Answer
Hi Dan,

The MGA has a hydraulic operated gauge (half gauge). It uses oil from the engine block pumped from a fitting on the block and oil is pumped through a small diameter pipe to the gauge itself. When the engine is running it pumps oil to the galleys and to the bearings and also to other parts that need oil. Because the bearings are tight the oil can not get much past the bearings (when they are good) then the pump builds up pressure and it would continue to build until something exploded and the weakest place is usually the oil filter or the part of gauge line that is a flexable hose. However in the engine block there is a pressure regualtor valve that opens and controls the high pressure and keeps it down.

If the bearings in the engine are badly worn then the oil can flow through them and little pressure is built up. An engine with good bearings will restrick the oil and allow the pressure to build. At idle (750 to 900 RPM) the oil pressure should be from 25 PSI to 50 PSI with proper oil and warm. At 2000 RPM and higher it should read from 45 PSI on up to 70 PSI. (depending on the temperature and weight of oil)

The pipes and fittings should be available from Moss Motors, Victoria British, Engel Imports, The Roadster Factory or British Parts Northwest. There are others but those are suppliers I have had dealings with and I know they are good. Most of them have toll free numbers to call.

Howard