The
oil pressure gauge, along with all the others, is a Kirkham/Speedhut unit.
I've dropped the
oil pan and taken off the
oil pump. The pressure relief plunger initially felt as though it was jammed, but it moved freely enough now after spraying some cleaner in there and working it up and down a few times.
However, for the price of a new 57HV pump, I'm tempted to just fit a new one.
There was nothing inside the oil pan that wasn't supposed to be there, so I'm reasonably happy that there isn't something seriously amiss elsewhere in the engine.
Many thanks for the input and advice.
Paul