Oil pressure gauge thread
Smiths gauges use a 1/8" BSP thread (but some people think it is 1/8" NPT ??)
Oil pressure warning lamp
"Yesterday my oil light started to come when the car was
ticking over, today it stays on in every gear until just before I change. Should
I change the oil quickly?"
You engine isn't developing enough oil pressure, or the warning system is
faulty.
Stuck open relief valve
Worn pump
Block pickup
Low oil
Crap oil
Blocked sender
Faulty sender/gauge/wires
Other problems
Oil pressure relief valve, ball/spring upgrade
I finally went for the oil pressure valve mod. I recently
obtained a spare valve/spring etc. from a scrap engine, so decided it was 'safe'
to have a go.
The only other part required is the ball bearing from a Mini CV joint
(9/16" dia.) - the same scrap engine also had drive shafts attached ;)
The trickiest part of the procedure is shortening the spring. The way I did it
was to score the spring with side-cutters at the point I wanted to cut it,
and then to twist the 'offcut' part - due to the fact it is fairly hard,
the spring easily snaps at this point. To keep the spring in shape it
helps if it is held on a former while this is done - I happen to have a large
screwdriver in my tool box which is just the right diameter.
I removed 11mm off the free length of the spring - approx. 3 coils, not counting
the 1/2 coil at the end of the spring. (I measured the original spring at 72mm
free length, and the cut spring at 61mm.)
Then remove the original spring/plunger, and feed the
ball into the valve, followed by the spring (uncut end onto ball) and replace
the cap. Run the engine and note the oil pressure - if it's still too high, then
remove some more off the spring.
My engine now runs at 50 psi. +/- 5 psi at all revs/temperature! (That I have
experienced so far.) The oil pressure is remarkably constant, only rising a
little with revs, although it has a tendency to dip at a certain rev value
(probably related to the resonant freq of the spring) during acceleration.
To make a fully adjustable relief valve, the dome nut needs to be drilled/tapped
to accept a bolt/locknut - then the bolt can act on the spring (which needs to
be slightly shorter for this application) to modify the pressure - the locknut
is then tightened to hold the setting.