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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
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.
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