Oil pressure at head

Met a guy with a Trident who had two gages, he said that the only way to tell the real number was to look at the differance between the two.

L.A.B.

You are spot on with your comment about additional shims having no affect on the oil pressure when the oil is at operating temperature. And you are correct about there being “little” difference in oil pressure between the head and crankshaft. In fact, there should be no measurable difference in pressure between the two locations.

Jason

Testing down below should provide the same numbers. It's the same circut the volume is slightly different but that dosen't change pressure in the system. Holes leading to the crank are bigger than to the top end. Very small differance though. Like you say always learning.
It had been explained to me that there is a wave of oil spining around the big end of the crank as the thing is spinning. It uses the space provided by the clearance of the bearing. This oil and the oil in the crank cavities has it's own pressure from the spinning motion of the crank. This is another reason that I was thinking that there must be a seperation from crank to top end but it's not true. If you make the mistake of putting the rocker shafts in backwards with the cutaway faceing the push rod instead of the valve you will loose pressure all over.

Fourperf wrote.
maybe I should add a shim which would make 4 total. The oil pressure would be over 100lbs at idle when cold but maybe that would get me closer when hot
Not really a good idea, as the name implies it is an excess pressure relief valve and will have no effect on your hot oil pressure, if your pump and shell clearances can only make 40 psi when hot thats all your going to get regardless of weather you have 100 lbs or 200 lbs in there.
What you do have the big risk of though is imagine this scenario. You are just leaving the pub/bike meet and want to impress your mates with what a real bike sounds like at 5k+ revs leaving, the bike is stone cold on a cold night and your 20/50 is like treacle, you haven't got time to gentley warm it up for five miles so off you blast. The PRF is set for 100lbs and your gauge is reading 100 lbs, what gives, the oil seal in the the timing cover feeding the crank blows inside out now you have no oil pressure.
Set the PRF to give 60 psi when cold and forget about it. Nortons do run low oil pressure when hot. I dont have a gauge on mine but I have a switch connected in the rocker feed between the head feeds conneted to a warning lamp in the headlight. Hot idle the light will flicker on. Another example is an engineer friend who built a 920 Rob North with an oil pressure gauge, I asked him what the hot idle was, about 0 psi.
Norton probably never fitted oil pressure gauges or warning lights for fear of frightening owners into thinking they had a problem.
regards

that makes a lot of sense to my inexperienced small head.

Thanks a lot

mark

well, after pondering this topic all last night and on my run this morning (even though it was stated in an earlier post) I think I got it. The relief valve is set with the shims to relieve pressure at a certain pressure which you set with your guage, so the shims should have no effect on the pressure once warm and the oil pressure drops a bit because it never reaches that set point. I hope thats right. I feel like such a dunce.

Mark

I agree with Snakehips. I've run an oil pressure gauge on mine ever since I rebuilt it and have always been troubled by the way the oil pressure drops when it gets real hot. Idle pressure on a 90+ day would be maybe 5 psi. Recently, I had a near get-off when my rear tire slid out from under me and the correction I had to do to stay on was so violent that it broke the sheet metal bracket that holds the voltaeg inverter that drives the electric gauge, so the gauge no longer works. I didn't feel like fixing it and I still have an idiot light that works, and now I like things much better! It's been unusually hot here this year and I've been happily riding without really knowing what my oil pressure is. Ignorance really is bliss!

pressure gauge

Well i'm ready to change my mind on installing a pressure gauge.
I've had the bike since late seventies. and never worried about it.
I guess after all these years i'm wondering if the oil pump is still pumping like it should!
I might hook one up temporarily and forget about a permanent fixture.
Thanks every one for the input. Its been a really informative topic!