County oil pump pressure - prv spring rating

[Paul Kelley]

Anyone else had issues with the County oil pump and oil pressure being either on the high or low side? I bought it from Robsport and they state that you need to fit their adapted and lower rated prv (pessure relief valve) spring as the standard spring it is supplied with sets the pressure too high. I've tried both and the low one seems too low at 10-15 psi at idle and 30-40 cruising and accelerating, whilst the standard spring gives 20-25 idle and 50-80 cruising and accelerating. Caught between the two and wonder if anyone else has found this? Is there a 'goldilocks' version out there? If you had to choose between lower versus higher pressure, which is better? Ideas etc welcome as always.
Paul

[mole42]

I’d prefer the lower pressure one, there’s evidence that high oil pressure can damage the timing chains by over tensioning them and that higher oil pressure can result in more serious leaks. My engine has run 40psi for years, about 50,000 miles in my ownership.

[Paul Kelley]

Thanks Mole42. Yes, I've heard about high oil pressure damaging the timing chains and currently I have virtually no oil leaks. But psychologically I equate low oil pressure with a worn out engine, which certainly isn't the case with mine as it has been completely rebuilt within the last 5,000 miles. I've used both Heritage Oil and currently VR1 and new filters and get the same result, so I'm pretty sure it's the spring rating.

[wilf]

80 psi is really too much! That is jackshaft-bothering.

[flying farmer]

Use the spring that gives the lower pressure but fit a small thin washer between the spring and the cap. i find this will generally give about 10-15 psi increase.

Sometimes the cap will push in from its retaining split pin, in this case another option is to fit a thin washer between the split pin and the cap, saves removing the cap if you have the low pressure spring in there already.

Tony Hart once told me to aim for 45 psi at 2500rpm so this is the figure I always try and achieve

[DMT]

+1. I fitted a recommended spring and the pressure went through the roof, ended up with a washer under the spring and now have as per Neil.

Dave

[jbuckl]

Standard hoborne Eaton spring allows the relief port to be open fully at approximately 47.5 psi . there must be a tolerance but I don’t know that, guessing it’s about +\- 4psi.
I wouldn’t want to see any more than 50psi. Per Wilfs concern.
But there’s no gauge on my stag.
After rebuild I saw just over 45psi on initial fire up.
removed the gauge after that.

[DMT]

The "standard "spring I bought from one of the usual outlets looked to have less turns than the one I had but the pressure went up to 80 psi when cold.

[jbuckl]

The "standard "spring I bought from one of the usual outlets looked to have less turns than the one I had but the pressure went up to 80 psi when cold.

Most probably aftermarket, not hoborne Eaton.
Somewhere I have a spreadsheet with the active coils , lengths & rates for them all.

[Lingen]

Paul
You say that you are getting 30/40 psi at speed with one spring, and 50/80 with the other, and also different idling pressures. I agree the one is way too high, and the other a bit on the low side. However differing springs should not make any difference to the hot idling pressure as both springs should have fully closed the relief valve long before then. So the idling pressure should be the same with both of them. Perhaps the valve isn't seating properly?
Mike.

[Paul Kelley]

Many thanks one and all for the feedback and to Neil and Dave for the washer 'padding' tip which is what I'll try next. And Mike, good point about the valve seating. One feature of the Stag is that the oil passes through the pump before the filter so it's always possible that a tiny particle has got to work, but I do have a magnetic sump plug to counteract such stuff. I've just returned from our regional (West Yorkshire) Last of the Summer Wine end-season get together and so asked around re oil pressure. Quite a few are getting 30 + at idle with a smallish uplift to 40-50 psi on the run. All agreed that 10 at idle is on the low side, equally much over 60 is too high. Tony Hart's measure of 45 psi at 2500 rpm quoted by Neil, above, sounds like a good level to aim for. Another quoted today was at least 30 psi at 30 mph in 4th gear (manual).
I believe that the oil warning light is set to come on at 7 psi, so I will be happy with +/- 20 at idle and +/- 40-50 in general running.

[jbuckl]

On a stag engine ,
oil pressure being too high is a huge risk.
afaiaa 3.5 is oil light on.
15 at hot idle is acceptable

[richardthestag]

Paranoia central but slightly justified, especially as nobody is knocking out a suitable pressure relief spring for the stag?!?!?!?

Engineers have told me that flow is more important than pressure. This is something that I am slightly uneasy with, so there of course has to be a balance. Pressure is created by slowing the flow slightly.

45psi max with hot oil is what I always understood for the stag v8. Mine cold and max is a smidge over 50psi but doesn't rise if I rev the engine.

Hot idle is around the 30 psi mark which is perfect compared to a very used rover v8 engine where you might be lucky to see double figures oil pressure at idle and still no oil pressure warning light and it still sounds sweet

Oil pressure gauge is a fabulous diagnostic tool but most motorists do not understand what it is telling them. Thus it becomes a distraction as jbuckl Julian says.

Richard

[Triumphman]

I believe engineering practice is 10psi per 1000 revs is sufficient on plain bearing engines.

[jbuckl]

Pressure doesn’t determine the oil film thickness…. Flow, area, load, speed, viscosity & temperature does.
Thats why pressure is much more to do with worry & warning.

10psi sounds like a nice rule of thumb… there’s more to it though.