New Oil Pump Pressure

[V Mad]

As far as I know new oil pumps have higher pressure than original. I have a new pump fitted to my new engine, but rather than fit it and have to deal with it later I would rather sort it now.

Has anyone found a solution to this that works? Can you help?

[marshman]

As far as I know new oil pumps have higher pressure than original. I have a new pump fitted to my new engine, but rather than fit it and have to deal with it later I would rather sort it now.

Has anyone found a solution to this that works? Can you help?

Hi Chris,

This problem surfaced just over 2 years ago. To cut a long story short the County pumps had the wrong spec relief valve spring fitted. I got round the problem by fitting an old spring - this was after a lot of too-ing and fro-ing and being told by county there was nothing wrong! (not if you like your oil pressure to be 100psi!)

Have a look through these threads from 2009. Not sure if pumps being purchased now have the correct spring fitted.

http://www.stag.org.uk/forum/showthread.php?6705-Timing-chains-Knocking-Noises-amp-Excess-Oil-pressure&highlight=pressure

http://www.stag.org.uk/forum/showthread.php?4490-Oil-Pressure/page3&highlight=pressure

http://www.stag.org.uk/forum/showthread.php?6088-Ridiculously-High-Oil-Pressure&highlight=pressure

Roger

[marshman]

Here are the pics of the two springs.

[flying farmer]

I have had this problem too, and also got round it by fitting an old spring, however this was a bit weak and needed a thin washer behind it to up the pressure to 45-50 psi hot.
Since it is a real pain to get the pressure relief valve spring out without removing the pump, before I fit my oil pumps I always weld half a washer to the PRV cap. The split pin goes through the hole in the washer, and it gives something with which to pull the spring cap out. It makes changing or shimming the spring a 5 minute job.
Neil

[flying farmer]

Picture of the pump with washer installedDSCF0096 (450 x 600).jpg

[marshman]

Since it is a real pain to get the pressure relief valve spring out without removing the pump, before I fit my oil pumps I always weld half a washer to the PRV cap. The split pin goes through the hole in the washer, and it gives something with which to pull the spring cap out. It makes changing or shimming the spring a 5 minute job.
Neil

If the pump is already fitted then you can put a bowl under the car, remove the slit pin from the pump then turn the engine over to build up oil pressure, this will force the cap out, you then just have to find it! hopefully it falls into the bowl. This worked for me.

Roger

[Moraystag]

Same here gent's used old spring in the new county pump a couple of years ago. No problems so far.
The spring that came with the county pump was slightly longer if I remember rightly.

Mike

[V Mad]

Some good info there, thanks.

I dont have an old pump to hand so cannot use the old spring. Seeing as there is a section of closed coils, then if the spring is longer than standard, I think I can cut a small amount off the closed end to make it the 'correct' length whatever that is?

The photo shows a spring of about 4.8 cm. I take it that the longer one? My spring measures 4.4cm so I think that might be OK, what do you think?

[V Mad]

Picture of the pump with washer installed[ATTACH=CONFIG]14421[/ATTACH]

I have now done the same, washer welded on.

I took out the spring and although it is short at 44mm, it does not have so many free coils so I think it is still high pressure. I measured the deflection at 1.83mm per kg. I am not sure what that relates to as oil pressure but at least now I can install it and remove more easily if needed.
stags misc 033.jpg

[dasadrew]

Also quite a bit of info on oil pump spring sizes and rates and their effect on pressure on the Stag resto thread posts 401 to 419

http://www.stag.org.uk/forum/showthread.php?8032-The-White-Blue-Bavarian-Stag/page11&highlight=pump

[V Mad]

Drew, thanks for that, really useful. My spring deflection was 5.5mmm at 3kg (29.4N). So 29.4/5.5 gives 5.35 N/mm which is very close to your figure of 5.3 for the too strong County spring. So I need to change that now, no point in fitting it.

I take it no one sells the correct springs, and I will have to find an old spring? I wonder if Peter H at LD would get some made for us (if not I might get involved!). We cannot accept this situtation, something has to be done to preserve our precious engines!!

I may get a quote based on the following spec; any comments please on suitability of spec: note rate can always be increased with spacers so I have kept it on the low side. Note max compr length taken from County spring.

COIL SPRING DATA: TYPE COMPRESSION; APPLICATION AUTOMOTIVE OIL PUMP PRESSURE RELIEF; ID 10.6 MIN; OD 14.0 MAX TOTAL LENGTH COMPRESSED 28 MAX.
RATE: 3.5 N/mm +/- 0.25 tba

[ChasR]

For future reference going from previous threads I have read, I believe that TD Fitchett supply reconditioned pumps (the original Stag items) which pump the correct oil pressure .

[davidf]

Hi
Back in the 80's or early 90's, I had a sudden drop in hot tick-over oil pressure on a fairly new engine. After a few days of panic, I checked out the oil pump spring. My first reaction was that it didn't look like a good design for a relief valve spring. Anyway, to prove whether this was my problem, I put a washer under the split pin, and sure enough, higher pressure all across the operating range, so the problem was definitely in the relief valve. Next, I took an old pump and spring into our design office (I worked for a manufacturer of very sophisticaed valves in those days). Well, the guys in the DO just fell about laughing when they saw the spring. It is rubbish. The principle of a releif valve is to have the crack pressure and full flow pressure as near as possible the same. So, that needs quite a "soft" spring with quite a high pre-load in its assembled state. The idea of having any closed coils is about as far from ideal as it is possible to get. They designed a new spring for me, and I got one made up. Result was super - pretty consistent pressure across all operating modes. It is a very odd looking spring; quite long, thinner wire, and very open coils. So, I got a batch of about 50 made, and sold them on to fellow members; everyone liked them at the time. I don't have any more left, and no easy access to spring manufacturers any more, but I am quite happy to post the design. Only problem; I am away from home just now, so it will be a couple of weeks before I get back to my home PC, where I have this spec. I think I also have the calculated crack pressure and full flow pressure of the standard spring - crack pressure was very low, so you will get very low oil pressure at hot tick-over.