Ultimate Oil Pressure Relief Valve Thread

[rs-vic]

A question, is it better to also replace the safety valve piston with the grooved style in early engines that have had the bypass done?

[304065]

Originally Posted by rs-vic

A question, is it better to also replace the safety valve piston with the grooved style in early engines that have had the bypass done?

It is REQUIRED. If you do the bypass and use the old piston with the holes the engine will not make oil pressure.

[rs-vic]

I know it is required for the relief valve, I am asking about the safety valve, the horizontal one.

[brighton911]

I ran into an oil pressure issue I thought worth posting. While doing my engine rebuild this winter, I replaced both the oil pressure relief and safety springs. The new safety spring was 3 mm longer than the original so some set had taken place on the original. Strangely, the new relief spring was about 1.5 mm shorter than the original but still within stated tolerance. My oil pressure had always been good increasing to about 4.2 bar at 5000. Since the rebuild, oil pressure did not increase after 4000 rpm, 3.7 bar was max.

RPM BAR
idle 1.25
2000 2.8
3000 3.7
4000 3.7

As the pressures at lower RPM's were good, only low at the max end, I felt it was a pressure relief issue. I removed the new spring (messy) and replaced it with the original - yes, I keep old stuff just in case. Even though the lengths were close, I now had 4.2 or better pressure after 4000. I did not check the spring pressure at various lengths but it would appear the old one has more seat pressure than the new spring. Moral of the story, new is not a guaranty of good.

[eclipse66]

I ran into an issue of oil pressure running too high after doing the oil bypass mod on my 70, 2.2L. I shut it down and did more searches and found this posted by Chuck Moreland:

Need help. Too much oil pressure blowing up coolers

Certainly shows that this is not a "cookbook" change for every engine. You MUST use the new pistons, but need to be careful to have the correct spring length and the correct cap because of the machined depth inside. For my application I went back to the original 70 2.2L spring lengths and caps and all is good.

[Trackrash]

What luck that I just happened upon this thread.

I am rebuilding a new to me early 78 SC motor. I have not seen mention of the mods needed to update the oil pressure and scavenge systems on this motor in other publications.

BTW does anyone know the part number for the venturi screen shown in post #48, or a source? I am not finding it in Pelican's catalog.

[KTL]

Gordon,

The old part number is 90110138001 and has been superceded by 93010731400. Pelican says the original part is NLA but you might try searching around a bit. I did a part number search on Sonnen's parts website and it comes up as an apparent valid part number. I would call them, or your favorite dealer, and check on its availability.

I would strongly recommend you stay away from the aftermarket URO part. Numerous people have had fitment & quality problems with that reproduction part.

[figoulu]

Hi guys !

I have a 964 C2. I remove the oil relief screw to check about potential causes of low oil pressure at idle when the engine is at operation temp (say the needle at 8.30). When removing it, I discovered that the spring was broken, and want to remove the piston as well. Of course, I'm now stuck with the piston that doesnt move after many tries, using different methods and "tools". I even try using a hot blower, but nothing...

I have now 2 thoughts:

- Trying to crank the engine without the DME 2 ou 3 times, because I guess the oil pressure will push it down (I could attach a weight (200g) to it , to help pulling the piston down). I hope it could be a solution. My theory is that the piston couldn't come because of the oil making a perfect vacum between the well and the piston. No air is able to come to release the piston. That's my understanding of the situation.

- Exploring one comment that was done at the begining of this threat, suggesting to come over from the pressure / temp sender fixture with a rod, gently pushing on the top of the piston... Surprisingly no more comment about that was done, and the more I look my pics, the more I feel that it's more about the little well next to it (closed with a plug and washer) but certainly not from the senders cap.

Any ideas or sugestion to support my solutions ?

Thanks

[figoulu]

Here is what I can suspect to be the well to access and push the top of the piston. See the vertical moulding in the crankcase

[IMG]SAM_1813 by figoulu, sur Flickr[/IMG]

And here is what I could get. Picture taken during the overhaul of the engine, before the spring broke...

[IMG]SAM_1815 by figoulu, sur Flickr[/IMG]

[KTL]

Try one of these neat little tools? Oil Pressure Relief Plug Extractor – STOMSKI RACING LC

Steve Stomski is a great guy and $42 to patronize his support of the 911 racing and repair community is money well spent in my opinion

[figoulu]

Thanks Kevin ! By chance I found a guy next to my place that will lend me one, but for VW... I'll see if it brings something and if it can go inside the well...
I had another thought about blowing high pressure air from the top of the well located over the crankcase next to the pressure sender unit. Any feedback ?

[KTL]

The problem with blowing air thru the port in the top of the engine case is that there are many oiling holes beyond that location that will allow the air to escape. I would continue working on a mechanical method of extracting the piston.

[304065]

See photo on p.1 of this thread-- the pressure relief piston is at the bottom of a vertical passage topped by the oil pressure sender. Remove the sender and stick something that is NOT metal down there to gently push on the piston top. You do NOT want to mar the passage, or have something break off, or disintegrate etc.

If the piston is truly stuck there is a nonzero chance you will mar the passage anyway, but there's not much you can do about that.

[figoulu]

Originally Posted by KTL

The problem with blowing air thru the port in the top of the engine case is that there are many oiling holes beyond that location that will allow the air to escape. I would continue working on a mechanical method of extracting the piston.

Yep Kevin, I've been thinking about the same, you're right, the air will flow elsewhere anyway

[figoulu]

Originally Posted by 304065

See photo on p.1 of this thread-- the pressure relief piston is at the bottom of a vertical passage topped by the oil pressure sender.

I caught the idea yes, but it's not topped by the sender unit. My conviction is that it's the well next to it that is in relation with the piston top.

[figoulu]

End of the story... The piston came off today with the tool comparable with Stomsky's
I found a piece of metal with it. Was it on the ground of my garage or really with it ? I'll never know but the well was in a good shape. I could replace everything by new parts, and eventually gained +0.2 / 0.4 bar of oil pressure. Thanks for your help.

[MikeD]

I realize this is an old thread, but a very useful one. I have read it numerous times over the years, and was always confused by some inconsistencies in the data. So here are my thoughts...

1. Why did Porsche change the spring? The explanation of "loss of oil pressure during high speed driving" suggests a scavenge problem. Too much oil in the sump, not enough in the tank. Why? If at high speed you are running just below the bypass pressure, you could end up overwhelming the (smaller) scavenge pump. Solution: increase the bypass oil? Based on my calculations, the long spring allows the piston to open much further, which should flow more oil.

2. Do you have to use the new plunger in the "safety" circuit. No. I think Porsche just kept the caps and plungers the same so they wouldn't get mixed.

3. Why do you need an anti buckle rod for a spring that's captured in a hole? You don't, although in the manual it stresses keeping the spring away from the bore to prevent damage. Mostly I think it is a limit stop to keep the piston from over travelling and taking the spring to solid height, which over time will fatigue it.

4. Why do the two spring behave differently, all other things being equal. For fresh springs, they should open at about the same pressure, but the long spring allows the piston to open much further. I calculate the long spring piston opens 15mm at 75 psi whereas the short spring opens 5mm. From the diagrams 5mm is enough... I surmise that the larger opening allows more oil to bypass, and maybe minimizes viscosity effects.

5. What is the effect of the "pop" feature? I think it does two things. One it makes sure the piston stays open when it opens as described on pg. 1. Two, it controls the closing pressure and the amount of travel. My calculations say the both short and long spring open at 76 psi and close at 50 psi.

6. What about the 12mm and 9mm caps? On the pressure relief with the short spring, you should use the 12mm cap. If you use the 9mm cap your valve will open at 95psi instead of 76. This can be a good substitute for shimming the spring if your pressure is too low. On my 3.2 I machined out the new style cap to 12mm as the pressure was too high with the short spring and 9mm cap. On the safety, with the 9mm cap you get the more like 130psi than the original 113psi.

7. Holey piston. One thing that hasn't been mentioned is if you use the holey piston with the bypass mod, the oil tank will drain into the sump, through the little bleed hole below the piston. And the pump will try to suck oil/air out of the sump as mentioned.

8. Long spring with spacer... if that spacer is about 4mm thick, it would increase the opening pressure from 75 to 85 and the closing from 50 to 55.

These calculations are based on spring rates calculated from springs I have. I calculate 32 lb/in for the short spring, and 11.6 lb/in for the long one. These spring rates are much higher than the attributed to Aaron B. on pg. 1. YMMV. Also, the spring measurements on pg. 1 from the workshop manual appear to be incorrect (wire dia too small, rate too low). What is useful in the manual is the installed length of 59.5mm with the 12mm cap.

Hope this help someone and doesn't confuse things more.

Mike