Shiming the oil pressure spring?!?! HELP :(

[911-lightning]

Hi,

The oil pressure on my 911 SC is very low
So I read in the "how to rebuild" that one possible source could be that there is something wrong with the oil pressure spring.

I am about to change them and the book says something about shimming the vertical pressure spring with 6mm washers.

So for the question. Where should I put the washers??

Inside the piston? Inside the pressure relief cap? Slide them on the pressure relief sleeve?

And the washer, is the 6mm the hole size on the washer or the washer itself?


Hope someone can help me with some good advice

[911-lightning]

If someone have a picture illustration that would be PERFECT!!!

[4sd911]

The oil pressure relief works around 88 psi. This only works when the oil is cold and pressure is to high. Low oil pressure would be a different problem. One try to increase oil pressure would be to install the cam line restrictor Pelican Parts - Product Information: PEL-CAMRSTN To check if you have one there will be a grove around the outer hex portion of the fitting (around the middle where the wrench fits). This uses a smaller hole for the oil to pass through to the cam towers.

[ludvikagard]

If You havent, I suggest You make shure that the pressure youre reading is correct by connecting a manometer at the pressure sending unit. My pressure gauge showed 2 bars while the actual pressure was close to 4.

[911-lightning]

Originally Posted by ludvikagard

If You havent, I suggest You make shure that the pressure youre reading is correct by connecting a manometer at the pressure sending unit. My pressure gauge showed 2 bars while the actual pressure was close to 4.

Is this the unit that is located beside the fan house? The sender to the right of the fan house (if looking in the driving direction)?

Do the oil need to be drained before one can swap the existing unit with an manometer??

Thanks

[911-lightning]

Originally Posted by 4sd911

The oil pressure relief works around 88 psi. This only works when the oil is cold and pressure is to high. Low oil pressure would be a different problem. One try to increase oil pressure would be to install the cam line restrictor Pelican Parts - Product Information: PEL-CAMRSTN To check if you have one there will be a grove around the outer hex portion of the fitting (around the middle where the wrench fits). This uses a smaller hole for the oil to pass through to the cam towers.

So shimming the oil pressure relief spring will not help on building pressure when the engine is hot?
Y do everyone list this as an possibility to raising the pressure if it is only on an cold engine?!

[4sd911]

Originally Posted by 911-lightning

So shimming the oil pressure relief spring will not help on building pressure when the engine is hot?
Y do everyone list this as an possibility to raising the pressure if it is only on an cold engine?!

Well I'm no expert but I would like someone to explain if I'm wrong.

[bazar01]

Originally Posted by 911-lightning

So shimming the oil pressure relief spring will not help on building pressure when the engine is hot?
Y do everyone list this as an possibility to raising the pressure if it is only on an cold engine?!

Shimming will increase oil pressure both when cold and hot if the spring rate has deteriorated.

Since shimming is the easiest thing to do compared to attaching a mechanical oil pressure gauge on the oil pressure sensor tap in the back of the engine, I would try this first. Try putting a 1 mm thick washer on the spring seat and see if the oil pressure reading improves.

Well, on a side note, there is no amount of shimming can fix a low oil pressure reading if the engine has mechanical issues.

[4sd911]

Be careful, to high of a cold oil pressure can burst the oil cooler.

[ludvikagard]

Quote de ludvikagard

If You havent, I suggest You make shure that the pressure youre reading is correct by connecting a manometer at the pressure sending unit. My pressure gauge showed 2 bars while the actual pressure was close to 4.

Is this the unit that is located beside the fan house? The sender to the right of the fan house (if looking in the driving direction)?



Do the oil need to be drained before one can swap the existing unit with an manometer??



Thanks

If i remember it right You should be able to swap the pressure sender (the big round one to the right of the fan) with a manometer. No need to drain. Just make shure the engine is turned off

[Walt Fricke]

No issues at all removing the oil pressure sender and installing a new one or something else, like a mechanical gauge. But the senders use an M10x1.0 thread, or on some later cars a much larger thread (M14? 16?). The typical pressure gauge you can get from a good hardware store or many other sources is likely to have 1/8" NPT threads, which look an awful lot lime M10x1.0, but won't work. You can purchase adapters. Or fabricate/kludge something. Once in the NPT world you can easily get an adapter if your gauge is 1/4" NPT.




To deal with an oil pressure issue I have, I also converted the two plugs which hold the springs in place so the spring perches could be adjusted. Shown is the relief plug - the one which should only come into play if the regular pressure setting spring isn't able to relieve enough pressure. This is probably overkill, and something like this will also give a higher base setting (similar to shimming). In my case, with no engine oil cooler to worry about, shouldn't matter. If the other one solves my problems I can probably go back to stock plugs and shim things.



I'll know in a couple of weeks if this solves my problem, after I get the engine back in the car so I can run it.

[trak ratt]

Originally Posted by 911-lightning

So shimming the oil pressure relief spring will not help on building pressure when the engine is hot?
Y do everyone list this as an possibility to raising the pressure if it is only on an cold engine?!

Most complain about low oil pressure at low RPMs. Since the relief spring controls oil pressure at the upper end (~6 bar) shimming won't help raise hot oil pressure UNLESS the spring is so badly worn that it opens the bypass valve at way lower pressure than spec. If the spring is so badly worn that it lowers the oil pressure in the high RPMS then shimming will help. But long term the spring should be replaced.
Most, including me have had good luck raising low RPM oil pressure by using the new improved cam oil pressure restrictors mentioned earlier.

Lot's of things can cause low oil pressure, few are cheep or easy to fix. Checking the oil pressure Gauge/sending unit before doing first makes a lot of sense.

[Walt Fricke]

Springs don't lose rate. What they can do, if coil springs, is lose coil length. Which means they have less initial seat pressure if initially compressed. And will go into coil bind sooner.

Absent coil bind, shimming a shortened spring will restore its operating characteristics.

Just as resetting a torsion bar which has "sagged" will.

New springs are not expensive. The short overpressure relief one is used in the GT3 and Cup motors of 2012, same part as in 1965.

[KTL]

Cold, high oil pressure won't burst the oil cooler(s). Not the engine cooler, and not the auxiliary front oil cooler, as long as both the internal engine thermostat and the external thermostat are in place and are working properly. Meaning, the two t-stats are closed at cold startup oil pressure and neither oil cooler is seeing any oil.



One of the very nice features of the factory Porsche t-stat, compared to say the common Mocal replacement, is that it too has a built-in pressure relief. The Mocal is just a straight t-stat.


You can see in the diagram how the engine deals with overpressure at dead cold temps. The pressure relief piston bleeds off pressure by directing oil back to the inlet side of the pressure pump. When there's severe overpressure, the safety relief piston kicks into action and dumps oil back to the engine sump.

[917guy]

One of my first mini projects when I got my own lathe in the 80s was to make a pair of replacement relief spring caps. Aluminum, with 2 levels of extra force, with a longer spring. Adding a washer is easier, but I wanted a little project, and they still look nice.

On my 1972, I can push the plunger to open the vertical relief a bit, using a 10mm aluminum rod from the port above it, beside the thermostat. It should take 20+ pounds of dead weight to crack it open a bit.

This is a quick way to calibrate what the spring is actually doing at the point of cracking it open. I put the actual calculation in the May issue of my red river sports car enthusiast magazine, but I do not have it near me.

David

[Grady Clay]

911-lightning,

Exactly what is your “low oil pressure” situation?
What is your oil pressure hot & cold at each 1000 rpm (1000 to 6000 rpm)?
Our 911s indicate very low pressure at idle when hot.
‘Normal’ is about 1 bar for every 1000 rpm to a ‘normal’ max of about 4-5 bar.

Thus far this discussion has been about potential ‘fixes’ and not diagnosing to see if there is a problem.

For accurate diagnosis, follow Walt’s advice and use a calibrated mechanical gauge.


There are a number of different oil pressure regulating/limiting cap, spring and piston configurations.
With a ‘box of parts’, it is easy to get an incorrect configuration.
Leave it as original.

Again, welcome.

Best,
Grady