Oil pressure relief valves old or new?

[Robbie123]

Hello, let me introduce myself. I am rob and live in europe and i am rebuilding a porsche 911 from 1976 which i bought with an engine from 1974. Thanks to this Great forum and Waynes book i have been able to tackle almost every problem i had during the rebuild of my engine. I already have it in my car and even running.

I am really happy with the result but i have one problem. I do have little oil pressure with motor running at idle. That is at idle the gauge Will not mesure anything but at 3000 rpm about 3 bar. I did check if the problem was my gauge but it is fine, the meter is new. I intstalled a mechanical gauge and had the same readings.

I do have oil running everywhere when i open up different parts of the engine. The engine seems to run fine and makes no noise at all and the idiot light stays out all the time. I had the engine running for more than 30 minuten already at idle or higher rpm.

I think the problem is my oil pressure relief valve. I have the old style one in the engine with the holes in it. The problem is that i do not know if the engine had the oil bypass modification done , i did build the engine myself and i did not have it done but it might have been done before me.........

Is there any way to control this without getting the engine out of the car or can i just try to install the new valves without the holes and look what happens?

If i do not have the bypass done in my engine can i than still put the new style valves in my car or Will this destroy my engine?


Thanks very much for all information.

[Flat6pac]

At idle, the oil light is out. That represents flow.
Pressure is the resistance to flow. 3 bar at 3K you're good to go.
I would think that someone who took time to drill the bypass would know enough to do the rest of the job.
There is, as I recall, different spring lengths in one position.
Bruce

[Robbie123]

Thank you for your answer. The problem is that the guy i bought the car from did only dismantle the engine and never put it back together.....

I can't reach him anymore to ask and i am not even sure he took the engine apart himself.

It ist true that with the bypass you should have different springlengths and i do not have them so that might be an indication that i do not have the bypass.

But is it not possible to see the bypass without taking the engine apart?

[Walt Fricke]

The pressure setting piston is the vertical one. The old stock bypass hole is in the rear of that cylinder. If you pull all the stuff out of that vertical bore, you could put a borescope with a right angle end up the bore. Somewhere up toward the top you should see a round hole facing to the rear - that's where the excess oil goes - into that hole. The hole is bored in parallel to the ground from the flywheel side of the engine, if memory serves, and goes through the pressure setting vertical bore, and out the back side and eventually into the engine case - the internal space where the crank and oil and stuff is.

The modification consists of two things other than different pistons and springs. First, with the engine apart, you drill a hole from the inside of this relief bore diagonally to the front right. This intercepts where the oil from the oil tank comes in, before the pump. That was the deal - send excess oil right back around, and not into the case sump.

The second part of the modification involved tapping the hole where the oil used to dump into the case, and screwing in a plug so it can't do that.

Bruce Anderson's book has some pictures, I think. You could search Pelican and find pictures.

You just might be able to see if there is a plug down that horizontal cross hole. Maybe.

No way to see it without a borescope. Less than $200 at Harbor Freight will get you one. But no guarantee that you can get it pointed where you need it, or that the light is good enough to illuminate the plug, or to show the angled hole.

[Robbie123]

Thank you walt for your answer. I Will ask Some friends of mine if anyone has a scope to take a look in there.

If nobody has one could i just try the new style valves with the new springs or Will that destroy my engine if i do not have the bypass done?

Rob

[Walt Fricke]

I've seen explanations for why the change from the piston with holds in its sides to this design, but don't recall them. What I recall mostly is warnings not to use the wrong one. That would be my message to you - don't experiment like this.

It is pretty unlikely that someone would know how to do the oiling mod and not realize you needed different springs and pistons. Every reference to this modification describes this. If you have the old style pistons, I'd use those if I couldn't confirm anything with a borescope. And I am just suggesting the borescope method, as I have not tried this myself, though I have a borescope and find it useful, if not without difficulty interpreting what you see on occasion.

[47silver]

Can you see it through the dump plate or feel the plug?

[Walt Fricke]

Nope - the oil pump is in the way.