911 2.0L oil springs question.

[Lyndon302]

I have a stock 67S
I've been reading about relief and safety oil springs. I'm now really confused.
What plugs,springs and pistons do I need to bring it up to contempary thinking.
Thanks lyndon

[Lyndon302]

This is what I have
This is what I have purchased.
STD 2.0L case and pump.
Am I correct in fitting these parts.
Lyndon

[Walt Fricke]

No - reuse what you have.

Or learn how (search on the engine forum) to do the modification needed to use the new stuff. The modification sends the "excess" oil from the pressure regulating piston through a hole you drill in the case (while it is apart) which sends the exiting oil back to the intake side of the oil pump. And you tap the outside (internal case side) of the hole you drilled, and screw in a plug.

If you have not, and don't plan to split the case, you can't do the mod and can't use the new stuff - at least not the taller spring and new pistons. Somewhere in those new parts should be a hollow tube, which goes inside the longer spring, too. That is part of the newer setup, which came out about 1977.

[Lyndon302]

Walt
Thanks for the input.
Yep it's lasted 55 years as it is
I have split the case. Im not confident of anyone modifying my cases where I live.
I have researched this and found.
If you modify your the case you have to upgrade. ( Pistons seem the issue here)
If you don't you at least should upgrade the pistons.
One spring is the same ?
The other is longer but weaker ( thus the inner tube so when it buckles it does not wear the bore.)
I believe some pressures have been changed.
I just can't get a difinitive answer and as you know it needs to spot on.
Thanks lyndon

[SBell]

According to Wayne's book if you have not done the bypass modification to the case then you must use your original style pistons. If you use the new pistons without the bypass mod the engine will not make oil pressure.

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[Lyndon302]

Originally Posted by SBell

According to Wayne's book if you have not done the bypass modification to the case then you must use your original style pistons. If you use the new pistons without the bypass mod the engine will not make oil pressure.

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I thought it was the other way around ??
To be safe I may put it back the way it came apart
Lyndon

[SBell]

Originally Posted by Lyndon302

I thought it was the other way around ??

To be safe I may put it back the way it came apart

Lyndon

I don't have the book in front of me so you could be right.

[Walt Fricke]

Guys - I, along with a lot of others who know more than I do, don't need a book in front of us, but SBell has it just right
.
Without the upgrade, there is only one part (plus perhaps the new plug and plug gasket) you can reliably use from what you bought: the new short spring. And the old short spring is most likely just fine. Engines spend most of their life not running, and that short spring only has pressure above a maximum applied to it if the pump somehow starts producing way more pressure than the pressure regulating spring normally allows. Springs never lose rate, though if way overstressed a coil spring's coils may get closer together. Not an issue here.

You cannot - repeat cannot - use the new piston in the vertical, base pressure regulation, hole. And you can't use the new, longer spring in that hole either. If it isn't too long, I suppose you could stick the tube in there, but why - it isn't needed. As a legendary GM chief once said, parts you don't use cost nothing, and can't fail.

The one on the side uses the same spring, new and old. No reason to replace it, but you can use the new short spring there if it makes you feel better.

Since no modification needs to be made to the horizontal stuff, it is not clear to me that the new piston wouldn't work there. It only opens if the pressure is unsafely high despite the main piston doing its pressure regulation job - if you have a serious overpressure, well above, say, maybe 90 psi, the horizontal piston sends the oil into the sump the same as always. But your old pistons look fine, and do you want to experiment just to experiment? You can sell the whole bunch of new parts to someone who is willing to make the modification.

I did the modification myself, with hand tools, power and manual. The hardest part was putting a nick on the side of a hole so I could get the drill bit to start drilling at a fairly low angle relative to what you usually drill holes at. I used a die grinder with a cylindrical burr to grind a notch, drilled a pilot, and then to the recommended size. Any machine shop could do this easily in a number of ways. Using the search function, especially on the engine forum, you can find descriptions of how to do this.

A couple of hints: If you aren't buying my spiel, transfer this post to the engine rebuilding forum - that's where some super experienced shop owners and professional mechanics help us amateurs out.

And purchase our host's book on how to rebuild and modify the aircooled engines through the 3.2s. Pelican, of course, sells it. Page 52 and 53 in my, now old, edition. Use the index.

And do a search, like the complete oil pressure thread, or just case oil pressure modification. Maybe someone has given a complete blow by blow with pictures on how to do the modification.

However, Porsche didn't do this until about 1976 or 7 (my '77, made summer of '76, had it), and won a lot of races and made a lot of pretty durable cars before they did that. Me, I wouldn't think of not doing it. But for a street car I'd suspect it is hardly necessary for a successful home rebuild. Bruce Anderson (his book on the 911 is very useful to have) says you really need the modification if you are either racing the engine, or have installed a later oil pump. Otherwise, he didn't think it mattered.

[Lyndon302]

Sounds like sound advice back in with old
( New seals )
Lyndon