Why - oil by-pass mod

[Forssling]

Hi All, I and my friend is working on my 2.2T engine.

I am not doing any big upgrades performance vise. I will not upgrade to pressure fed tensioners, just the collapse stops. I will run the original oil pump.

Should I do the oil by-pass mod? What is the reason for this mod?

All input appreciated.

Jörgen Forssling
Gothenburg
SWEDEN

[stownsen914]

The bypass mod takes the oil that gets past the oil pressure relief valve and redirects it to the inlet of the pressure side of the oil pump, instead of dumping it into the sump where the scavenge side of the pump has to pick it up. The mod somewhat reduces the work the scavenge pump has to do. Effectively this means less oil sloshing around the sump, which is a good thing. Some will tell you that a later style pump must be used, I kept my early pump and didn’t notice any issue. Extra oil at the inlet to the pressure side of the pump can’t do any harm.

[Forssling]

Thanks for your input!

//Jörgen

[Forssling]

Hi again, reviving this thread...

Just to check my understanding, the only thing I need to replace is the pressure relief valve piston to the later style without holes. I can use original spring and plug.

Is this correct?

Thanks for your input,
Jörgen

[cmcfaul]

I believe there is machining of the case involved. A worth while upgrade as these cars did not make a lot of oil pressure (near zero at idle) so anything helps.

Chris
73 e

[stownsen914]

You have to machine a hole in the case, and plug an existing hole. It’s important to make the new hole precisely. I think most people have a experience Porsche machinist do it. There used to be a kit you could buy with a drill jig to make the new hole, and a tap + pipe plug to plug the old hole.

And I was thinking that the spring was different too, but maybe my memory is failing me?

[Daves911L]

The oil bypass mod is only necessary if you are using a later oil pump. Around 1977 or so Porsche increased the pressure side, and decreased the scavenge side of the pump. The overall dimensions didn't change, but the proportions of the two separate pump chambers differs. Most people never noticed, but if you happened to be a guy running high RPMs for long periods of time, the scavange pump couldn't keep up and eventually your case filled with oil, leaving nothing in the oil tank to be pumped to the bearings, and engine failures did occur. There were a series of service bulletins through about 1980 offereing various fixes, finally resolved with the bypass mod, different bypass pistons, and springs. I don't think it will hurt your 2.2 if you do it, but neither will it help it, unless you are using one of the later oil pumps with the small scavenge housing.

On a side note, a friend of mine had one of the very first 911SC's in the country. He had an uncommonly heavy right foot, and zero respect for law enforcement. He grenaded that engine within a few weeks, with what we now know was the classic sustained high rpm oil starvation issue. The dealership scratched their head (ass?) over the issue for a while, before eventually a new engine arrived in a crate, with orders to return the old mill for dissection in Germany.

[Forssling]

Hi All, and thanks for your input. Yes of course, the drilling of an extra hole and the plug in the old, but I was thinking hardware.

Is it only the new model valve piston? Spring too? Anything else?

I have heard a lot of people doing the oil bypass mod and leaving the old pump in. As Stownsen914 say "Extra oil at the inlet to the pressure side of the pump can’t do any harm." Right?

//Jörgen

[stownsen914]

Daves911L - I think you may be mixing two different oil system updates that Porsche did. The oil bypass mod was done for the 2.7L motors. The issue you mention with the 911SC where the crankcase would fill with oil was a scavenging issue that they fixed with (I believe) an updated sump screen design.

The oil bypass mod reduces oil in the sump and increases supply to the pressure side of the pump. You can switch to the later style pump in conjunction with the mod, but it isn't necessary.

[Daves911L]

Originally Posted by stownsen914

Daves911L - I think you may be mixing two different oil system updates that Porsche did. The oil bypass mod was done for the 2.7L motors. The issue you mention with the 911SC where the crankcase would fill with oil was a scavenging issue that they fixed with (I believe) an updated sump screen design.

The oil bypass mod reduces oil in the sump and increases supply to the pressure side of the pump. You can switch to the later style pump in conjunction with the mod, but it isn't necessary.

I know the 2.7's don't have the pressure relief ported back to the scavenge side of the pump. I don't recall if the early 3.0's did, or not. But all these issues were related to the change in the relative size of the pump chambers, including the fancy inverted sump screen, and I remember the controversy and all the service bulletins. Porsche even postulated for a while that people were installing the drain plug in the sump screen so that it blocked the scavenge pump pickup. Eventually they came up with a different piston, different spring, and a guide pin for the spring. Something about the piston oscillating and getting stuck I think, or harmonics on the spring or something.

But back to the OP's question, it will do no harm to make the mod, but you should have the correct piston, spring, guide, and plug (I think it changed too?). On the other hand, it is completely unnecessary unless you change the pump to the later style. 2.2's have no oil pressure problems. Actually none of the engines do for normal uses. But when Porsche moved the pressure sensor from the front of the case on top of the tube supplying the main bearing gallery, to the rear of the case feeding out to the cam towers (the end of the line for oil), they sufferered a rash of customer complaints about low oil pressure at idle. It wasn't that the oiling changed, they were just monitoring at a different location where the pressure was lower. And being a "precision" German sportscar, having the idiot light flickering at idle was not good for sales.

[Walt Fricke]

Forsling

To do the upgrade you need the two (identical) new style pistons. You need the new, longer, 930 part number vertical (pressure setting) spring. You need the tubular insert which goes inside this longer spring to keep it from buckling. You should buy two of the newer plugs, with a hex head for much easier tightening. The two aluminum crush rings are the same. And you can reuse either of the old springs on the horizontal emergency relief system - they are still a 901 part.

You may not want to purchase from Pelican, but pretend you have a 3.0 or 3.2, and look at their catalog. Also, take a look at the Porsche parts catalog for either of these two models.

Anyone capable of assembling a 911 engine ought to be able to tap a hole and insert a plug. The trick part is getting the hole started on the new hole you have to drill, because you are drilling at a fairly small angle inside an existing hole. To get a start, you need to use a different tool, like a small, flat ended die grinder bit, to grind a sort of notch into the side of the hole. Then you can get a small drill bit to start perpendicular to the cut surface, and then move on to larger sizes to finish the job.

From the comments, it seems this isn't a must do change, but it is pretty simple, and if you do it yourself, inexpensive, so why not do it?

[Forssling]

Thanks all for your input. And thanks Walt for your detailed instructions.

One thing I wonder though is why I need to change the safety valve piston as well, is this affected by the modification also?

I was originally set to do this, but now I'm more hesitant. I'm not doing the upgrade to pressure fed tensioners. (just safety collars) No oil pump upgrade. It will be an original setup 2.2 T engine. So, from previous posters it seems like the oil by pass mod isn't necessary for my setup. A bit like "not a problem - why fix it".

The only thing I think of is if I want to do any upgrades in the future. Now the engine is split, now is the time to do it. ...or not...

//Jörgen

[E Sully]

I think it is a good modification regardless of pump installed. It prevents excess oil from being released in the sump. This reduces oil in the sump, less to scavenge, less aeration of the oil by the crankshaft.
Good thread here.
oilpump modification

[targa72e]

The factory eventually did this on every case starting with 2.7 line. all later cases have this from factory. It is inexpensive to do. The pistons and springs get changed as part of the upgrade. it keeps extra oil out of the sump and more in the tank.

john

[Walt Fricke]

Forsling - you make a good point about the safety system. It has often been stressed that if you do the pressure mod, but use the old piston, things don't work right at all. If I had a case half handy, I could probably figure out why the holes in the old piston would let oil escape with the new routing. Perhaps the suggestion that Porsche didn't see the need for two parts when one would do explains why they changed the safety piston also. I am inclined to agree that one could just reuse the old parts for that relief function. Would I do it on an engine of mine I had converted to the newer oiling system? Nope, costs are trivial. But good point - if I couldn't find the new stuff for that system, why not use the old?

But like most, I'd do the oil modification if I had the engine apart, need it or not. If nothing else, it is a selling point when that time comes around.

[dannobee]

I would do the mod, too. It'll also help with oil temps and helps keep the oil level in the tank more stable when driving.

[Forssling]

Oooh, you guys are killing me....! Jokes apart, I really appreciate (and trust) your input.

So... if you guys just persuaded me to do the mod, just to make sure, apart from the drilling and plugging, I need:

1 new spring, 1 spring guide
2 new pistons, 2 new seals, 2 new plugs

New spring, guide, piston, seal and plug goes into the pressure relief.
New piston, seal and plug goes into safety relief. (Using old spring and no spring guide)

As said, it's not the cost of these parts, it's the cost of damage I can cause if I do it wrong!!

//Jörgen

[Walt Fricke]

You got it. I think most often, at least here in the States, guys just buy a kit with all this stuff, including the one superfluous spring.

[Forssling]

Thanks Walt! I'll see if there are any kits around here in Europe.

//J

[ParadiseGarage]

Hi all.

I'm the guy helping Jörgen with the engine rebuild. Right most of is over at the machine shop för case savers, oil bypass mod, honing of the cylinders and extraction of a few studs. There are 5 videos of the disassembly. I hope you enjoy!

PS. This rebuild is sort of a budget rebuild so no re-boaring of the cylinders or new pistons. 129 hp from a 2.2 L engine is a fairly moderate figure so the engine will hold up fine. DS.

https://www.youtube.com/watch?v=9yqxnQuDShI&list=PLr3FVX6ongiIgN4PpkLDTkyVHL87WhG7q