Darwantae951

Bingo!

Tom M'Guinn

Interesting. All the ones I've measures are the same height mating surface to mating surface. I wonder if Porsche just started tapping the threads deeper on the later housings to accommodate the extra threads in the new OPRV. If I understand Dare's posts correctly his pictures were of the oprv screwed into the housing when the housing was not on the block -- suggesting it just ran out of threads in the old housing. From Porsche's perspective, that would make the new housings backward compatible so no need for a new part number, so makes some sense. Has anyone measured the thread depth in the old v new?

Thom

Jay, thanks for that.

If the later style OPRV doesn't thread as deep as required into the housing, then this may cause an internal leak and possibly result in a lower oil pressure? Is this correct?

In terms of configuration management, it is nowadays generally agreed that a part has to be 100% interchangeable with all parts with which it is mounted, in order to keep the same part number.
If during one step of the redesign one feature results in at least one of the surrounding part not working with the redesigned part, then its part number should be changed.

As far as I gather from the Porsche part numbering system, the two last digits evolve with minor modifications that do not impact the interchangeability.
I'm certainly missing other details, but in the current case, I find it odd that the part number was not changed, even if adding some threads in the housing has more to do with the industrial/machining process than the actual function(s) of the housing.

(this is the reason why I'm sticking to an old version of PET - I like the possibility to spot "old" part numbers on the sketches that do not necessarily show up on more recent versions and on the .pdf)

Dare

I believe this is right. The threads of unmodified late OPRV bottomed out in the bore of the early filter housing. If I remember correctly, when I looked closely at it, it was clear that the threads in the bore could have been run deeper.

Its unclear to me how much difference a few threads would make (e.g. if you just stacked up another washer). But the whole design seems so touchy here I didn't want to chance it.

BTW, in case anyone is interested, here a picture comparing the threaded sections from the 3-piece OPRV (left) and the 87+ OPRV (right):

Thom

So I just looked on the car and even though I'm using a housing that comes from an '86 and a late OPRV, it would seem that there was enough thread in the housing to screw the OPRV all the way.

I also found this other picture in my archives.

As I can't remember much about this phase of the assembly, I may indeed have not run through this issue.

Thanks everyone for your experience with this. Sorry Tom for deviating from your build thread somehow.

Tom M'Guinn

No worries about the thread -- good info. I will have to look at some housings and report back. If anyone has a housing handy now, post up the casting number, height from mating surface to mating surface, and the depth of the threads in the port.

lart951

Here is a comparison of the three different OPRV's

reno808

dam dude

Chris White

One of the key differences between the 3 piece ‘system’ and the later system is that the blocks that used the 3 piece OPRV had a steel liner in the bore. That was there because of the steel piston that moved in/out to regulate the amount of oil being bypassed to maintain pressure.

I suspect that the newer style OPRV bottoms out against the steel sleeve before the sealing washer.

Tom M'Guinn

If you look at Dare's post #1 and #3 in his thread, he seems to be saying the one piece would not screw in all the way, even with the housing sitting on the bench -- suggesting the threads in the housing are just too shallow. That theory is also supported by those who have success shaving off the last few rows of threads on the 1-piece OPRVs. Eventually here I'll pull out my old housings and see if I can confirm...

Dare

That's right. I tried that test exactly, and the threaded section would bind in the hole before it would seat on the washer. Confused the hell out of me until I saw a picture of the retrofit valve with the turned threads.

Chris White

I have a ¾” drive air impact gun that takes care of minor annoyance like that. 1200ft lbs. It puts the fear of god into aluminum parts!

I can’t say that I have tried to install a late OPRV in an early housing, For most performance builds I replace the OPRV if there is any question. It does not take much to screw up the regulator – a small piece of bearing from a failed engine will jamb it up.