+1 ....... as you mentioned, there is a .0022" delta in thread pitch between the NPT and the 10mm x 1.0 ..... 'per thread' ...... so unless someone is only planning on 3 threads of engagement, it does not take long to stack .0022" over several turns before it becomes a problem.

In my experience, it only took about 2 finger tension turns, for me to realize there was something wrong. The factory may have specified a tapered thread in this application but it certainly was not an NPT thread. These old cases already have enough problems to deal with, without us purposely creating more of them.

sgetsiv - thank you for confirming my suspicion.

Again "WHY would german engineers make an entire engine with Metric threads and then in only one place put in SAE threads?"

Ask this question: "What is the thread of the CHT?"

And dont go playing the "engineer" card to much, it tends to piss off the natives. (I have EE with 20 years in Aerospace).

Good job on the investigative work. I agree wholeheartedly with your conclusion.

Stu

I found the link I was thinking of, not a word, but a standard is what it was, from the Deutsches Institut für Normung e. V..

DIN 158-1
mating tapered external threads to parallel internal screw threads.

http://engineers.ihs.com/document/abstract/ZSMXJBAAAAAAAAAA

The stock oil pressure switch is definitely a M10mm x 1.0 thread pitch, not tapered. The engine case is tapped near the distributor for an M10mm x 1.0, not a 1/8" NPT. And yes, it takes a narrow wall deep 24mm socket to remove the stock sensor from the case.
Hope someone finds this useful...
[/quote]

In this case, you are ABSOLUTELY wrong. The sender is tapered, and it's READILY VISIBLE to the naked eye. Senders that are not tapered come with a captive sealing washer. Furthermore, I have been installing switches and accessories with 1/8 NPT fittings into both aluminum and mag Porsche cases for more than 40 years (and that's only the time I've spent as a professional wrench, in addition to the other 15 years or so before I became employed as a mechanic) and have yet to run across a case of thread damage caused by such installation. BTW, if you have the factory tool, you don't need that deep well socket, either.

The Cap'n

Cap'n,

Would you please explain how I can thread a 10mm X 1.0 threaded adapter WITH NO BINDING into: The oil pressure sensor port, the CHT port, and the brakes absolutely perfectly?

When I try to thread in a NPT it binds after only three threads.

The adapter (10mmX1.0 to NPT) worked perfectly and does not leak.

I think the only debate here is IF the 10mmX1.0 on the sender units are tapered or not.
I could believe the taper to help with electrical contact.

I think that we have determined that the NPT threaded sensor works fine, but was not the original design ( based on sgetsiv's measurements)

Just because someone has been doing it wrong for 40 years and it works does not make it correct, just good enough.

The guy I race with every other weekend that builds RSRs for a living laughed at the thought that there was a SAE thread anywhere on a Porsche engine when I mentioned it.

I suggest you read Post #48, above, and pay particular attention to the highlighted sentence in the illustration. Please note the illustration is a copy of a page in the factory workshop manual. Granted, there are errors here and there in the manual, one being the rear brake venting clearance, but this isn't one of those errors. The hole is tapered, the switch is tapered, and I believe my practical (and yes, anecdotal) experience is good in play here. While the 10mm taper and the 1/8 NPT taper are not EXACTLY the same, they're plenty close enough to fit, to seal, and don't cause damage to the parent metal. Brake line fittings (and 356/912 oil line fittings) are 10mm fine straight thread. In the case of European bubble flare brake fittings, the seal is made by the flare, not the threads. In the case of brake line banjo fittings, the seal is provided by copper washers. In the case of 356/912 oil lines, the ferrule does the sealing. If you use a 10mm fine thread fitting in the tapered hole for the oil pressure switch, you will need a sealing washer to affect an leak proof connection. The factory does not provide for such a seal in this case, even though it is common in other oil pressure switch applications in both Porsche and VW/Audi Group applications. I rest my case, as I'm tired of beating this poor horse. You can choose to do what is both practical and works, or screw around indefinitely posing engineer excuses why it can't/won't while I put miles on my car. Same goes for the seat belt anchor bolts. Remember, it's the job of the wrench/mechanic/tech to make what the engineers design actually work in real life!

The Cap'n

+1000 ....... doing something wrong for 40 years does not make it ok.

BTW every 1/8 NPT male thread fitting I have seen stuffed into a 10 mm x 1.0 tapered or not ..... was 'forced in' and numerous times upon removal I have noticed metal shavings from the 10mm side (aluminum or magnesium depending on what it was made of) ....... all this good information on this 'thread pitch difference', confirms the thread deformations and particulates/shavings I have seen in those interfaces, on many motors throughout the years.

I did.
pay particular attention to: "The oil pressure switch is sealed by means of the tapered threads"
In my opinion that means that the threads of the part being screwed IN is tapered. That makes perfect sense if the part has to make electrical contact upon installation.

Nowhere does it say that the threads on either side are SAE OR that the threads in the case are tapered.
If the threads in the case were tapered then I could not thread in a 10mmX1.0 fitting without it binding.

And Yes you have to use a crush washer if you install the 10mmX1.0 to 1/8"NPT adapter into the case.

Very cool, where did you buy the gage , T, and sender? Harbor freight?

Thanks

Gauge, jegs or pegassus.
It is for an accusump oil resivoir.
Turns out it is actually meant to read the air pressure on the "dry side" of the accusump, but seems to work fine.
I will remove it before racing, but I wanted an independent gauge when I first primed the engine.

T & adapters - Ace hardware.

Adapter into the case Pegasus
sender - Pelican

Looks good!!