What size is the fitting for the oil pressure sender, And where to find the extension hose parts Options

[stugray]

I have seen a few other members who have installed the dual sender unit by using an extension hose from the stock fitting location under the dist.

What parts do I need and where do I find them?
I am ordering the dual sender unit from the bird

And while I am at it, I assume that I will only need a 80 PSI sender & gauge for a 4, right (not the 150 PSI)?

Stu

[rwilner]

This is what I used ... Paintball hose

$2.75 Your price may vary.

http://www.discountpaintball.com/Stainless...nch_p_5726.html

This is what I used. The braided stainless acts as a ground, so you don't have to ground the sender separately.

[stugray]

Capn,

What size are the brake line fittings?

IMO - The thread into the case is exactly the same thread.

When I tried to thread in a 1/8" NPT, it got TWO threads in before it stopped, abruptly. Would that hold pressure? - Sure, is it the correct thread - no. If you inspect the threads after trying to thread in a 1/8" NPT, you can visibly SEE the damage to the threads. I had to clean them up a bit before threading in the 10mm.

The 10mm went all the way in until the shoulder bottomed out with zero slop or wiggle.

And I am confident that the seatbelt bolts were a US safety requirement. Did the 914s sold in Europe have the Metric or standard threads on the seatbelts?

I would use the distribution block that you've made there to run a single pole switch, so you don't have to look at the oil light going on at 8-9 psi that the dual pole turns it on at - the gauge seems useless there.

As I stated above, the pressure gauge will be removed once I verify the VDO gauge is "close enough", then I can remove the gauge and plug the hole with the stock pressure switch.

That gauge goes to an accusump. Once I install the accusump, the gauge will be installed there.

With all of the recent talk about VDOs being inaccurate, I wanted an independent pressure reading when I first fire it up.

Stu

[stugray]

The braided stainless acts as a ground, so you don't have to ground the sender separately.

I was actually trying for electrical isolation. That way I can experiment with the grounding to see if it affects the accuracy of the sender unit.

I believe that grounding that sender unit through the chassis is one of the reasons they are inaccurate.
I ran an extra wire to the sender to see if grounding the unit at the gauge will help any.

Stu

[gothspeed]

................

What size are the brake line fittings?

IMO - The thread into the case is exactly the same thread.

When I tried to thread in a 1/8" NPT, it got TWO threads in before it stopped, abruptly. Would that hold pressure? - Sure, is it the correct thread - no. If you inspect the threads after trying to thread in a 1/8" NPT, you can visibly SEE the damage to the threads. I had to clean them up a bit before threading in the 10mm.

The 10mm went all the way in until the shoulder bottomed out with zero slop or wiggle.
...............................

Exactly (IMG:style_emoticons/default/beerchug.gif) !! If we would not use 1/8" NPT into our calipers or brake fittings, we should not use it for the block. Just because the engine block is softer, does not mean we should force and deform the threads in the block by using a 1/8" NPT. (IMG:style_emoticons/default/smash.gif)

[sgetsiv]

I know it's an older thread but I've been working on this oil pressure sender project now for about a week - looking up all sorts of adapters and options. Here's what I know and what the math shows - and I suspect this might help solve the mystery as to why nobody makes a Female M10mm x 1.0 to Male (or female) 1/8" NPT Adapter.

The stock oil pressure switch is definitely a M10mm x 1.0 thread pitch, not tapered (edit / correction - the switch has tapered threads). 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 (edit / correction - unless you have the factory tool).

1/8" NPT has a nominal OD of 10.287mm - ever so slightly larger than the 10mm. But, it has a taper of 1/16" per 1", equivalent to 1.58mm of narrowing in 25.4mm of threads - that means that each thread has a slightly narrower OD at a rate of 0.062mm per thread. 1/8" NPT is also designed to only go on to a maximum of 10 threads.

The 1/8" NPT has a thread pitch of 27 - that's 27 threads per inch. Comparatively, our metric sender has a thread pitch of 1.0mm which is 25.4 threads per inch. Percentage wise, that's a 6% difference. On a per thread basis, we are talking about 2.2 thousandths - 0.0022". Math is 1 / 27 x .06. Note that each thread on the 1/8" NPT is equal to 37 thousandths, 0.0370".

Because the thread pitch is off by 6%, or 0.0022", as we tighten a 1/8" NPT male into the 10mm x 1.0 female, the threads will start to bind quickly giving us a seal. So in theory, we can stick a male 1/8" NPT (grease hose for example) into the female 10mm x1.0 in our engines. THE REASON WE SHOULD NOT DO THIS IS BECAUSE IT IS EASY TO FIND THE MALE 10mm x 1.0 TO FEMALE 1/8" NPT ADAPTER AND WE SHOULD NOT RISK RUINING THE THREADS ON THE ENGINE.

Going the other direction, as in screwing our 10mm x 1.0 oil pressure sender into a 1/8" NPT female fitting (such as a Tee adapter used when splitting off for multiple sending units) is theoretically a tighter fit since the OD of the NPT female narrows to under 10mm at a thread depth of just under 5 threads.

The maximum thread depth of the stock oil pressure sender is about 8 threads, so getting it most of the way into a 1/8" NPT female adapter should create plenty of bind in terms of both diameter and thread pitch.

Or you could just get 4psi pressure sender with 1/8" NPT threads - http://www.summitracing.com/parts/aaf-all99058/overview/

Hope someone finds this useful...

[R8CERX]

I know it's an older thread but I've been working

Hope someone finds this useful...

I have!! Impressed with the the analysis of thread stack up tolerances!!

I would love to learn how you calculated the above - email or pm?

There is lots of good knowledge that I could use for other applications on applying the same analysis to other sizes and thread conversions!!!
(IMG:style_emoticons/default/pray.gif)

[0396]

Great discussion ..

[nathansnathan]

The stock oil pressure switch is definitely a M10mm x 1.0 thread pitch, not tapered.

That is what I thought, based on Scott Lyons of German Supply's article, but like I said, the Factory Workshop Manual says the sender(if not the case?) is a tapered thread.

I was researching this awhile back and came across a German word (that I now forget) for the practice of creating a seal by threading a straight thread into a tapered hole (or is it the other way...?) That may be what the factory had going on. If so, the tapered sender seems like an improvement, if the factory one was indeed straight threaded.

There being no gasket in the gasket set to seal a straight thread sender, in a straight-threaded hole, like the German Supply article talks about, makes it doubtful to me that it was like that from the factory.

[sgetsiv]

It's all just basic math. It probably helps to have a degree in engineering - mine is in electrical engineering modified with computer science. The key is to just do the ratios and remember that 1" = 25.4mm.

I forgot to mention in my previous post that another solution might be to cut the 1/8" NPT Female with a 10mm x 1.0 tap. The thread itself of 1/8" NPT from peak to trough is 32 thousandths of an inch - you can calculate this by taking the tangent (ratio of rise over run) for half the distance between threads and threads are cut at 60 degrees.

By the time we got down 8 threads, the error would be around 16 thousandths and with distance between threads of 37 thousandths - that's not good. But the 1/8" NPT has a taper of 18 thousandths so the time we get down 8 threads, we are getting nearly complete thread coverage.

Here's a drawing I through together to illustrate:


I guess it's obvious as well that forcing a 10mm x 1.0 oil pressure sender into a 1/8" NPT female adapter would bind up pretty bad after a depth of 3 threads. Therefore, my recommendation would be to cut the female NPT adapter with a 10mm x 1.0 tap. That's what I'm planning to do.

[sgetsiv]

Since the case is aluminum, it's soft enough that the harder threads of the sender will slightly cut the threads on the case. I would bet that the factory tapered the M10 x 1.0 for this reason to create a stronger seal. And I would bet that after a few times pulling and installing the sensor, that the case has been essentially tapped for M10 x 1.0 straight thread.

The German word for tapered thread is "kegliges gewinde" and indicated by a K.

[gothspeed]

+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. (IMG:style_emoticons/default/popcorn[1].gif)

[stugray]

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

[nathansnathan]

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

DIN DIN 158-1: Metric taper external and mating parallel internal screw threads - Dimensions, tolerances and inspection
Publication Date: Jun 1, 1997
SDO: DIN: Deutsches Institut für Normung e. V.
DOD Adopted ANSI Approved Approved
Scope and field of application

This standard specifies profiles, dimensions and methods of verification for general purpose metric taper external threads intended to be mated with parallel internal threads with a basic profile as specified in ISO/DIS 68-1

Taper external threads as specified in this standard are intended for self-sealing joints, such as those employed on pipe plugs, compression couplings and lubricating nipples. They can be used in all cases where a parallel threaded joint with washer is unsatisfactory for technical or economic reasons.

For fluids such as oils, other liquids and gases, no thread sealants are required for joints where the nominal size is small. For joints of greater nominal size, it is recommended that sealants be applied, since the leaktightness of such joints decreases as the diameter increases.

A short design taper external thread has been specified along with the standard design both to be mated with general purpose IS0 metric parallel internal threads of tolerance class 4H for the pitch diameter and 5H for the minor diameter (as in ISO/DIS 965-1).

Aussengewinde
metrisches Gewinde

[Cap'n Krusty]

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

[stugray]

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.

[Cap'n Krusty]

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

[gothspeed]

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.

+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.

[stugray]

I suggest you read Post #48, above, and pay particular attention to the highlighted sentence in the illustration.

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.

[0396]

So I followed the above advice and got the 6" grease gun hose at autozone.
I still installed the 10mm to 1/8NPT adapter. It threads into the case perfectly and the hose threads into that like it should.
And I used some brass...
Anyway, I wanted to find a solid place to mount it where I could also thread on a mechanical gauge when I want to, and remove it easily.

Here is my solution: One hole drilled in fan shroud and some scrap aluminum I had laying around.

The mount that holds the brass tee is somewhat shock isolated with rubber.
I can easily unscrew the mech gauge and plug the port.

(IMG:http://www.914world.com/bbs2/uploads_offsite/i366.photobucket.com-10819-1367906573.1.jpg)

(IMG:http://www.914world.com/bbs2/uploads_offsite/i366.photobucket.com-10819-1367906573.2.jpg)

It doesnt interfere with the coil position either.
Thanks for the tips.

Stu

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

Thanks

[stugray]

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