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

1/8" NPT Get the hose from your FLAPS. I use a grease gun hose. Remember, you MUST ground the sending unit! I put a ground wire under the clamp and run it to a bolt on the fan housing. Sender must match the gauge.

The Cap'n

Thanks.



I am buying both a sender and a gauge.
So I believe that I will never see greater than 80 PSI on one of these engines?

Stu

Yep, 80 psi is what you need and the Cap'n is spot on as usual with the other details...

I am trying out a short brass pipe nipple and t arrangement. Has to get through the tin, not get in the way, and be removable. I ended up soldering. Engine goes in tommorow. I am bone tired but will add pics then.

the brass pipe is not as good as the grease hose.

the brass can work harden and in theory crack at the base of the thread.

Stu, which pump is on it ?
also are you using the high pressure pistons?

I've used both 80 and 150psi
if a big pump, with high pressure pistons you may need the 150 psi set up.

stock pump & piston.

I was hoping whatever gauge setup I got it would still work with the better pump when I upgrade.
I ordered the 80 PSI just about an hour ago.

Stu

80 psi is good for stock pump.

I'm not a fan of the 1/8 NTP since that's not the correct thread.
I use a brake hose as an extender.

That's interesting. Do you have a photo? Which brake lines? Hard, soft, etc.. How did you mount yours?

Air hose from a paint ball gun also is correct, and looks better.

rich

If 1/8" NPT is not the correct thread, what is?

I would find it odd for a all metric engine to have a US pipe thread on it intentionally. It is probably one of those cases where the thread is so close that it works fine. Kind of like the seatbelt bolts....
I will just go with the 1/8" MPT.

Thanks

Stu

+1 ... Yes, the 1/8 NPT is not the correct thread, it is only 'close enough' to capture a few threads and deform the rest.

A 10mm x 1.0 thread pitch will engage threads all the way down and then you can use a copper sealing washer.

Thanks all.

So in other words...."Same as the brake line fitting thread".

However I see that the Hella Pressure switch that was in the engine previously is definitely a tapered thread.
Is there such a thing as a Metric 10mm NPT?

Stu

EDIT: Just found this: https://www.pegasusautoracing.com/productde...ls.asp?RecID=55

Metric Pressure Gauge Adapters, M10x1.0 to 1/8" NPT
Too bad you have to get the $46 kit when you just need the one...

Whatever you do, do NOT use brass tubing. I was at the track this weekend when a race-prepped 911 that had a brass "T" cracked that fitting and sprayed oil everywhere. Not only did he risk dropping oil all over the track, but he could have lost that engine over a $2 part. I don't think people realize how fast oil pours out at 40+ psi.

As brant said, they stress harden and crack. We were able to remove the T and simply thread the pressure switch back into it's original hole and had him back on the track in several minutes. The grease hose and grounding wire works great. You can use a closed, or "blind" grommet to cover up the large hole left in the tin.

The aftermarket sender for the gauge is also kind of large and a bit heavy. If you put that up on top of a pipe, you've got a nice bit of leverage to help wiggle the pipe around and damage the threaded hole or even crack the boss on the case. Not good.

The threads are tapered pipe threads. I'll have to look into the brake hose ends; M10 tapered pipe threads are otherwise difficult to find in the US. 1/8" NPT seems to work pretty well...

BTW, the seat belt threads are in inch size, I think due to some DOT requirements.

--DD

At the risk of asking a dumb question why not just trim the tin shroud so the larger sender will fit?

David

The original oil pressure switch is 1/8" NPT. What makes you think anything else would be correct? The hole in the case is tapered, so threading in a brake hose doesn't assure a good seal, and you'd need a copper gasket on a flanged line. (German brake lines use the taper on the tip to make the seal, NOT the threads. You've introduced a number of BAD things here. Possible (even likely) thread damage to the case, leaks, a gasket to reduce the possibility of leaks, and another junction to deal with farther down the line. For what? The KISS rule applies here ......................

The Cap'n

I believe it also interferes with the distributor.

--DD

I've got a dual pole sender with the hose fitting that came off my car recently. all works great. it's listed in the classifieds if you want to get it all turnkey for cheap.

I was hoping to sell with the gauges but will split if you want it.

Captain, I thought the same until I checked.

HARBOR FREIGHT has an oil pressure set with all the adapters. There is a tapered 10x1mm to 1/8 NTP adapter in the set. The entire set goes for a song on sale.

I threaded a 10X1.0 brake line fitting all the way in with zero wobble.
That leads me to believe it truly IS a metric thread.
I am sure the 1/8" NPT works fine, just not the original.

I am waiting to get my sender unit before I buy any fittings.
The fact that someone makes this:
https://www.pegasusautoracing.com/productde....asp?RecID=1832

Leads me to believe that at least SOME euro cars have metric pressure ports.
Who honestly believes that German engineers in the 70s would even consider putting a US standard thread in their engine designs?

Stu

I've always used the same method as the Cap'n.
Works perfect everytime.

grease hose..
3$

I've used them on 10 different motors
works perfectly
doesn't leak


KISS

its not a porsche part
but I'm not a concours guy..
its a perfect race car part.

1/8" NPT and 10mm x 1 TAPERED threads are so close most folks, including pipe thread specialists, could NEVER tell the difference.

The Cap'n

How do you tighten it down with the hose? Wrench doesn't fit

Carefully.

You can modify a wrench so that it fits, if you can weld. You can also install the hose with the engine tin off. I think that's what I did last time.

--DD

The grease hose fit perfectly.
I also did a test fit of the hose before installing the tin for the final time.

It seems that you can install it with the tin in place and some long needle nose.
I also figured two ways that you could make a special tool:
Cut a slot in a cheap 12mm deep well socket, or cut the end off of a 12mm box end wrench and weld it to a 1/4" socket extension (as Dave mentions above).

I wanted to be sure you could do a repair to the hose without removing the tin.
Seems easy enough with the engine on a stand, different story with the engine in the car.

I am still debating getting the adapter because that would extend the hole up an extra ~3/4".

But otherwise the grease gun hose is the perfect solution.

Thanks

Stu

A friend had his dual sender on a 1/8" pipe for years and then one day CRACK! oil all over the place! Fortunately it happened in a parking lot and he caught it in seconds!

Since there are 28 threads per inch in 1/8 npt and there are 25.4 mm in an inch, it's really not that close a match.

If the sender boss is tapered (which from my research it is not) it would be m10x1.0K. The K means keg which is a german way to denominate tapered threads. There is some confusion on vdo's part labelling senders m10x1 and leaving the k off though despite that they are tapered, though.

If you look up the part numbers for the sensors that were originally installed and check the threads, they aren't tapered. There is some info in this old shoptalk forums thread
http://www.shoptalkforums.com/viewtopic.php?f=15&t=82113

The relocating hose is the way to go since the dual pole sender is so heavy - ideally plumbed to a T to a stock sender since the dual pole triggers the idiot light too soon.

27

You're right, I was thinking 1/8" bsp, which is 28, npt is 27.

Still though, 1/27" is .037", and it is off by 50% more than that.

The sender only goes in like half an inch, so the difference is halved - but the difference is huge, one of the threads will be off by ~27 thousandths, which is a mile by machinist's standards.

1/8 npt will work but it is not right like using 7/16-20 for seatbelt bolts, being within within .005" of their metric counterparts.

This is what I used ... Paintball hose

$2.75 Your price may vary.

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

Click to view attachment

+1 ...... when I compared the 1/8" NPT to the stock pressure sender, the 1/8 NPT no longer matched past the 2nd or 3rd thread. There was no way I was going to 'force' a 1/8" NPT into my fresh 2056 block. That was when I began my search for the correct thread pitch.

Nathan is correct that "K" is the tapered version of the metric 10 X 1.0. Good find!

I also agree the flex hose 'instead' of a solid pipe is the way to go.

I like using the grease hose and I've never experienced a problem, but running a 1/8" NPT tap into the case might be a big plus in terms of good thread engagement and sealing.
It would be easy with the case apart, a bit more difficult with a complete engine out of the car, and not a sensible thing to do in the car.

Funny, I was at Harbor Freight today and looked at a "Metric Tap & Die set".

It just happened to also have a 1/8" NPT tap.

Strange coincidence?

Stu

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.





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

Stu

I saw yesterday that the Factory Service Manual, they specifically call the sender hole out as having tapered threads and not to tighten it too much so you don't crack the case.

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.

Not too bad an install, no need for dampening the sensor though, and fixing a hole made in a fan shroud is a tall order since it's hard to weld magnesium. I have mine mounted to a bracket held by a case through bolt on top of the engine.

You're speaking of those same engineers who specified SAE equivalent bolts and nuts for seat belt mounting points, right? BTW, BMW used a metric threaded oil pressure sender, but it's 10mm and a straight coarse thread.

The Cap'n

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

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?



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

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

Exactly !! 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.

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...

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!!!

Great discussion ..

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.

Click to view attachment

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:
Click to view attachment

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.

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.