PLEASE HELP - what is 911 flywheel sensor pin made of?

[911 Cabrio]

I am rebuilding my 1984 3.2 Carrera Cabriolet and have run into problems.

The sensor pin (part no. 930 102 221 00) on the flywheel was crooked, so, I gave it a very light tap with a hammer which resulted in it breaking off!!

It is small and has a tiny thread and whilst drilling it out I have managed to take too much metal off. I guess it just wasn't my week!

A local engineer says he can redrill and tap the hole and make a new pin with a bigger thread but wants to be sure it is made with the correct metal.

I wondered whether it was chrome vanadium like sockets, etc..........probably not stainless steel as it is attracted to a magnet............any ideas??

Another local chap has said just make it out of mild steel but I have no idea whether this would work or not?

I assume it just needs to break a magnetic field created by the sensors but if mild steel would work why do Porsche make it shiny and very expensive!?!? ($75)

I would rather get it right than have to remove the engine as soon as I have completed the rebuild and should be enjoying driving my "new" toy!!

As I live in New Zealand now it is a real pain to get new parts and the shipping is killing me.............so, I would like to avoid getting a new flywheel if possible!!

Thanks very much for any help offered.

[rick-l]

Originally Posted by 911 Cabrio

Another local chap has said just make it out of mild steel but I have no idea whether this would work or not?

I assume it just needs to break a magnetic field created by the sensors but if mild steel would work why do Porsche make it shiny and very expensive!?!? ($75)

Actually it has to complete a magnetic circuit and I would think mild steel would work fine.

Now can you keep it from rusting and maintain 0.03 +/- 0.01 inches?

[burgermeister]

No answers here ... but thanks for the info on said parts brittleness - I will remember it.

Is the pin magnetic by itself? If it is, there's your answer. Would explain the brittleness also.

If not, I'd have to think any piece of steel would do, but I would be reluctant to reinstall my own engine based on that thought. Are the crank position sensors magnetic in some way? If they are, the piece may just need to be steel to create a pulse. Maybe they wanted something ferromagnetic, but a bit less prone to corrosion than mild steel?

I think any magnetic (but not magnetized) steel moving by a coil would produce an impulse - perhaps some EE will have knowledge rather than fuzzy thoughts. Try emailing user "rwebb" - he seems to be a sciency type.

If you have access to an oscilloscope, you may be able to verify empirically that mild steel would work as well as your leftover pin piece.

It could just be "magnovar" (made by the dilavar company) - the non-rusting extra brittle shiny ferromagnetic alloy that Porsche thought was a great concept at the time. (I made that up, just in case someone is wondering...)

[911 Cabrio]

Rick

Thanks for your response.

I value your view - the only bit that worries me is the use of the word "think" rather than knowing that mild steel would work!!

Would it cause problems if the pin rusted?? Afterall steel with surface rust is still attracted to a magnet.

I really want to know what I am getting into before doing the wrong thing.

Cheers

[911 Cabrio]

Burgermeister

Glad my mistake can serve as a warning to others!! Definitely a bad thing to break off particularly given how awkward it is to get to.

The pin is attracted to a magnet but is not magnetized. Where it is broken off it looks quite glittery and rough textured.

The two crank position sensors are magnetic but not super strong. The one that is on its own (at 12 o'clock) which I think is just for diagnistics is not magnetised.

Would a little suface rust stop the sensor detecting the pin??

Will try to get in touch with rwebb - sounds like a bloke who might know.

It has been years since I have used an oscilloscope, so, if I could find one I honestly wouldn't have a clue what to do with it!!

By the way - I liked your story about "magnovar".......sounded quite plausible!! I hope that was the only bit you were making up!?!?!?

Cheers

[slodave]

Is it possible to use the third sensor - the test sensor at the top of the flywheel that is never used?

Also, wasn't there talk on certain BMW models that used a similar sensor. If so, maybe the BMW route is easier in NZ?

[rick-l]

He is talking about the pin that the sensor (BMW or Porsche) senses as it goes by.
Rust wouldn't affect the magnetic properties and I guess .03 is a lot bigger gap than would be filled by rust.

Any chance that pin is pure iron. Maybe that is why it was so brittle. The relative permeability of Iron is alot more than carbon steel but for that short a piece of the magnetic path I wouldn't think it would make much difference.

Sorry there are a couple more "I think so's".

[slodave]

Originally Posted by rick-l

He is talking about the pin that the sensor (BMW or Porsche) senses as it goes by.

Whoops, read that wrong. Thanks!

What about finding an old scrap flywheel? grab the pin from that.

[rick-l]

Holy cow. A new flywheel for an 84 is $400.

[911 Cabrio]

I can't use a replacement pin because my flywheel now has a bit of a messy hole where I tried and failed to neatly drill out the existing thread.

So, my options are:

- make a new pin with a bigger thread to fit into my existing flywheel once drilled and tapped US$90 if I can find out what metal to use and then be sure new pin will work

- buy a new flywheel from New Zealand, cost over here US$900 equivalent!! Genuine Porsche part.

- buy a new flwheel from the UK and have my parents carry it out in a few months US $350. OEM part.

I have also read that the BMW and Porsche sensors are the same, so, have been trying to see if I can find out what sensor pins BMW use but nothing yet - will keep looking.

I have also seen on Pelican site that the 1987 - 89 Porsche 911 uses a sensor pin that is $6.50 but one for a 1984 911 is $75, so, I am thinking that it must be something pretty special or else a blatant Porsche rip off!!!?!

Keep the opinions coming please!

Thanks all.

[slodave]

Can you make a nice bigger hole, thread, then use a heli-coil or similar technique fit the correct pin?

[KTL]

The exact metallurgy of the original pin is not necessary- just make sure it's magnetic. You guys are over-thinking this.

Similar example to prove my beliefs:

Our '86 BMW 325E was purchased with a no-start condition. Souk discovered that the flywheel sensor set screw was missing. He put in an off-the-shelf metric set screw from the local hardware store and by sheer magic the car started............

Fast forward to 2007. We buy the 325E from Souk and enter it in 24 Hours of LeMons. 4 hours into the race we shut the car off and it won't restart. Never could figure out how to restart it (we did check to see if the set screw went missing again) and finished dead last in the race........ During winter storage, it was discovered that the set screw had come loose again and, while still in place in the flywheel, the gap was bad and the sensor couldn't "see" the set screw. We reset the gap, threadlocked it and all is good now with another new, nothing special set screw that was replaced again. We replaced it again because the previous nothing-special set screw got damaged when it destroyed the sensor.

Fast forward more to Sept. 2008. We redeem ourselves and finish 6th at Detroit-ish 24 Hours of LeMons. Set screw performed flawlessly! That darn set screw and a stupid perceived (but incorrect) relay problem has caused us more problems on the car than I care to admit. Thankfully the car performed nearly flawlessly at the race- broken engine mounts and the resulting cooling system refill were our undoing, otherwise we would have finished 2nd or 3rd.

[3.2 CAB]

I finally got a response from one of the BMW guru's, the pin can just be mild steel. The important thing is to have it secured, and to make sure of the 0.08mm air gap setting after replacing the pin. Good luck!! Tony.

[Kapota]

hello to everyone I got the same problem as 911 cabrio but I my flywheel have standart hole for pin Iam interested what are size(legth) of these pin thaks in advance

[KTL]

Alright, I found this thread Kapota. I'll check the size of the set screw in the 911 flywheel I have and let you know what the size/thread pitch, length of the screw is. What year is your 911 engine we're talking about here? The flywheel I have is from a 87-89 3.2 with the G50 clutch/flywheel package. Reason I need to know is because technically the 84-86 3.2 with 915 clutch/flywheel assembly has a different set screw.

By the way, did you know the spy video game Tom Clancy's Splinter Cell for PlayStation2 takes place in Tbilisi

[MotoSook]

Originally Posted by KTL

Souk discovered that the flywheel sensor set screw was missing. He put in an off-the-shelf metric set screw from the local hardware store and by sheer magic the car started............

Magic? Ha! It was engineering man.

Just install any set screw that will fit the thread. If the thread is boogered rethread it to the next size and install and appropriate set screw. Gap it approx 2 mm go...

[911 Cabrio]

Kapota - my car is a 1984 3.2 Carrera.

The pin head is a solid cylindrical shape with an allen key slot - the cylinder shape measures 5mm across the top and is 6mm tall. I do not know how long the thread is as mine snapped off in the flywheel!! I would have taken a photo but there really isn't much left to look at!

I ended up buying a new flywheel from the UK which came complete with a new pin. By the time I factored in cost of resurfacing flywheel and cutting new thread, etc it seemed the best thing to do at a total cost of £200 to be certain everything worked ok.

A friend of mine reckoned the pin was made of 12 gauge hardened steel or something like that - I have deleted the email of what he actually said?

I believe that the pin for a later car is completely different.

I have no idea about what earlier cars ie 3.0 and earlier.

I hope this helps?

Good luck sorting yours out.

[aquazulu2]

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Threaded Guide Pin, 911 (1984-86)