Flywheel magnet

[av8r4aa]

Been trying to figure out why my M6 won't start.
Been through the gamut and asking if anyone has ever
heard or actually replaced the magnets in the flywheel.

Reason I ask is that my mechanic has replaced both sensors
and one came out a little scratched.

Both new sensors in place but questioning the actual magnet
in the flywheel. Do these ever come loose and fall out?
How are they kept in place?

[alrivers]

i actually had that problem with my 6er. My reference sensor (magnet that you're talking about that goes to the flywheel) failed. It only took me about 2 weeks to figure that one out because it was actually a series of issues: starter motor, ignition switch and ref sensor. After replacing the sensor, it started right up!

If you look under the car at the trasmission bell housing, you'll see a small goldish (on mine at least) looking plate. That plate protects two sensors (if i remember correctly the bottom is the reference one) that are just bolted on. The wires lead up behind the steering box and up against the firewall to the senders on the top of the engine.

*edit* mine didn't fall out. ;)

[av8r4aa]

How do you replace it?

[alpinacsi]

I don't believe the flywheel has a magnet but actually has a tab that the reference sensor (magnet) reads. You should have an alum pan at the back of the oil pan that you can remove and inspect the flywheel.

So the ends of the new reference sensors are banged up or just scratched on the sides from pulling it thru the sensor port? I have seen pieces of the T/O bearing break off and damage the sensors but I have not seen the issue so much with the tab on the M6 (seems to be fairly common on some of the eta engines).

[CW6er]

The Speed Sensor reads the teeth of the flywheel, and the Reference Sensor reads a single metal dowel pin inserted in the flywheel. I've read that these have come out. The Bentley says that it is visible through the bell housing timing hole (Pg. 8-11).

Also, Double check that the sensors got in the right holes.

The sensor connected to the black plug goes in the bell housing hole marked "D" (Speed Sensor)

The sensor connected to the Gray plug goes in the bell housing hole marked "B" (Reference Sensor)

[Seeker]

I took a look at my 633 Flywheel and couldnt seem to locate the metal dowel pin.

I thought it was a little magnet that the sensors read too.. and I thought there were more than one.

Guess I've assumed too much on how those sensors actually work.. I thought they were little coils that could sense a magnet fly within its sensing range..

[av8r4aa]

My mechanic has replaced both sensors,
neither did very well on the Bentley check.

One of the two he removed he said had a crack and was
scarred up. I will need to have him do a visual on the pin.

If it is missing then I hope he can replace it without a lot of
expense.

Thanks everybody for adding their input and knowledge.

[JRanmann]

You should have an alum pan at the back of the oil pan that you can remove and inspect the flywheel. A good point and an easy to slowly turn the crank and inspect from there...it is a magnet insert IIRC and if no other souce of the issue is found you might have to invest in a new clutch too!

It's NEVER easy with these cars ... except in-between each crisis that rears it's ugly head...good luck!

[oxen]

i have had this problem. had a fly wheel machined , got the car back together here in the shop an it wouldn't start. so i looked in a found i was missing a little some thing.

figured it was the fly wheel since the car had ran before i took out he trans an replaced the clutch.

i could see it leading to some d.i time if it happened when the car hadn't been taken apart. i probley would have tested the main relay the crank sensors an the ecu . an tested the wire harness pin out . that would be a few hrs.

[johnnye23]

You can remove the cover and take a screwdriver and spin the flywheel a couple teeth at a time and look to see if the pin is installed. I just diagnosed a no start on a 528e and indeed the tab was missing,I found the flywheel was cracked and caused the pin to break off. In my case I will have to replace the flywheel not sure on the M6 flywheel. I am going to try and Pm you a picture to show the pin.

[CW6er]

I am going to try and Pm you a picture to show the pin.

PM? :shifty

Post it here, we all want to see! :cool

[alpinacsi]

Just surfaced this one this morning. The tab is not a magnet. Tab is at the 2:00 position on first pic.

[JRanmann]

The tab is not a magnetThanks as my recollection was foggy but it is simply a conductive pin, moving thru the sensor's Electrical 'field' I suppose that activates the pulse...or can it be thought of as an inductive coil setup in miniature and the action also powers the pulse or is that off the harness lead and always present at the flywheel? Would like to know as it's ingenious if it only needs field current to work.

I assumed it was electrical magnetism that passes between the sensor's field and the pin itself as the pin likely becomes magnetized over time.

Here's a good outline, including Motronic basic and Motronic 1.1 which may be relevant...for the e28 based sixers here that wish to delve into this more deeply...

http://www.hiperformancestore.com/Motronic.htm

[av8r4aa]

Thanks Everyone,
Trying to get the M6 to move under its own power.
I was sent the ECU. I open it up and inspected it with a 10 power
glass. I removed the chip, looked at it, very lightly cleaned the
contacts. I closed it up and a local M6 friend was OVERLY Generous
to let me try my suspect computer in his car.

The damn thing went like a scalded ape!

We reinstalled his original ECU.

I did re flow every solder joint and cleaned the board to a operating room degree.

I might have had a micro corrosion on my chip and cleaning it fixed the fool thing.


I then sent my ECU back
to California to be reinstalled and tried again.

I am fishing about the flywheel tab because everything else is checking
out.
I will need to see if my "frequent flying" ECU is going to start my M6
or to look elsewhere for a problem.

As with these cars .............." It's always something"

I guess that is why we love them so. :buttrock

[JRanmann]

As with these cars .............." It's always something" one switch or another sensor?

lol!

Cheers Greg!