Cam sprocket magnet - CSI

[ChrisWhewell]

The scene of the crime, note the circular abrasion marks on the face of the sensor.  The black plastic housing my magnet was contained in at one time, remains on my cam sprocket.   The magnet's location is unknown.   The reason for the failure was the plastic that held the magnet in place, wearing off by continued contact with the sensor face. 

 

Now that I have a new magnet, I can measure the oem dimensions of the replacement part.  Next, I obtain a barved press-in plug of proper dimension, and affix my own magnet to it in permanent fashion.   Fortunately, magnet technology has advanced since 1990, and powerful rare earth magnets are available cheap, at essentially any dimension one wants.  I may alternatively begin with a screw in plug and put my magnet in it, then just screw the plastic plug in the 1/2" hole where the oem magnet was supposed to go, from the front side.  JB weld is permissible.

The beauty of stronger modern magnets is they can be located at a little more distance away from the sensor and still work fine due to their higher field strength.   I'll keep ya all posted, but once I get the right config, putting my new contrivance in that hole should be a 5 minute job.  The hardest part will be finding a polymeric plug of an appropriate polymer composition that withstands gasoline and oil and thermal cycling.  Plastic is easy to machine, esp. by hand

[Ronnie]

I like a man that goes against the grain and does things his own way. Damn the torpedoes. Full speed ahead!

 

If you decide to come down to earth and do the magnet replacement the conventional way, new magnets can be found here (among other places) and instructions on how to install it can be found here. Thanks to Padgett for working out this procedure many years ago.

Edited September 29, 2015 by Ronnie (see edit history)

[Guest my3buicks]

Having just done this job in the Driftwood couple a few months ago, I wouldn't even consider doing it any other way than Padgett"s procedure.  It worked perfectly.  As a side not, I found that laying a sanding mouse upside down (I held it that way between my knees) and then using that to perfectly and smoothly grind the lip off the plastic magnet cover worked perfectly.  I also found that a deep well socket the size of the plastic protector then stuffed with paper so that the magnet could not slip back into the socket worked wonders to put the magnet in place once the bonding material is applied.

[ChrisWhewell]

Trimming the brim and using metallized epoxy is a viable option, I've seen nothing but good feedback on that and am grateful to Mr. Padgett for his intellect.  The question in my mind is.... if a young GM engineer can make a magnet housing that inserts to be securingly engaged from side A of a sprocket, then, can a magnet housing not also be made of appropriate dimension that inserts to be held securingly engaged with the sprocket from its side B ?   Of course.  Second question... would I be willing to pay $30 for such a contrivance, I could just pop into place ?   I would.  I'd drop the 30 bucks, walk out in the garage right now, pop it in and be done with it.  Might even carry a spare.  Not far up the road is a genius machinst with a full shop, he emigrated to Texas 30 years ago from Detroit and makes parts for NASA, among others.   The question is, how many should we make ?

Edited September 29, 2015 by Reattitude (see edit history)

[drtidmore]

I'd be in for a couple!  I did do the padgett fix on my '89 a year or so ago and so far NO issues, but if a securely locking front inserting replacement with a stronger single vs multiple magnets was an option it would be something of a no brainer.

Edited September 30, 2015 by drtidmore (see edit history)

[jonlabree]

Great Idea. I am surprised no one has thought of it before. I appears to be doable.

[Guest my3buicks]

thinking out loud, wonder if there is a reason that multiple magnets were used to begin with and not one larger one?  Could the polarity of the magnets in the "hat" be staggered? 2 going one way, 2 the other? 

[drtidmore]

thinking out loud, wonder if there is a reason that multiple magnets were used to begin with and not one larger one?  Could the polarity of the magnets in the "hat" be staggered? 2 going one way, 2 the other? 

 

Given the relatively small spacing between the magnets in the GM design, the relatively LARGE distance between the interrupter and the sensor, an alternating magnetic field due to reversed polarity of the 4 magnets is pretty unlikely.  The biggest strike against this possibility is that the interrupter (magnet) itself inserts with NO particular rotational alignment into the cam sprocket.  It is more likely that GM was working the old strategy in which 4 small cheap magnet provided the needed magnetic flux density at a lower cost than a simpler higher cost rare earth single magnet and it provided some redundancy so as to ensure the 50,000 mile emissions warranty requirement.  A simpler single induced voltage pulse in the sensor for every sweep of the interrupter magnet allows for a relatively large signal with a relatively long duration in which signal processing can more easily present a precise trigger signal to the ICM and ECM.  

[Ronnie]

Just a little food for thought... Maybe the individual magnets makes the magnetic field more directional? Since the magnet is used for timing the injector opening pulse with the opening of the intake valve, would a solid magnet of greater magnetic strength trigger the sensor earlier and cause the timing of the injector pulse to be off? I don't  know that it would make a difference but it seems it could happen.

 

"the interrupter (magnet) itself inserts with NO particular rotational alignment into the cam sprocket."

Along these same lines, you can insert the magnet backwards and the sensor will not work. I remember someone inserting the magnet into the sprocket backwards after grinding off the tophat and it didn't trigger the sensor. Could the sensor have a magnet in it that requires the polarity of the magnetic fields of both  magnets to be correct?

 

Stubborn e041
 

[drtidmore]

 

 

 

"the interrupter (magnet) itself inserts with NO particular rotational alignment into the cam sprocket."

Along these same lines, you can insert the magnet backwards and the sensor will not work. I remember someone inserting the magnet into the sprocket backwards after grinding off the tophat and it didn't trigger the sensor. Could the sensor have a magnet in it that requires the polarity of the magnetic fields of both  magnets to be correct?

 

 

When you swap the polarity of the magnet, you also swap the polarity of the voltage pulse in the sensor!  The circuits fed by the cam sensor are expecting a pulse of a minimum amplitude and a specific polarity, so you reverse the magnet, you reverse the sensor output polarity, NO signal detected. There is nothing magic about this, just simple basic EE 101 stuff.  

 

While it does seem at times that GM makes things overly complicated, the auto industry seldom, if ever, go for anything more than the absolute simplest solution.  The cam sensor does NOT actually time the injector opening but rather it syncs the sequence of the injector firing to when top dead center #1 cylinder occurs which when added to the dual crank sensor inputs gives the system the knowledge of when to actually fire each injector.  The output of the dual crank sensor alone gives one in six odds of getting it right, so that alone is not sufficient.  Remember the 3800 is NOT a direct injection engine, but rather the injectors sit above the intake valve of each cylinder sharing the intake manifold with the rest of the injectors. When any intake valve opens the entire intake system feeds that opening but if the injector sitting directly above the opening intake valve IS the one firing, it is MUCH more precise. So if the injector sequence is off, the engine still runs more or less like an old carburetor or throttle body single injector design...not optimal, not within emissions standards, but it runs pretty damn well.  Once the injection system has the cam signal, the actual opening of any injector is timed by the dual input crank sensor which uses two different pulse trains giving a quadrature signal allowing far more precise timing that any single sensor. The whole reason behind sequential port fuel injection was to be able to go closed loop with the oxygen sensor and adjust the fuel mixture on a cylinder by cylinder basis to meet not only emissions standards but to improve fuel economy.  

 

I was working in TI Opto-electonics engineering in the early days of GM's effort to move away from the old distributer setup. We were trying to see if opto-electonics could provide a way out of the quagmire GM was facing.  Early efforts attempted to use the existing distributer mechanical setup but with electronics rather than breaker points and this was an improvement, but the issue was several degrees of slop between the actual top dead center #1 and the distributer due to the timing chain and gearing to the distributer.    GM knew even in those early days that they would need sub 1 degree accuracy in the timing of the injection and firing of the spark plug to meet ever increasing emission standards. Reading directly off the cam shaft, which is very accurate, is a hostile environment of heat and oil and sensors are difficult to maintain in those conditions.  Direct cam shaft reading sensors were tried but the failure rate was found to fall outside the 50,000 mile no maintenance requirement of all emissions related systems.  Just moving the cam sensor the front of the engine was a vast improvement to the longevity of the cam sensor with no loss of accuracy.   FYI, opto-electronics were a dead end as far as emissions control system were concerned, but it was an interesting insight into the problem.  That effort did lead to GM deciding to use opto-electronics in other areas such as the move to a digital cruise control....but that is whole other story.

Edited September 30, 2015 by drtidmore (see edit history)

[padgett]

OK, GM needed something quick and easy so inserting the magnet from the back until the arms locked in place was fast & nothing had to dry asy before the sprocket was assembed to the cam. Not so later and generally later you have time for the epoxy to set. There is a JB Quik that sets in 5 minutes but I've never tried that.

 

Now my notes say to keep the arms intact because they make sure it goes in the right way and the right depth.

 

Don't forget that GM did away with the cam sensor entirly shorly after the Reatta or they might have used something different.

 

ps my 88 is still running fine with the prototype done over a decade ago.

[Machiner 55]

"Not far up the road is a genius machinst with a full shop, he emigrated to Texas 30 years ago from Detroit and makes parts for NASA, among others.   The question is, how many should we make ?"

 

No, The real question is, Is he adopting and will he pay for relocation?

 

Seriously though, it's a wonder I hadn't thought about this in the way you have. Within minutes of you suggestion, I conjured an image and a method of making these. Mostly, all one would need was a decent small lathe and micro table saw or a Dremel tool in a pinch. As you said earlier, the correct plastic would have to be found as well as the proper bonding agent to attach the magnet to the plastic holder. As for the polarity issue, I can't see why one couldn't  place a compass next to a stock OEM magnet and see which pole is attracted to the magnet(s). Should it be, say, the South pointer that pointed to the magnet, then when you go to insert the New magnet in it's New Holder, Just make sure to orient the New magnet so that when held next to the compass the South pointer points the same way it did with the OEM mag. Once that is determind bond the magnet to the plastic insert. Of course, the plastic holder could be formed in such a way that there is a mechanical bond (snaps in place) between the two but an adhesive component couldn't hurt in that case either. Another method would be to form the plastic holder in such a fashion that the magnet is pushed into the holder from the front or the rear and a plastic "plug" inserted over the magnet. Of course the plug would be bonded to the plastic insert so that it would be as a one piece unit with the magnet "magically" sealed inside.

 

So many ways to skin that cat ain't there.

 

On the other hand, I was so impressed with the longevity of the Padgett method that I decided to use the JB Weld compound to coat and secure the brand new unmolested OEM magnet to the sprocket of and engine I'd reassembled not to long ago (2 years)

Photos included with this post.

 

John F.

Edited October 1, 2015 by Machiner 55 (see edit history)

[padgett]

Hope that is not any JB Weld on top of the interrupter, there is only .020" (+/-) clearance on the sensor.

[Machiner 55]

"Hope that is not any JB Weld on top of the interrupter, there is only .020" (+/-) clearance on the sensor."

 

It is JB weld on top.

First chance I get I'll pull the sensor and take a quick look-see and let you know what I see.

See?

 

John F.

[Ronnie]

John, I can't see the magnet locking arms on the front side of the sprocket in your photos. Did you break them off? If so why?

[ChrisWhewell]

Maybe one of the hole plugs down at the bottom of this link, then weld an appropriately-dimensioned magnet housing to the smooth surface.  Then, just push that sucker in the hole in the sprocket, but first put JB on the fingers.  Polarity important, yes.  Just take a second magnet to a store-bought replacement magnet, and adjudge which pole is facing outwards and copy that, no problem.  These hole plugs in the link aren't made for the job specifically, but with JB on the fingers, should stabilize it.  At least, its waayyy better than those two little plastic barbs on the replacement part you get at the auto parts store - that's the reason for the failure - the setback when the engine is stopped is just too much for those two puny plastic barbs to handle repeatedly.   Metal barbs - yes and JB to really hold that sucker.

 

https://www.surplussales.com/MetalPlugs/MetalHolePlugs.html

 

I wish I had a spare sprocket... want to loan me one ?      Its just been a busy week for business, clients are un-relenting.   Great discussion, 

Edited October 3, 2015 by Reattitude (see edit history)

[NTX5467]

An interesting "aftermarket-style enhanced fix".  I suspect the magnets are "longitudinally-oriented" rather than circularly-oriented, as was alluded to in an earlier post (speaking of rotating it in the holder, but putting it in from the wrong side of the sprocket didn't trigger anything).

 

On the assembly line, time is important, hence the snap-in situation, with the magnet already oriented, longitudinally, as it needs to be to do its switch-triggering function.  "Enhanced fixes", which take more time, can be done at replacement time.  The only question is just how long the life of the magnet will be?  If it works for 10 years, what about 20 years?  Just curious.

 

Ronnie, I remember the first Mallory LED triggered ignition conversion kits (mid-1970s), to replace contact points.  Pretty neat stuff, back then, and much more accurate than "points".  Back then, the Jessel timing belt kits were not available, whose additional timing accuracy came with the strong suggestion to check valve/piston clearances.  Of course, now everything's "electronic" ECM-controlled, which combined with OHC valvetrains and direct fuel injection make things happen humongously more accurately than in times past.

 

Thanks to Padgett for his contributions to more reliable motoring!

 

NTX5467

Edited October 3, 2015 by NTX5467 (see edit history)

[Ronnie]

I must be missing the point of all this. It seems like a quest to find a replacement for a part that is readily available and costs about the same as a Big Mac and fries.  Plus there is already an easy, reliable way of installing it.  I think the average failure rate for this part would measured in decades. When it does fail it hardly effects the way the engine runs so it isn't a part that would leave you stranded on the side of the road.

 

I admire your efforts to develop a new part for Reatta owners. It would be really helpful to have that brain power focused on finding/designing parts that are no longer available.

 

EDITED

Edited October 4, 2015 by Ronnie (see edit history)

[padgett]

BTW in my experience, the magnet does not fail, it is the plastic housing that holds the magnet.

Also once installed with JB Weld around the preiphery (and not the top) I just push in til the arms act as a stop. It is the JB Weld that holds and strenghtens the housing.

[ChrisWhewell]

Thanks !   But what of the old plastic magnet housing ?  Just push it through and let it fall into the oil pan  and forget about it ?   

[padgett]

Well the proper thing to do is to remove the engine, flush it out completely, and rebuild it. Few bother (if it soesn't get stuck in the sludge on the bottom of the pan, either the pump screen or the oil filter will trap the debris. Magnet will stick to whatever still steel piece it strikes first.).

[ChrisWhewell]

fudge it - I'm just gonna pull the cover and fish out the magnet housing and old magnet, install a new timing set and do JB on the magnet

[harry yarnell]

Nothing to do...?

[Machiner 55]

You may also want to consider dropping the oil pan to get what you're after.

 

John F.

[ChrisWhewell]

Yes, you're right of course.   arrgh.  Maybe just pull the whole thing and go with an L67   I'd never do it, but the thought crossed my mind to take the americium out of a smoke detector, glue it in the remnants of the plastic housing where the magnet used to be on the cam sprocket, then replae the cam pos. sensor with an alpha particle detector, lol.   I wrote 'cam pos. sensor' but am rethinking I should have written 'cam sensor pos'  

[padgett]

Well if I were pulling a cover think I'd replace the timing chain/sprockets/tensioner while there.

[ChrisWhewell]

yep.  Been putting a list together to do this on my '90.  So far, here's the list:

 

chain dampner 25535668

crank sensor and bracket

oil pan gasket

timing cover gasket set

2 heater hoses and bypass hoses

cloyes 3070 timing set

cam gear magnet

water pump

 

Trying to get it all before I rip it apart.   Whats this I hear about a pvc seal ?

 

Looks like a suspension part is in the way of removing the crank bolt & damper.   With so many manuals out there, its confusing as to which applies to my car so I'm just going to wing it !

[padgett]

Easiest way is with the car in the air to remove the wheel and inner fender liner. 90's have a brace that it is easier to remove. Also need to remove the woodruff key or you will tear the oil seal removing the cover.

[Barney Eaton]

If you are pulling the water pump.......get the little 90 degree hose that is a bypass.  easy to change when the pump is off....not easy when the pump is on.

[Guest xerxes66]

A question here - I just did Padgett's magnet replacement but wasn't aware of any "orientation" that might be needed on the magnet when I glued it in - is there an orientation element to this repair?

[Ronnie]

I think the answer is yes. Note in the photo below (from Padgett's  instructions) that the part of the magnet facing the sensor shows no signs of grinding. Installing it any other way I think would be a mistake.

 

Edited March 25, 2016 by Ronnie (see edit history)

[Guest xerxes66]

I  did it that way - I thought it meant a rotational orientation.

 

Terry

[padgett]

Rotation does not matter, polarity does. The little arms provide stops at the right depth and insure it goes in the right way.

[Guest xerxes66]

From what I hear, this is a common problem. If someone came up with an aftermarket "fix" that just plugs in from the front w/out J-B Weld it might be worth the investment. Anybody have an idea how many cars have this same configuration?

[padgett]

Probably around a million. 3.3, 3.8, 4.1, 3300, 3800

[Ronnie]

The silver rods you see on the four corners are the magnets.

 

 

 

[drtidmore]

Personally, the idea of ONE big magnet in a disintegrating plastic housing is way worse than 4 small magnets.  The 4 small magnets of the original design kept the metal fragments small as they fell into the timing gear area and eventually into the oil pan.  There is NOTHING inherently bad with 4 smaller magnets and I question if ANY plastic, that might have been or might currently be used, could retain its integrity longer than the original design.  Seems that most of us got a solid 20+ years out of the original design. 

 

As for whether there are multiple magnets in the original design, the answer is a resounding YES.  Many of us have, on replacement of the interrupter, found the interrupter with one or more magnets still housed in the failing plastic.  The most likely reason that the magnets were exposed rather than being totally encapsulated was purely a manufacturing compromise (i.e. injection mold the housing, snap the magnets in place afterwards).  

 

 

Edited July 5, 2016 by drtidmore (see edit history)