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MG TD TF 1500 - Pertronix Ignition

I've had a pertronix ignition in my distributor for the last 5 years. Yesterday I removed the magnetic portion that goes over the distributor cam and it came apart - apparently the glue had deteriorated and the 4 little magnets ended up stuck to the distributor cam.

I've replaced them in the holder but not sure I'm orienting them correctly. Depending on their placement (N/S magnetic field) I can get the car to run on 3 cylinders, 2 cylinders or 1 cylinder - but not 4. I've tried a new cap, wires and rotor so I know it's the magnetic portion that's messed up.

So, barring someone on here that knows how to replace the magnets correctly, I need to order a new unit. I don't remember whether I originally ordered one to fit an asymmetric cam profile or a symmetric/high lift cam profile and I'm sitting here at work 50 miles away from the car so I'd like to get a sampling of people that have a Pertronix unit in their cars. Which profile did you order?

Thanks in advance.

Gene Gillam

Gene, I have an LU-146 system in mine (symmetric/high lift). It's a late '53 engine. BTW, the magnetic collar is an LU-142A. See http://www.ttalk.info/Tech/Pertronix_Into_TD.html. Any chance you could get a picture of the magnets?
Bud Krueger

Bud,

I visited your site several times last night/today trying to identify which unit you were using. I called Petronix technical using the 1-800 number you provided and found out that all the magnets have to be 'south facing'. I think the last way I left 'em last night had to be all 'north facing' since it wasn't firing at all - hopefully I can mark 'em, then rotate 'em and get 'em in right this evening sometime.

As far as getting a photo of them I'm sure I can but it wouldn't show very much - they're little oblong magnets about 1/4" long by 1/8" wide, one set at each lobe of the distributor cam.

Gene

Gene Gillam

Gene, see http://www.ttalk.info/Tech/BoxAndAll.jpg and
http://www.ttalk.info/Tech/LU142A.jpg Good luck. Bud
Bud Krueger

Gene -- The "south facing" means that the hall cell in the Pertronix unit is turned ON by the south pole and OFF by lack of a magnetic field. This mode of operation is often called biased, another mode is called bipolar which is when a north pole is required to turn the hall cell Off.

You can orient your magnets by use of a Boy Scout type compass. Set the magnets fairly far apart (8-10 inches). Then bring the compass toward the magnets from the direction of the hall cell (i.e. end-on or broadside). The end of the needle that points North will point to the south pole of the magnets (opposites attract). When all thats done it should fire on all four cylinders.

If perchance it does not, determine which cylinder is not firing. Then remove and rotate the magnet assembly one cylinder. If the same cylinder is not firing then the problem is not with the Pertronix, but with some other thing (spark plug, dist. cap etc.). If the cylinder not firing moves with the change in the position of the magnet assembly, one of the magnets is not right.

I've worked with Hall Cells for more than twenty years and they are fun devices and very useful. Funny the Hall effect was discovered back in the 19th century but until integrated circuits came along it wasn't of much use. Too small an output.

Hope this helps,
Bob
R. K. (Bob) Jeffers

Bob,

That explanation helps a heck of a lot. I was trying to use a compass last night but I was pointing the magnet at the compass instead of holding it broadside to it - and that didn't work. I'll try this method when I get home - but I've also found enough pieces and parts to put together a 'points' system if I can't get this to work.

Appreciate your taking the time to explain things better.

Gene

Gene Gillam

Bob,

Just to let you know...

Got home tonight, followed your advice and had the car running within 10 minutes.

It was the 'broadside' hint that did the trick. Now all I need is some superglue to keep it from falling apart again and I'll be set.

Again...thanks,

Gene
Gene Gillam

Gene -- I would suggest epoxy over superglue, IMHO superglue is quick and all that but not too permanent. Epoxy on the other hand is very permanent. Even the five minute type is better IMHO than superglue.
Good Luck and thanks for the feedback,
Bob
R. K. (Bob) Jeffers

This thread was discussed between 05/09/2006 and 07/09/2006

MG TD TF 1500 index

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