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MG TD TF 1500 - Using Pertronix, check your rotor.

After a bunch of measurements and a lot of images I think I now know why my ignition failed recently. It looks as if the magnet collar of the pertronix Igniter uses up all of the vertical free space in the distributor. The spring loaded brush is pushed fully into the recess in the cap. This causes the top surface of the rotor to press against the inside of the cap. This will leave a circular rub mark on the rotor. It may not be as bad as is shown in the attached image, but it shouldn't be that way. Catastrophe will follow.
Some rotors are more susceptible than others. The magnitude of this is only about .020". Bud


Bud Krueger (TD10855)

Have a look at http://www.ttalk.info/Failure.htm Bud
Bud Krueger (TD10855)

Bud,
I had a rotor do much the same about three years ago (in the MGB)...I noticed that with the mag collar on the rotor seemed to sit to high...I now take a bit off the rotors with sandpaper...low tech fix but it seems to work.
Bob Dougherty

Bud,
Your commitment to these cars is truley to be commended!
WOW ..a cut-away view!

Wish I just had a nickle for every time I have directed someone to your site.
(The guy down the road I ran into a few months ago at store in a TD stopped by the other day to thank me for directing him to your site.)

Thank you so much for all your support over the years.
Cheers,
David
David Sheward

now that i'm reading this...it seems familiar. i can't remember if it is in the archives or not..butsomewhere i read about interference with the cap/rotor with the pertronix collar. hmmm...now i'll have to look. glad you figured this one out bud. regards, tom
tom peterson

there it is. from may to june of '08. i THOUGHT this seemed familiar! regards, tom
tom peterson

That rotor was one that I showed in the '08 thread. At the time I didn't realize how destructive the interference was. Bud
Bud Krueger (TD10855)

When I installed the Pertronix system in my distributor, I could not clamp the distr. cap into place. There was a lot of discussion on this BB about the problem and it turned out that I had to remove some material from the bottom of the rotor so it could sit lower within the cap. It was a simple solution but I always felt that a change should be made by the manufacturer and not the customer. It appears that nothing has changed because the subject keeps coming back. I think the product is good but it should not be up to the user to make the correction. This is Utopia isn't it?

George
George Raham [TD4224]

George, I think the problem is that the magnet collar has to have a lip on the top to keep it from pushing downward off of the cam. The lip is what keeps the rotor from fully seating. It would be nice if they put something in the directions about this interference however. The Pertronix is a huge improvement over the old Crane electronic, with its separate box, and Micky Mouse screwed together brackets to hold the pick-up. George
George Butz

Hi Bud Just a thought But have you checked the height of the drive shaft, I have some experience on other peoples cars using rebuilt 25 and 45D distributors the height of the shaft is too high i.e., incorrect shim thickness under the drive shaft lifting the shaft too high which is causing the same problems as you are experiencing and also premature failure of the module. Hope this will help.
Regards
Keith
p.s. Recently met a young lady from Massachusetts who has married and settled in my home town and loves the weather!
k harris

George Butz The Crane system is an OK working system but it does have that extra box. When I used one I fastened it to the support for the firewall. Now I use the Pertronix and don't see any improvement over the Crane.

Just my $0.02 worth.
Bob
Bob Jeffers

Bob, I ran the Crane for years- yes it worked great, I was just refering to the ease of installation, extra wires, and the cheesy pick-up mounting brackets. I agree with you- no difference from Pertronics as far as running- both vastly better than points. George
George Butz

Great cross sections, Bud. Thanks.
I have pertronix and a red rotor in my TF. I have a Lucas cap. All seems to be OK, but I'm thinking I should shave a few thou off the rotor. To cut to the chase, how do I do it?
Coarse sandpaper and 10 minutes of back and forth on the rotor base, or something else???

Tom
Tom Norby

Tom, I 'cheated' and touched the rotor to the flat side of a grinding wheel for the first cut. Then I ran across sandpaper until I got to .030" off. The metal spring inside the rotor is a bit resistant to sanding.
I'm going to section a rotor and see if I can't get more quantitative data on the needed dimensions. Bud
Bud Krueger (TD10855)

George I agree on the cheesy brackets! I forgot to mention that I never used the original brackets. I machined a block and silver soldered it to a new plate I made to replace the points plate. That was a solid way of holding the pickup.
Cheers,
Bob
Bob Jeffers

A few more images showing the rotor on the distributor cam with and without the magnetic sleeve.
http://www.ttalk.info/Failure.htm Bud
Bud Krueger (TD10855)

Guess I have to ask why this is not an issue on my car. Early TD. Put a pertronix in about 5 years ago and have not had this problem. I am not running the red cap and that may be why.
Bruce Cunha

Bruce,

In my thread noted above, the rotor I had to modify was black, so I don't think the colour is any indication of a rotor that has to be shortened.

George
George Raham [TD4224]

Interesting Pertronix comments on the same issue at

http://www.british-cars.net/mgtd-mgtf1500-bbs/pertronix-problem-2008040519425512180.htm

Mike
Mike Hart (52 TD 16378)

That thread is from some discussions we had about two years ago. The 'rocking cap' syndrome wasn't looked at in terms of what's going on if the cap's not rocking, but it's too tight. As seen, the center contact of the cap can be physically pressing against the top of the rotor, causing damage. The spring-loaded carbon brush becomes useless. Not all rotors have the same interior, or height, dimensions. I've found that the use of one of the red rotors from Advanced Distributors, with .030" removed from its height, puts the carbon brush back in operation. Bud
Bud Krueger (TD10855)

Maybe somebody ought to figure out the correct relative positions of the cam, rotor, & cap relative to the distributor body top face. And since all this stuff could vary, a common reference might be more useful than "chop about this much off this colour part" etc.

It would not be unlikely that many distributors are way off from where they were originally, given wear and the usual attitude toward actually measuring and correcting critical dimensions. This is probably the main cause of these problems, given that some people have no problems fitting the Pertronix without mods or trouble. I suspect Pertronix did a certain amount of homework, since they "usually" fit.

Many other "mysteries" might be solved by sorting the distributor shaft position and play before using a bunch of SortaFix.

I don't have a T myself or easily accessible to start this process off. My suggestion would be to inquire of somebody like Jeff Schlemmer, and any known NOS distributors that might be squirreled away, and then add actual verified measurements as people find them. Put all this in a database, maybe on Bud's fine site. Then it should not be difficult to make up a Go/No gauge template that could be printed out, all referenced from the locating face of the distributor body/cap.

Just read the link Mike gave, pretty well covers it all. It seems to me that in order to protect themselves Pertronix ought to provide the gauge, or at least an explanation that the installer needs to check this. Other than that, it is up to people playing with complex objects to pay attention, and I know it is difficult, given all the "wrong" stuff supplied and used.

FRM
FR Millmore

FRM -- for the first time ever, I'm not getting a response from my contact at Pertronix. I'm in communication with Jeff Schlemmer about this issue. I'm about to head to the basement to start work on a test gauge based on a comment from Jeff. Stay tuned. Bud
Bud Krueger (TD10855)

This thread was discussed between 08/09/2010 and 16/09/2010

MG TD TF 1500 index

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