Pertronix Failure Question - PeachParts Mercedes-Benz Forum

350SL4spd · #1 03-13-2008, 04:24 PM

Hey all,

I installed an Ignitor 1885 and Flamethrower coil on my '72 350SL M116 while trying to fix a horrible surging/runability problem (new plugs/wires/cap/rotor/etc/etc were installed first & D-jet system was checked up & down). It ran better for a while and then started missing on couple of cylinders. The miss was confirmed by finding wet plugs on #'s 3 & 7 (next to each other in the firing order).

I pulled the Cap off and found what appeared to be a separation in the Pertronix magnet (pictured below). Am I right in thinking that a separation like that would cause a miss?

I remember when I installed it I thought it was too tight. Hell, it's entirely possible that it was too small of a magnet for my dizzy and it cracked when I put it on. I honestly didn't inspect it closely after installation...

How would I go about ordering an slightly larger diameter magnet from Pertronix? Anyone have one in a M116 that we could compare?

Arthur Dalton · #2 03-13-2008, 04:50 PM

http://www.vintageperformance.com/retrorockets/field_test.htm

350SL4spd · #3 03-13-2008, 04:55 PM

Thanks for the link Arthur.

I'm not sure that the miss would be noticeable in that test. I know the transistor hasn't failed because the car runs. I'm just not sure if the gap in the magnet would cause a miss...

Mike D · #4 03-13-2008, 05:17 PM

Yup, it would cause a miss! The separated magnets will be "firing" out of time due to their misalignment regarding the "flats" of the distributor shaft.

Figure the 1st cylinder in the order triggers at 0, 2nd at 60, 3rd at 120, 4th (before the gap) at 165, 5th at 220, 6th at 300 (in degrees) and of course the gap would expand as rpms increase.

350SL4spd · #5 03-13-2008, 05:24 PM

That was basically my logic...

Can anyone w/ an M116 tell me which magnet they're using? (Are they even numbered??) I don't want to order another one and have the same thing happen because it actually is too small for my dizzy...

Tony H · #6 03-13-2008, 05:48 PM

I have a Pertronix on my car. I can look at it tonight.
Tony

Arthur Dalton · #7 03-13-2008, 06:17 PM

Are you using the Pert 1 or 2 ..and did you eliminate the Benz Transistor switchgear??

350SL4spd · #8 03-13-2008, 06:27 PM

Thanks all.

Tony, that would be great.

Arthur, I'm running a Pertronix I #1885.

Arthur Dalton · #9 03-13-2008, 06:29 PM

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See if this helps ..try and match your dist ID #.

http://www.vintageperformance.com/retrorockets/mercedes.htm

I think you may just have forced it down a little cocked and cracked it..it takes a nice even pressure and perfectly aligned to install proberly.

Have you disconnected the Benz switchgear??

Arthur Dalton · #10 03-13-2008, 06:36 PM

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........... 8 cyl engine

350SL4spd · #11 03-13-2008, 07:02 PM

Arthur,

Yeah, switch gear is disconnected. Wiring is as follows:

Arthur Dalton · #12 03-13-2008, 07:31 PM

Yeah..that's cool.... I like that you ran that extra ground from the dist..common source of problems with old distributors.
I only ask about the switchgear b/c many still leave it in the circuit with the Pert, not realizing they are then switching the Pert with the SG..no good.
I also asked about the Pert 2 b/c that requires you use resistor wires instead of solid core ..not recommended.

I think you are just out of time b/c of the split throwing the fire timing angle off , as Mike D post was getting at.
O-scope would verify that, but I would not even bother ..just get a new one and be careful w/install..
I have seen where they did have a problem with one of their pick-ups and came out with a replacement with a white dot on it so as to ID the modified version..you may want to give them a ring before replacement..

This has also been discussed in the Archieves.

Tony H · #13 03-13-2008, 07:32 PM

Still not home (2+ hrs of road time in front of me)
Have you checked your trigger points? Dirty trigger points will cause all sorts of drivability issues. The fuel injectors fire in 4 groups of 2 injectors so if 2 consecutive cyl. in the firing order are missing that could be the(or part of) problem. My trigger points were dirty when I bought my car and it would hardly run. The PO had thrown $$$ of new parts at the problem and finally gave up.

350SL4spd · #14 03-13-2008, 09:57 PM

Trigger points are clean. That's one of the first things that I did.

nhdoc · #15 03-14-2008, 09:31 AM

I had to replace the magent on my pertronix too. I think that I didn't have it positioned perfectly on the cam lobes and after that it would not go on the spindle correctly. You might even be able to repair it but replacements are available.

I ordered a replacement from Retro Rockets and they stocked it, so it is probably a common problem. Good luck.