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Posted by: Gatornapper Dec 6 2021, 06:49 PM

Fellow 914'ers -

Two years ago Brandt sold me a great and rare 050 dizzy that instantly made my old 2.0 run better than ever.

I've run it hard for 4,000 miles with no problem. I have run an MSD in the car since it had one when I got it, but I did replace it with a new one a few months ago.

The old cap showed wear so I put in the new cap when I installed the 050, but the rotor looked good so I used it.

Engine died suddenly and wouldn't start last Saturday (27th) and I found this:



Resistor in the rotor blown to smithereens. After 2 years and 4k miles.

Thankfully is was an old rotor that came in the dizzy, but Brandt also included a new cap and rotor - both hard to find. So the new rotor will go in tomorrow. Cap looks fine.

My question is: what blew this rotor? Was it the MSD? Is the MSD voltage too high for this rotor? Or was it just old and had lived out its life?

Due to the uniqueness of the 050, I'm pretty certain a rotor w/o the resistor cannot be found.

Thoughts from the braintrust are greatly appreciated.

Thinking of soldering in a wire where resistor was tho I'm not sure it can take the heat. Also will carry a spare rotor with me in the car.

GN

Posted by: 914_teener Dec 6 2021, 07:00 PM

This: "just old and had lived out its life.."

2nd law of thermodynamics by the looks of the cracks in the rotor.

I'd get a 123 Dizzy but I don't think you can run the MSD coil with that dizzy...could be wrong but don't think you can.

I pull the mechnical dizzy that you have source parts if any and keep it as a spare in the car.

My 02.

Posted by: Retroracer Dec 6 2021, 07:17 PM

Over a standard 12V spark gap and coil system, the MSD will present a much higher voltage to the primary side of the coil, as well as multiple spark events (CDI) for each firing - stressing that resistor MUCH more than it was probably designed for.

Interesting, I've never see a resistor integrated into the rotor before. If it was me, I'd solder a link over to see if it still functioned (the MSD will be fine and the spark plugs won't care. A wire link won't get hot as there's very little resistance to dissipate any power!), but as pointed out earlier, those cracks in the rotor insulation are an indication that it is not long for this earth...

FWIW,

- Tony

Posted by: Gatornapper Dec 6 2021, 07:27 PM

Thanks guys. I think the resistor overheated and caused the thermal damage, eventually being burnt up itself. Lots of old rotors have resistors in them, but they are hidden.

Cracks are only on surface, not deep, so a soldered wire may be ok.

I ordered new cap & rotor at Zims - very expensive - but soon will have spares.

A 123 is on my wish list. For sure. Funds now flowing into the 924 Turbo resto.

Gotta make a plug for 914world.com here.

This is the best group on the web, by far. I'm on a lot of forums for cars, bikes, tractors, etc. This board has spoiled me. Every question - answers in a very short time.

924 board is sad. Days, weeks - no responses or replies. I know the 931 (internal name for 924 Turbo) is a rare car, but it has its own sections. But few people on them. Only 2 or 3 guys have replied to my questions. Sad.

But then, I'm spoiled here.

You all here are THE BEST!

GN

Posted by: 914Sixer Dec 6 2021, 07:46 PM

Yep, the 931 are rare critters. I had the 81 Turbo for about 2 yrs. Badass when the turbo spooled up., 100 mph comes up VERY quick.

Posted by: Gatornapper Dec 6 2021, 09:05 PM

And that with only 150hp? Discontinued as the 2.5 engine NA engine produced that.

Actually the '80 931's are only 143hp. EU ones were 170. I think the '81/'82's were 150hp.

Can't wait to find out. Hope to have engine running this week.......be a nice Christmas present........

GN

QUOTE(914Sixer @ Dec 6 2021, 08:46 PM)

Posted by: Gatornapper Dec 6 2021, 09:13 PM

Some information on resistor rotors....resistors initially put in to reduce static for AM radios.....

https://xwebforums.com/forum/index.php?threads/quick-resistor-rotor-to-non-resistor-rotor-conversion.37616/

Posted by: Krieger Dec 6 2021, 09:15 PM

The MSD should be run with a rotor that has no resistor. Used to be able to buy rotors without them. Here is a link from Pelican that discusses the issue:

http://forums.pelicanparts.com/porsche-911-technical-forum/544061-ignition-rotor-meltdown.html

Posted by: Krieger Dec 6 2021, 09:25 PM

I modified both of the rotors on my cars. 914 2.0 4 cyl (rev limited rotor) and 911 3.0 per this Pelican article. I didn't remove the resistor, but ground out enough of the epoxy to lay in 1/8" brass rod to solder in above it.

http://forums.pelicanparts.com/porsche-911-technical-forum/596559-msd-rotor-modification-detail.html

Posted by: Mark Henry Dec 8 2021, 08:37 AM

I have a several of those rotors, but 2 are aftermarket and they have solid copper contacts, no resistor. These two the skirts are much shorter than the OE but I think they still fit.

I've heard of guys digging the resistor out and soldering in a heavy (12ga?) chunk of copper wire in its place.

Posted by: maf914 Dec 8 2021, 02:51 PM

Here is an Ebay listing for 050 rotors. Don't know anything about the quality.

https://www.ebay.com/itm/115020463565

And here is a listing for 050 caps. Again don't know anything about the quality.

https://www.heritagepartscentre.com/us/ac905051-distributor-cap-for-bosch-050-distributor.html?cid=15207429358&aid=124696668850&kw=& amp;gclid=Cj0KCQiAzMGNBhCyARIsANpUkzOZiPme8i5yT6fBm1HPNxqSZni_2XzERvbECmorXTSc33
rgtRAkLMAaAv-8EALw_wcB

Posted by: Gatornapper Dec 9 2021, 10:03 AM

Thanks - but looks like these rotors have the resistor.

Yeah - I'm gonna solder in a piece of #14 ga. copper where the resistor was in the old one and run it.

GN

QUOTE(maf914 @ Dec 8 2021, 03:51 PM)

Posted by: Gatornapper Dec 9 2021, 10:07 AM

Krieger, Mark, Andy -

Thank you.

GN

Posted by: Gatornapper Dec 9 2021, 10:27 AM

SUPER BUMMER!

See here:

http://www.914world.com/bbs2/index.php?s=&showtopic=159774&view=findpost&p=2965733

Maybe continue replies here rather than on "What did you do..." thread.....

GN

Posted by: johnhora Dec 9 2021, 12:32 PM

GN...
have you checked over on the thesamba.com
lots of bus guys there with type 4 engine

Posted by: JamesM Dec 9 2021, 10:31 PM

QUOTE(Gatornapper @ Dec 6 2021, 08:05 PM)

And that with only 150hp? Discontinued as the 2.5 engine NA engine produced that.

Actually the '80 931's are only 143hp. EU ones were 170. I think the '81/'82's were 150hp.

Can't wait to find out. Hope to have engine running this week.......be a nice Christmas present........

GN

QUOTE(914Sixer @ Dec 6 2021, 08:46 PM)

Yep, the 931 are rare critters. I had the 81 Turbo for about 2 yrs. Badass when the turbo spooled up., 100 mph comes up VERY quick.

Posted by: michael7810 Dec 10 2021, 06:23 AM

Had the same thing happen on a Rt 66 event and Brant came to the rescue with a new rotor. I then installed one without the resistor from aircooled.net and it was still OK 10K+ miles later when I sold the car. I also had MSD ignition.