Blown Rotor on 050 Bosch dizzy, Resistor blown on rotor - why? |
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Blown Rotor on 050 Bosch dizzy, Resistor blown on rotor - why? |
Gatornapper |
Dec 6 2021, 06:49 PM
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#1
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
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: (IMG:http://www.914world.com/bbs2/uploads_offsite/hosting.photobucket.com-21449-1638838169.1.JPG) 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 |
914_teener |
Dec 6 2021, 07:00 PM
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#2
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914 Guru Group: Members Posts: 5,245 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
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. |
Retroracer |
Dec 6 2021, 07:17 PM
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#3
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Senior Member Group: Members Posts: 620 Joined: 7-July 13 From: Bend OR Member No.: 16,100 Region Association: Pacific Northwest |
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 |
Gatornapper |
Dec 6 2021, 07:27 PM
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#4
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
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! (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/smilie_pokal.gif) GN |
914Sixer |
Dec 6 2021, 07:46 PM
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#5
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914 Guru Group: Members Posts: 8,989 Joined: 17-January 05 From: San Angelo Texas Member No.: 3,457 Region Association: Southwest Region |
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.
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Gatornapper |
Dec 6 2021, 09:05 PM
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#6
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
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 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. |
Gatornapper |
Dec 6 2021, 09:13 PM
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#7
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
Some information on resistor rotors....resistors initially put in to reduce static for AM radios.....
https://xwebforums.com/forum/index.php?thre...nversion.37616/ |
Krieger |
Dec 6 2021, 09:15 PM
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#8
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Advanced Member Group: Members Posts: 4,754 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None |
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...r-meltdown.html |
Krieger |
Dec 6 2021, 09:25 PM
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#9
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Advanced Member Group: Members Posts: 4,754 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None |
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...ion-detail.html |
Mark Henry |
Dec 8 2021, 08:37 AM
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#10
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
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. |
maf914 |
Dec 8 2021, 02:51 PM
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#11
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None |
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/ac90...MAaAv-8EALw_wcB |
Gatornapper |
Dec 9 2021, 10:03 AM
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#12
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
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 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/ac90...MAaAv-8EALw_wcB |
Gatornapper |
Dec 9 2021, 10:07 AM
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#13
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
Krieger, Mark, Andy -
Thank you. GN |
Gatornapper |
Dec 9 2021, 10:27 AM
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#14
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Senior Member Group: Members Posts: 1,259 Joined: 22-September 17 From: Woods west of Richmond, VA Member No.: 21,449 Region Association: South East States |
SUPER BUMMER!
See here: http://www.914world.com/bbs2/index.php?s=&...t&p=2965733 Maybe continue replies here rather than on "What did you do..." thread..... GN |
johnhora |
Dec 9 2021, 12:32 PM
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#15
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Senior Member Group: Members Posts: 873 Joined: 7-January 03 From: Derby City KY Member No.: 107 Region Association: None |
GN...
have you checked over on the thesamba.com lots of bus guys there with type 4 engine |
JamesM |
Dec 9 2021, 10:31 PM
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#16
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Senior Member Group: Members Posts: 1,965 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
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 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. My 80 had a manual boost controller installed when i picked it up. Its amazing how much power a little more boost adds. Amazingly fun cars, It feels like a mix of my 951 and my 914, which is pretty much exactly what it is. |
michael7810 |
Dec 10 2021, 06:23 AM
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#17
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Senior Member Group: Members Posts: 1,082 Joined: 6-June 11 From: Scottsdale, AZ Member No.: 13,164 Region Association: Southwest Region |
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.
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