foster461 Posted October 5, 2015 Report Share Posted October 5, 2015 On our club tour today everything was going well until we heard a loud "pop" from the engine area followed by the engine shutting down. We were on a bend in a narrow road but had enough people to manage traffic while we investigated. It didnt take long to find the culprit. This rotor probably has done less than 1000 miles. I dont know if this was due to a component failure or something systemic. The distributor itself seems fine, no wobble in the shaft. No obvious issues with the cap. I always carry a spare cap and rotor so it was a five minute fix but any ideas what happened ? Stan Quote Link to post Share on other sites
ctc77965o Posted October 5, 2015 Report Share Posted October 5, 2015 Looks like a dielectric failure...sparking thru the plastic to earth...but what earth is below the rotor? is there any metal part directly below ? normally the poorly made ones short to the shaft..as thats the only earth around.. Quote Link to post Share on other sites
foster461 Posted October 5, 2015 Author Report Share Posted October 5, 2015 This is a Bosch rotor and is all plastic other than the metal rotor strip running across the top. There is a small spring steel strip to keep it tight to the shaft. It apparently got very hot and vaporized some of the plastic. Quote Link to post Share on other sites
Don H. Posted October 5, 2015 Report Share Posted October 5, 2015 Very hot indeed, Stan. Those thermoset plastics take a fair amount of heat. They'll never melt -- but they'll char, as you saw. I'm guessing, but it might have been a manufacturing defect in the molding or the conductor that resulted in arcing, erosion, and your eventual stop. I'd guess that damage didn't happen in one swell foop. Quote Link to post Share on other sites
ctc77965o Posted October 5, 2015 Report Share Posted October 5, 2015 You say it was running well before the "pop"?? It looks like the type of failure that would cause a misfire... Quote Link to post Share on other sites
foster461 Posted October 5, 2015 Author Report Share Posted October 5, 2015 You say it was running well before the "pop"?? It looks like the type of failure that would cause a misfire... Yes Dave, before the Pop it was running ok. I did notice that after I did the cap and rotor swap it started easier and was a bit happier but something in the instant that it went Pop was the final nail in the coffin. I think Don is right that this has been going on for some time but with no points to check I had no reason to open up the dizzy. Clearly a false assumption on my part. Stan Quote Link to post Share on other sites
stuart Posted October 5, 2015 Report Share Posted October 5, 2015 Do you know if the rotor was a genuine Bosch or not? Stuart. Quote Link to post Share on other sites
foster461 Posted October 5, 2015 Author Report Share Posted October 5, 2015 Do you know if the rotor was a genuine Bosch or not? Stuart. The 123 is sold as "get caps and rotors from your local auto parts store" so mine came from NAPA. What I'm reading though is not all rotor arms are born the same and the aftermarket rotor arms dont always fit properly on the 123 shaft. If you google "123 rotor melted" you can find other examples. Not good. Stan Quote Link to post Share on other sites
stuart Posted October 5, 2015 Report Share Posted October 5, 2015 IIRC The Bosch one is listed as being from a Volkswagen, Guy (Jersey Royal) usually keeps cap and rotor as a spare in his trunk. Stuart. Quote Link to post Share on other sites
foster461 Posted October 5, 2015 Author Report Share Posted October 5, 2015 IIRC The Bosch one is listed as being from a Volkswagen, Guy (Jersey Royal) usually keeps cap and rotor as a spare in his trunk. Stuart. That would be useful info Stuart, I'll send Guy a note and ask him. The 123 docs for this distributor lists 4 different Bosch part numbers for the cap and one part number for the rotor but they dont mention what vehicles they were originally fitted to. I'm guessing VW, Merc and BMW to start with but the VW dealer may be cheaper and they suddenly need the business. Stan Quote Link to post Share on other sites
john.r.davies Posted October 5, 2015 Report Share Posted October 5, 2015 (edited) If you'll look closely isn't the metal tip pushed into the body? It should project slightly. It must have hit a terminal in the cap, buckling the thin strip between it and the central contact, the buckle then went high resistance and over heated. Cause: worn bearings on dizzie shaft. Check closely for a damaged terminal, and when you have replaced it, get it checked for dwell variation. John Edited October 5, 2015 by john.r.davies Quote Link to post Share on other sites
Icarus60 Posted October 5, 2015 Report Share Posted October 5, 2015 I have used a 123 tune on my 3A since they became available. My cap and rotor came from here http://www.accuspark.co.uk/rotors.html No problems for far and just looked at the rotor and no sign of arcing or contact. I keep the Lucas original set up in the boot but haven't needed it yet. Hope you get sorted OK Regards Rog Quote Link to post Share on other sites
jean Posted October 6, 2015 Report Share Posted October 6, 2015 Nothing is perfect, On my 6 I had a catastrophic failure with the famous red rotor, which I bought at Malvern IWE years ago. One day when I fired up the engine it suddenly broke to pieces. And it was a so said ORIGINAL.... So even the best of the best can fail... Quote Link to post Share on other sites
RogerH Posted October 6, 2015 Report Share Posted October 6, 2015 Hi Jean, there are 'Red' one, there are 'original' one and there are 'Dizzy Doc' ones. Everybody appears to be doing and has done red ones. The originals became none original quite a long time ago. That is why Martin got them remade properly only in recent memory. Roger Quote Link to post Share on other sites
EdwinTiben Posted October 6, 2015 Report Share Posted October 6, 2015 Do you have a good earthing to the engine ? Have seen problems with electrics, 123 and bad earthing.. Quote Link to post Share on other sites
roy53 Posted October 6, 2015 Report Share Posted October 6, 2015 Nothing is perfect, On my 6 I had a catastrophic failure with the famous red rotor, which I bought at Malvern IWE years ago. One day when I fired up the engine it suddenly broke to pieces. And it was a so said ORIGINAL.... So even the best of the best can fail... But was it from Distributor Doc ? Quote Link to post Share on other sites
foster461 Posted October 9, 2015 Author Report Share Posted October 9, 2015 I did some exploration into the failed rotor arm. It seems that the center termional is connected to the tip via some sort of fibrous material that my meter is declaring as non conductive. I assume that this rotor arm has/had a built in resistor and it was that resistor that failed. Quote Link to post Share on other sites
Don H. Posted October 9, 2015 Report Share Posted October 9, 2015 Do you know Jeff Schlemmer at Advanced Distributors, Stan? He'd be my next port of call... http://advanceddistributors.mybisi.com/product/4-cylinder-ignition-rotor Quote Link to post Share on other sites
foster461 Posted October 9, 2015 Author Report Share Posted October 9, 2015 Do you know Jeff Schlemmer at Advanced Distributors, Stan? He'd be my next port of call... http://advanceddistributors.mybisi.com/product/4-cylinder-ignition-rotor Jeff is a good guy Don and he has rebuild several Lucas units for me. This failure was in a 123 Ignition distributor though, different animal that uses Bosch compatible parts as fitted to beamers and porkers in the mid 70's. Stan Quote Link to post Share on other sites
jean Posted October 9, 2015 Report Share Posted October 9, 2015 Correct Roy...it was the first time Martin did sell them at the IWE, but I can't blame him for that......even a million$ RR jet engine can fail.. Quote Link to post Share on other sites
Don H. Posted October 9, 2015 Report Share Posted October 9, 2015 Jeff is a good guy Don and he has rebuild several Lucas units for me. This failure was in a 123 Ignition distributor though, different animal that uses Bosch compatible parts as fitted to beamers and porkers in the mid 70's. Stan Yeah, I thought Jeff might have some insight into what blew up in your rotor, and what bits might be a better choice. He'd be on my "consult" list. If you need a 70s era German four cylinder rotor -- I might have an NOS Audi Fox one around here someplace! Quote Link to post Share on other sites
foster461 Posted October 9, 2015 Author Report Share Posted October 9, 2015 Here's a similar discussion in another forum where they are blaming the integrated resistor for the meltdown and how they are bypassing the resistor. http://forums.pelicanparts.com/porsche-911-technical-forum/493184-anyone-ever-see-distributor-rotor-do.html Quote Link to post Share on other sites
john.r.davies Posted October 9, 2015 Report Share Posted October 9, 2015 A Resistor? In the Rotor arm? Shurely shome mishtake? That was presumably a suppression device, instead of extra resistors in the HT cables or connectors, but ill-advised in view of the adverse conditions at the rotor arm. I still think the tip contacted a terminal - that would have precipitated this event and the sudden cut-out. John Quote Link to post Share on other sites
foster461 Posted October 10, 2015 Author Report Share Posted October 10, 2015 A Resistor? In the Rotor arm? Shurely shome mishtake? That was presumably a suppression device, instead of extra resistors in the HT cables or connectors, but ill-advised in view of the adverse conditions at the rotor arm. I still think the tip contacted a terminal - that would have precipitated this event and the sudden cut-out. John Yes 007, that is what I understand. More info here: http://www.ba7c.org/technicalArticles/rotorArmsBosch.html There was no sign of the rotor hitting anything. It was just arcing internally in multiple places and suffered a meltdown with the tip eventually getting detached from the resistor. Stan Quote Link to post Share on other sites
mikeKuk Posted September 16, 2020 Report Share Posted September 16, 2020 I have exactly the same issue - two rotor arms melted in under 500 miles of driving my Spit6 with 1-2-3 distributor fitted...anyone found a fix yet ? Quote Link to post Share on other sites
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