Almost Stranded at the Concorso

[mdivasc]

I was at the Concorso Friday and although my car has run flawlessly since the engine rebuild, and went down to Monterey (120 mi.) without incident, I couldn't restart it after it stalled, at idle, when I was leaving at the end of the day.

Luckily there were plently of Alfa guys around, and we figured out there was no spark to the plugs despite power coming from the coil to the distributor.
I was fortunate to have some very helpful folks around, and one very knowledgeable mechanic seemed to think the rotor in my distributor was incorrect for the updated bosch system I have.

I got a ride from the D'anna boat rep (sorry I don't remember your name, thanks) and went and bought a new rotor for a '71 VW bug, as was recommedded by the mechanic. It then started right up and worked well for the rest of the weekend.

Why would the previous rotor work for 6 months without issues and then just quit?

Here are some photos.

new VW rotor on the left and previous rotor on the right.

[tubut]

Why would rotors work and then quit?

Possibly because they were wrong to begin with -- i.e. a possible "substitute" that wasn't entirely correct because the "original part" wasn't available or too expensive or somebody made an honest mistake (remember, these are italian cars with many "undocumented features").

On that note, maybe the rotor was correct but the dizzy cap too big?

[alfazagato]

Its a veloce engine, with what appears to be a Marelli distributor and rotor arm but a Bosch cover with the cut-out...can that be? If so that may well be the problem!

[bshorey]

Quote:

Originally Posted by mdivasc I was at the Concorso Friday and although my car has run flawlessly since the engine rebuild, and went down to Monterey (120 mi.) without incident, I couldn't restart it after it stalled, at idle, when I was leaving at the end of the day. Luckily there were plently of Alfa guys around, and we figured out there was no spark to the plugs despite power coming from the coil to the distributor. I was fortunate to have some very helpful folks around, and one very knowledgeable mechanic seemed to think the rotor in my distributor was incorrect for the updated bosch system I have. I got a ride from the D'anna boat rep (sorry I don't remember your name, thanks) and went and bought a new rotor for a '71 VW bug, as was recommedded by the mechanic. It then started right up and worked well for the rest of the weekend. Why would the previous rotor work for 6 months without issues and then just quit? Here are some photos. new VW rotor on the left and previous rotor on the right.

[mdivasc]

Yes that was our theory as well the new rotor is a little bit bigger. What should that spacing be?

Also, the old rotor looks new there is no wear of significance.

[bshorey]

Quote:

Originally Posted by mdivasc Yes that was our theory as well the new rotor is a little bit bigger. What should that spacing be? Also, the old rotor looks new there is no wear of significance.

[Geezer]

Some rotors have a little resistor between the center & the tip. If the gap is too great that resistor can burn out.

I can't see the red rotor very well to tell if it has a resistor, but, I can see where the resistor should be on the black rotor. It's in the black area between the center contact & the tip.

BTW a plug gap that is too wide can cause the same rotor failure.

That's my story & I'm sticking to it.

[mdivasc]

no resistor on either rotor that I can see.

[Geezer]

Quote:

Originally Posted by mdivasc no resistor on either rotor that I can see.

[mdivasc]

I had already checked that, on the old rotor, 0 ohms.

Haven't checked the new one.

[velocedoc]

Mike, I am glad that you found the issue. I was thinking it was the fuses, but I knew you said you checked that. This one almost stranded you. At least it wasn't on the highway! Usually you buy a cap and rotor that match, so the spacing is correct. It probably isn't more than the width of a spark plug gap or less, would be my guess for the gap. I was going to suggest you ground the distributor wire from the coil to see if it makes spark, but your friend was on the phone. Truly one odd problem, and glad you got home ok.

[mdivasc]

Thanks to all the help from the car guys at the Concorso, I couldn't have made it home without you. And now the car runs well also.

[alfazagato]

Pleased to know all is well, but to answer my query.... what make is the distributor? If a VW arm works it suggests a Bosch unit, Veloces usually have Marelli, the red rotor arm is a Marelli pattern yet the cover has the Bosch cut-out. If it is a Bosch unit and had the wrong rotor arm then it is clear what has happened!

[mdivasc]

Turns out that the marelli rotor (red) in the photo had an internal fault and would not conduct to the arm.

Yes it was the wrong rotor for the bosch distributor, but it still worked until it failed internally.

After removal of the metal bit on the inside, there was evidence of a carbon mark/crack which allowed to ground out rather than conducting to the rotor arm.

[alfazagato]

Thought so!