"...conducted the heat through it..??

Just doesn't seem likely......

 

"We are speaking here of maybe a dozen instances going back to the early 70's but I don't remember ever replacing a regulator internal to the alternator."

A dozen??? Hardly an extensive sample!

Well sounds like one should do the shotgun approach based on the lastest "expert advice":

1, buy a new battery
2. buy a new alternator
3. buy a new engine wiring harness

Or maybe ignore the hyperbole of some ( who did a Google search on regulators & alt.s and then
posts the same on Rennlist), or just take the car to a good Porsche shop!

"So, if I'm not an Electrical Engineer, how do I make sure a rebuild was properly done or that a new, rebuilt alternator was properly rebuilt?"

Again, based on this, take it to a reliable shop!

 

Thanks for the advice Loren but since I'm already up to my elbows in this, I will see it through. I'll let you know how this all turns out.

 

that was an internal melt down not an engine overheating, but nevertheless you are on the right path.If you do get it rebuilt nake sure you explain the problem well and that you have intermittent spikes. I agree with Loren in that you may never see the issue on a 30 second bench test.
I fortunately have a 30 year old 78 with an external regulator, just the brushes on the alternator, during my clean up of the car i took off the alt and took it in to have the bearings replaced since i had it out. Guy told me it was in fantstic shape and needed nothing but he put in the bearings for my anyway and cleaned it up .

 

Should you be speaking of me...

Back in the early fifties I was drilling out the rivets holding the cover on the old farm tractor voltage regulators so I could file down the relay contacts and get another year or so of use without purchasing a new regulator. Continued the same practice through the era of mechanical voltage regulators in my cars.

Yes, not a good sampling...I suppose I was remiss in not saying so as that was my reason for the disclosure.

 

So, what would make a ground cable fry like that? Negative battery cable coming loose?

WWest, don't sweat it. In my opinion, your insight is great, and the purpose of the board is to share your personal experiences. Otherwise, there would be no point to having a board at all.

 

not sure but it looks like that wire was carrying a lot of juice to ground, obviously unfused.

 

A reverse battery "jump" might do that.

But I still think it much more likely the starter motor remained engaged for a period of time with the engine running.

 

That hasn't happened in the 10 years that I've owned the car. So, it remains a mystery.

iceman, where'd you get your voltmeter? I looked in Cdn. Tire and a couple of other auto parts shops for a digital meter that records peaks and can't find one.

 

Replace with all fresh stuff,../alt/reg////then make double sure the wiring is in tact and healthy.

...piece of mind.

Best,
Doyle

 

I have a try RMS fluke for most testing , for my simple little meter I use in the car I got it at proncess Auto, again might not catch high rising spikes but i use it for monitoring overcharging. i also have a 60Mhz oscope so I kinda cheat a little to. If the spike is high enough you just might see needle deflection on a cheap analog meter , sometime that works better than a digital with a poor sampling rate.

 

I was hoping to find something that will record and save the peaks since driving with my eye on the voltmeter might be a little hazardous. Or, I'll just rig up a multimeter with alligator clips and tape it with double-sided tape on my dash - a ghetto voltmeter.

 

might work . High speed storage scopes are expensive. My Fluke 87 records mins and maxs but I am not sure about sampling rate.

 

Measuring the average voltage vs the peak of a DC voltage with an AC, ripple, content will be a function of the Analog-to-digital converter used as the "front-end" of the digital voltmeter. Putting a ~1 microfarad capacitor in series with the meter lead and using the AC range will always measure the AC/ripple content.

 

Happy ending today. I got the alternator back from the rebuilder, installed it and all is well. I suspect the voltage regulator was not replaced the first time. This time around, it was and the voltage is steady. Thanks for all the help. I am now a pro at removing and installing alternators. If anyone wants help in the Toronto area, let me know.