[Ogre]

First a little background.

1971 Lemans 350 2 bbl engine ... will be installed in a '72 Lemans. Taken apart and cleaned up a little, new cam bearings and cam, new valve springs, new push rods, new lifters - all as close to stock as can be.

The engine is on a test stand. Been running it occasionally for over a month until I can get the garage space to install it and start to convert the auto to a manual trans. Recently moved the HEI Distributor around 1/8th turn and rotated the plug wires, so I can get to the adjustable vacuum can to get some of the "high" advance out of the timing.

Started it today, and got the timing set, and the vacuum advance lowered and it runs good. As I revved the engine got a little squeal from the fan belt - no problem. After I released the throttle, I had a very slight squeal (coming from the fan belt around the alternator pulley). Glanced at the voltmeter, and it got over 16 (approx 17-18) volts. As I revved the engine, the squeal got louder and the voltage stuck about 18.

Now when I start it, it shows 12.5-13 at idle, no squeal. If I rev it, the voltmeter goes to over 16, and the squeal starts again. The only way to stop the high voltage and squeal is to shut it down.

Bad alternator (it's a reman AC Delco 78A)? Something electrical trying to pull more electrical power causing the alt to "load up" and become hard to turn? HEI demanding too much power? What do I need to check next?

Remember, it's a bare engine with no load except the battery connection to the HEI, and everything has worked fine until today.

I'm confused - thanks,
Ogre

[sleepy]

The voltage regulator is bad. try another alternator and see if it does the same thing.

["QUICK-SILVER"]

Check the wire going to terminal 2 on the alternator. It's the voltage sensing terminal for the regulator. No or low voltage on it tells the alternator the battery is dead and it will charge all it can to fix it.
AND the regulator itself might be bad and cause the same thing to happen.

Make sure nothing metalic has gotten in the back of the alternator. There's a 'D' shaped hole in the back with a test tab on the regulator in it. If you ground out the test tab, the alternator charges wide open.

[Ogre]

Thanks for the feedback guys. I assume you are talking about the "internal" regulator in the alternator?

I was going to swap out the alternator, but this one in the pic is the only one I have on hand.

It came out of my '72 Convert, and I think George (Kujanski) told me that it needs an external regulator (that was Loooong ago, so I'm not sure). Will this one work and is the R and F, 1 and 2 respectively?

Do alternators just go bad? As I said the charging system has worked great for over a month, and the only change from last week is I rotated the HEI, and moved the plug wires.

Ogre
BTW, terminal 2 is Hot (12.5 v) to the battery, and there is nothing in the "D'" shaped hole in the back.

[stellar]

Over charge on internal alt---- Reg or alt like sleepy said-----S wire like Quick-Silver said---bad ground or bad battery are the only things left.

[stellar]

You snuck that in there while I was typing. That is an external reg type alt, as George told you. No S wire at alt or way to grnd thru D hole. Every thing else still applies.

[sleepy]

If the regulator goes bad(this can happen ANY time) it will either lock open or closed. Over charge or not charge. sometimes under charge but that is a sign the alternator or regulator are getting weak.

["QUICK-SILVER"]

Yes, the one in pic is external regultor type, not the same as the one you're using.
Terminal 2 (R) is further away from the battery stud on back and is suppose to have battery votage.
Terminal 1 (F) is the excite wire, only suppose to be hot when running, OR have power coming to it through the idiot light when switch is on.

And yes about the alternator having to be grounded good. (forgot about that one)

Internal regulators fail for no known good reason, other than being a transistorized part that doesn't take much to kill them. Like shorting a hot wire while it's charging.

Moving the distributor had nothing to do with it.

[george kujanski]

Ogre, if the alt in the pic is the one you are using, you definitely need an external reg in order for it to work correctly.

DO NOT connect anything to the R or F terminals. You probably have the battery connected to the F term, and that will cause the alt to go to max output.

The R and F terms are used with the external reg.

George

[stellar]

Good call George. Delco 78 amp should be 12SI. Got to go to hospital now. Just got a brand new baby grandboy. #6

[Ogre]

Originally Posted by stellar

Good call George. Delco 78 amp should be 12SI. Got to go to hospital now. Just got a brand new baby grandboy. #6

Congrats Stellar !!!

George, I just pulled that out of the box on the shelf. It's the one I took off of my '72 Lemans Convert, that you told me would not work (about 2007 sometime) since the PO had removed the regulator.

Anyway, I didn't put it on my project engine. I'l get another 10si 78 amp tomorrow, and see if it works ok. My concern was that if I am just eating up alternators because of another problem, I didn't want to keep destroying them. It gets expensive after a while!

This is the engine that you helped me with the diagram for a "make-shift" harness to get it running and keep the battery charged.

More tomorrow,
Ogre

[Ogre]

Ok Guys, got the new alternator on the engine, and started hooking up the wires (before connecting battery).

The instructions say that #1 terminal MUST receive voltage. Does it really have to? Could this be the reason my other Alternator failed? Terminal #2 is wired directly to the positive of the battery, so it is "hot" anytime the battery is connected.

Remember that this is an engine on a test stand. It doesn't have an idiot light. George (Kujanski) corrected my crude, rudimentary wiring diagram and I just disregarded the idiot light circuit, since I don't have one. Should I "gerry-rig" one up, or can I safely (defined as = not destroy the alternator) run the engine without that circuit? BTW, my voltmeter is connected to the ignition switch "ON" ("ACC") position direct to gnd, so I get the battery voltage when I turn the ignition key to on.

I know that it will run and keep the battery charged (it has for probably 15-20 engine runs) with no problems.

More advice please, before I connect the battery and do another engine run.

Thanks,
Ogre

[george kujanski]

You can wire the #1 terminal to a switched ignition source; same place you have the voltmeter connected.

Without term 1 connected, the alternator may not "excite" until you rev the engine a bit. With the term connected, it'll start charging as soon as it's shaft speed gets above 1100 or so (about 500 engine RPM).

IIRC, on Delco alts if term 2 (sense terminal) is not connected, the alt will shut down. It's a built in safety; if term2 has no voltage, the internal reg would otherwise crank up the output voltage to max, frying all the electronics.

George

[stellar]

you can excite the alt with a test light. Bat --- lite---terminal #1 It only takes a moment to excite it. Once it is charging it will continue to charge till the alt stops spinning. It will charge even if you take the test lite off and will not harm the alt.

[Ogre]

I went ahead and soldered up an extra bulb that goes in the dash circuit board for idiot lights, turn signals, etc., and attached it from #1 to the "batt" on position on the ignition switch.

After connecting the battery, I turned the key on, and the light shined brightly. I just have to remember to not let it ground out on the block.

Now, if I can move my wife's car out of the way, I can roll the engine to the garage door and point the tailpipes out and run the engine. But I'm not concerned about that, since I already know that it runs well. One pump on the carb linkage, and it fires right up.

Thanks for the help on the Alternator guys ...

Ogre