bad alternator = rough running ?

riverbend · Dec 2, 2021

I have a Farmall 350 that has been converted to 12V with a Delco 10-Si alternator. I was digging some dry beans out of the weeds with an AC 72 combine and the tractor was running rough. Wiping out the distributor cap and polishing up the points didn't help much.

I shut the tractor off to cleanout the combine and it wouldn't start, deader than a hammer. Battery voltage was about 12.7V but the battery is about 5 years old. Tractor fired right up with a jump.

Checking the battery voltage on DCV, it was all over the place, 0-19V, no steady reading. Checking on ACV, same thing in the 10-17V range. I'm guessing the rectifier pooped out and the coil is not happy with AC. Does that make sense ?

If so, what is the current thinking on alternators, as in reliable, compact and easy to install ?

Thanks
Greg

old · Dec 2, 2021

Sounds like you have a digital VOM and they don't work well around a running engine. I'd check your spark and make sure it is a good blue/white and jump a 1/4 inch gap at the center wire of the cap and at all the plug wires. Also make sure you have a good steady flow of gas from the carb drain plug

Bob M · Dec 2, 2021

Low system voltage can indeed cause rough running. And it will ultimately shut down the engine as the battery goes flat.

You need to check system voltage with an ANALOG voltmeter (old school needle-type meter). If the alternator is charging you will see 14.0 - 14.5 volts across the battery with the engine running at half speed. And if the battery is good and charged, 12.6 volts with the engine shut off.

Before you get in too deep, check the battery cables and terminals, especially the ground connection to the frame. Also check the alternator wiring and make sure the idiot light/resistor/diode (can be any one of the 3) has not failed.

If it turns out your alternator is bad, recommend you stick with a 10-SI. They are rugged, inexpensive and available pretty much everywhere.

used red MN · Dec 2, 2021

I agree with all those attributes of alternators. Does your alternator pass its current through the original ammeter if so it should show a heavy charge after the tractor dies and needs jumped. If for some reason the ammeter was bypasses a quick way to tell if the alternator is putting out at least some charge it to hold a metal object like a screwdriver blade against the bearing cap on the back of the alternator in the center while the engine is running. If it sticks to it you are at least getting some charge. On a side note your tractor was likely 12 volt positive ground when new. When the alternator was installed the connections to the ignition coil should have been changed. The wire feeding the coil from resistor block ..fed by ignition switch.. should now connect to the plus terminal. And the negative terminal should connect to the distributor.
Edit to correct some wording.

This post was edited by used red MN on 12/04/2021 at 09:04 am.

cuby · Dec 3, 2021

I worked om a gas 2510 JD once with similar problems. Did the tuneup thing with not good results. changed out the alt. and all was well.

old · Dec 3, 2021

Its rare that an alternator would cause and ignition problem since there to different circuits unless the alternator was grounding out the whole battery system

wore out · Dec 3, 2021

(quoted from post at 15:57:10 12/02/21)

ASSUMING it has a "good" battery", fully charge the battery, disconnect ALL wires from the alternator, start the engine and note if there's any difference in engine operation without the alternator operating.

Also, if this is a (-) ground system the (-) primary terminal on the coil needs to be connected to the distributor.

riverbend · Dec 3, 2021

Okay, you guys are the best. Disconnected the alternator and it ran about the same. With the alternator disconnected the voltage at the cable on the starter was still jumping all over. The voltage on the battery terminals was steady. Moving from the negative post to the chassis the readings were all over the place again. Loose cable connection at the rear of the battery box.
Thanks for the help
Greg

old · Dec 3, 2021

Funny how a poor connection can cause odd problem. Vibration also comes into play so a bad connection plus vibration equals odd problems

riverbend · Dec 4, 2021

No kidding. A loose wire on the ignition switch on my H gave me fits. It would throw a 1/4 spark from the coil wire to the bolt in the oil filter housing but it would not fire. That one wasn't vibration, it's a new style ignition switch and I kick the wires with my toe.

bad alternator = rough running ?

riverbend

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old

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Bob M

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used red MN

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cuby

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old

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wore out

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riverbend

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old

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riverbend

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