Can I lose polarity?

[JSabah]

My ‘49 has been converted to 12v. It was one but last night after a short drive my 1 yr old battery was dead. I suspected the generator (yes I elected to keep my originality) it the regulator. After reading other threads, I started my testing. 1st the residual voltage in the gen. ... I had 1.2v instead of the .5-.75 expected. So I re-flashed/polarized the generator - flashing the Arm terminal while the regulator was disconnected. Thought I’d check out the car and wallah- the amp meter now shows as it should (turn key/discharge; start car/ charge; let it run/slight charge).  Went on to do a get more things/cleaning the engine bay and 15 minutes later I start the car and the amp meter shows that it isn’t charging. I find it strange that it worked after flashing then stops... can I loose polarity? Where do I go from here?

[Tooljunkie]

Check regulator. And grounds , battery and engine/body grounds included. Bright and tight. 

[JerseyHarold]

If it's still a mechanical voltage regulator, I'd try smacking the VR by hand with the engine running when it's showing a discharge.  If the ammeter shows it's charging again, I'd change out the VR.

Edited October 18, 2020 by JerseyHarold

[JSabah]

I gave the BR a tap. Didn’t seem to do anything. Thien I swapped out the VR with one from another car I just started working on - but I don’t know for 100% that it is good. Car didn’t charge unless I flashed it again and then only temporary again. 
 

disconnected the F and Arm terminals, jumped the two and checked voltage with a voltage meter..... nothing (but don’t forget that the amp meter had previously shown a temporary charge ... before it didn’t). 
 

I don’t understand why it would temporarily charge after flashing... is it even possible that a generator to work intermittently? 
 

BTW all grounds are clean and good

[JSabah]

Could this be the issue... watch the crankshaft pulley