Using 12v on 6v system

Barber31

Barber31

Well-known member
My 6v battery is not putting out enough power to crank over my engine. I thought it was a grounding issue but a friend mentioned it could be that my engine is still too tight from the rebuild. So I've been using my 12v jumper box to crank it over. Is there any issues that could arise from doing this long term like say to the starter or gen internals? It seems to not have any effect on my wiring or blowing my fuse.
 
Is it tight when turning by hand with the plugs out?
Make sure the starter bolts are not to long rubbing the flywheel if the motor is hard to turn by hand.
Crank it with the starter and key off to eliminate timing issues
 
Can you safely pull the vehicle to start the engine by engaging the clutch while the transmission is in 3rd gear? Just cycling the engine over will allow it to limber up enough that a charged 6v battery should be able to start it. I agree that a fresh engine should not be that stiff but depending on how tight the Babbitt clearances were set, this could be the problem.
 
Sounds like you've started it on 12 volts and probably have some minutes on the engine now. It should be loose enough by now to start with a GOOD 6 volt battery. As mentioned, it sounds like your engine may have been built a little on the tight side, or the battery could just be a little on the weak side. I like to let a rebuilt engine run a few minutes at idle or fast idle, then let it cool to room temp, then run it a few minutes again and let it cool to room temp. Do this several times until you feel the engine has loosened up enough to hand crank without breaking your back.

As far as jumping with 12 volts, yes, you can do damage, but by using light gauge cables and only connecting when the starter is engaged will lessen the possibility of damage. I threw a starter winding in my 1952 Studebaker when I jumped a weak 6 volt battery with a 12 volt battery. You can also buckle the battery plates. And don't make the last connection at a battery post, or you could blow up the battery.
 
Well in that case it's not a tight engine. Must be what I thought to begin with, poor connections. I overhauled the engine myself and I set the clearances to the specs in the red book. And I have put a few miles on it now so by what y'all are stating it should be loosened up by now. When it was on the stand I could crank it with a medium length ratchet so I guess that's another clue it's not too tight. So where should I check first? With the 6v battery alone it doesn't crank but maybe one revolution but with the 12v jumper box it spins extra fast. So maybe it's not poor connections? Maybe just a bad battery?
 
You should put a 3 to 6 amp charger on the 6 volt battery for at least 4 to 8 hours, then use a load tester to check the battery condition. Or you could put a volt meter on the battery while you try starting the engine, but for best results you should also put an ammeter on it at the same time, so you can check the starter draw. My thoughts are you just probably have a weak battery.
 
Battery problem....

Back in my High School days I rebuilt the engine in a '50 Ford. Flathead V-8. Had the same symptoms: wouldn't start on the 6v battery in the car. I figured it was just too tight from the re-build.

I'd park the car at school outside the auto shop and borrow the 12v battery they had to start the car with jumpers when it came time to go home.

At home I would park the car out front of the house where I could coast down the hill to start it when I had to go to school.

Until one day I had to borrow a 6v battery from the shop and it started the car just fine!

Next day I convinced my Mom to buy me a new battery and all the problems went away! :)
 
Good news. The test revealed it was a bad battery and I replaced it and all is good. Thanks again fellas.
 
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