Jump Starting a 6 Volt off a 12 volt

I have a 1950 John Deere M with the original 6 volt system and it starts hard.
It has a good battery, new battery cables, a rebuilt starter, new points condenser rotor and plugs.

I have jump started it in the past off a 12 volt system and question if doing this is damaging the system in some way.

Thanks in advance for advice

I ran 8 volt batteries in my two old forklifts (towmotors)..never had any problem...the 6 volt batteries didnt have quite enough power..also wore out faster.Got my 8 volts from tsc.

It does no harm to the starter. Most I see converted from 6 to 12 retain the 6v starter. When the regulator sees more than 7 or 8v,it should isolate the genney and prevent damage to it. If this is an ongoing problem it would be smart converting to 12v. It can be as easy as disconnecting the genney,installing a 12 v battery and changing ignition coil or putting a resistor in the coil feed. The tractor will go all day on a single charge and still start.

It may or may not damage the "system" depending on where it was made HOWEVER it can damage your eyes or some other part of you if the battery explodes!!!!!!!!!!! Can happen if 12 volts is jumped to a 6 volt battery especially right at its top where explosive gasses and a spark take place !!!!!!!!!

NEVER NEVER make such a 12 volt jump right at the 6 volt battery which can possibly make the battery explode!!!!!!!!!

If you must make such a jump I would (if possible subject to starter switch or solenoid and location and accessibility) just jump the starter ONLY. If it had a switch or solenoid that has an open easy to get to terminal on the starter side (NOT big cable from battery side) you can jump it there and frame ground. If it does NOT have a switch (like a saddle mount mechanical switch where starter post is underneath and you cant get to it) or solenoid where you can get to the starter post this method IS NOT AVAILABLE. Of course (well DUH) the ignition must be on and the tractor battery have sufficient energy to power its ignition coil so a spark develops.

NEVER make a last connection (makes sparks) right at the battery as that's where explosive gasses are !!!!!!!!! You can make the first ungrounded post connection at the battery but then make the last frame ground connection down away from the battery........

If you do a jump BE SURE TO MATCH THE BATTERY POLARITY + to + and - to -

Sure, Ive jumped a 6 volt tractor off a 12 volt source as have many others but I NEVER made such (last connection) at the battery top but on the frame elsewhere and if possible I jumped the starter ONLY if it had a switch or solenoid that made such possible BUT I JUST CANT GO ON RECORD RECOMMENDING IT so do it at your own risk

John T

Seen this posted a couple times .. not tried or proven yet , but how about forming a lead rod that could be suspended above the plates in the 12V battery in the 3 rd cell of a 12V and jump from there onto 6V jump?
.. if more needed go to the 4th cell making an 8 V jumper ?? Just wondering ??????

First thing is that sounds an awful lot of trouble to go through for a few seconds of utility.

Second thing is where do you get the lead rod?

A battery charger applies AT LEAST 12V to a 6V battery on "fast charge" mode, so the voltage itself is not really the issue.

It's the spark in the proximity of the hydrogen-producing battery, as John T indicated.

Connect your 12V at the starter if at all possible, and don't leave it on there once the tractor is running on its own.

The charging system is what you have to worry about. If it were me I would remove and isolate the generator wires. They are easier to get to than the cut out relay.

You might want to check your timing. SPARK in the center of the timing window at full throttle and TC/DC at low idle.

My Father used to do that a lot, the only problem I can remember was the back cover broke on a JD MC starter. But really, if you are not trying to start it below 0f it should start fine with 6 volts, you have a problem you haven't found yet, keep troubleshooting!

Keep in mind that a slow turning starter is characteristic of a 6-volt system. What you see as hard starting may actually be a normal condition. That is among the reasons that most automotive and tractor applications moved up to 12 volts over the years. I still have a 6-volt car, and it turns slow, but always starts.

I have a JD MT. Same problem until I MADE my own battery cables. Take a jumper cable and add it to the Neg Cable. Between tractor Battery and Starter. You could do the same with the Pos ground. See if that helps.

Like JohnT says,just jump straight to the starter and avoid the battery all together. You're tractor is probably positive ground isn't it? Make sure the vehicle you're jumping with isn't touching the tractor,then hook your positive jumper cable to the frame and touch the negative to the starter post.

Yes but if you create any sparks with the cap open you'll be scraping battery acid off the brim of your hat.

No need for 12V jump starts. A gasser doesn"t need high rpm cranking like a diesel to start.
As long as the mixture is correct and there is a strong spark at TDC. Cranking rpm doesn"t really matter.
Sounds like too low voltage at the coil to spark the plugs.
Either the battery CCA is too low. A too high current drain on the electrical system that is dropping system voltage. Or there is voltage drop in the connections and/or wiring.
Wouldn"t be the first time either Finding a 12V coil in a 6V machine . Or the coil polarity connected backwards.

Well if you have to get another vehicle around to jump start, you may as well just use that vehicle to pull start the M. No worries about nothing then.

Get the starter fixed andmaybe some new 1ga cable 12v getting thru to your regulator wont do it any good remember it started when new so if everything is in shape it will start like new again. That is also a good way to blow a batt not a good idea using 12v on a 6v system.