I was going to do this 6-8 conversion once but instead upgraded to a 1 wire 12v alt because the battery salesman advised that the 8 volt battery would have a short life because it would never be fully charged to 8 volt by the 6 volt generator.
That's pretty good knowledge for a battery salesman. Most 6 volt generators will put out about 7 volts - just like a 12 volt generator puts out nearly 14 volts. The part about the shorter life is more debatable, because it depends on the quality of the lead alloy and acid.
There is another way to go with a 6 volt system. They can be made to work. The trick is to reduce the voltage loss throughout the starting system. People won't believe it works as well as it does until you do it You are already one step ahead of the curve by having a mag instead of a 6 volt coil.
The next step is to get a really good 6 volt battery. Lots of Amp hours. See if you can find one that weigh 50 pounds. Odyssey used to make one..... maybe still does. It won't be cheap, but everything I am going to say next beats the pants off an 8 volt system. Performance & price both.
Start with that darn good 6 volt battery and next we simply go through that 6 volt system on a mission to reduce voltage loss. Every one of these things will be a benefit
1. Now we do the new battery cables. Make the battery cables out ofwelding machine ground lead wire with lots of copper strands. Make the cables as short as possible, You may end up using much larger diameter copper wire for the battery cables as now, use flexible multi-strand (high dollar) wire you can buy it by the foot from the welding shop. Maybe you can get your cable ends there too. Get pure copper everytime you can. Clean, clamp and then solder the ends on - you probably can't solder at the battery end of each cable but make the best connection there that you can. Where the ground wire connects to the frame of the tractor you should scrape down to bare frame metal. Even run a jumper wire from the frame ground right over to the bolt that holds the starter to the frame.
Now go into the starter solenoid - it rides piggyback on the starter motor, and comes apart with a couple of obvious screws. Basically a tin can with a coil and contacts insidel Take it apart and polish up the big copper contacts inside. Leave the rest alone.
Next is the starter motor. Make all the contacts clean and bare metal. Either take it to a vintage car master starter rebuilder or do it yourself. Re-cut, clean, and polish the armature for full 100 contact with the new brushes. Bushings and renew connections everywhere. Don't forget to re-polarize it. Every vintage car club guy knows someone who does all this.
The reason to do all this detail work is simply because a connection that isn't perfect is a source of voltage loss. And you cannot afford any voltage loss when you are only starting with 6 volts. That is all the 8 volt battery system did - it simply offset the voltage loss. You can do the same by lowering the resistance througout with that level of attention to detail. Using larger battery cable, larger battery, and honest metal-to-metal connections.
It may not work. But if it doesn't going to an 8 volt wouldn't have either.
As a final touch, put a voltmeter across the battery terminals when it is running and make sure the generator is charging at somewhere between 6.1 and 7.2 volts at anything between a fast idle and full PTO RPM.
Good Luck,
rScotty
