I don't think an 8v would damage the starter but it's not wise to use one. If a system is properly maintained a good 6v battery is all that's needed.

@tiny 

Completely agree

Every 6 volt system I have cranks just as well as my 12 volts, and in fact better than some of the 12's.

I can't really even say I find that my 6 volters need any more maintenance than the 12's.

You gotta keep them all clean.  🙂

So...

Why push your points and coil, gauges, and bulbs that hard if you don't need to?

@ole-olson TY...

Well I may have come to answer, my 6 volt starter just died on 8 volts!!!

In that case I suspect the starter may have been faulty to begin with. I have converted a 6 volt tractor to 12v with the exception of the starter, it didnt fail in the 5 years of use after but the tractor never failed to start and when it was warm would idle slower than when cranking.

Tony

@anthony-williamson I think I may have turned it over to many times each time I tried to get the car to fire and it overheated.

That will cause it though with the 1 I used on cold start it did take a few turns to fire.

Tony 

Hi,

Just seeing this forum, a 6-volt starter will run fine on 8 and 12 volts. 

I would suggest adding a voltage reducer resistor on any sensitive electronics on the car (Fuel Guage, Radio, etc). 

Light bulbs will most likely wear out sooner but if the car isn't driven with any frequency perhaps it's not a deal breaker. 

I would pull the starter to check the brushes, Bendix and the starter solenoid if you have one.

Best of luck!

I will second that a well charged 6v system will do just fine.   

I just added a battery tender to my '41 and the difference was night and day.   I believe I've been undercharging for a long time.   I'd get decent cranking but since I added the battery tender, it's so much faster.   I guess I need to dig into my regulator a little more.

Not sure if this is true or not but I was taught this when I learned to drive and have always followed it.  When cranking a car over at most crank it for 10 seconds.  For every second you crank wait twice that for it to cool.  Was told that way the starter is far less likely to be damaged by overheating.  I find myself counting in my head when I turn a key if it does not fire the first time out of habit now.  

Speaking from experience. I put an 8-volt battery in my '32 coupe a couple of years ago. The starter definitely turned over faster and therefore it did start a little quicker too. Here's the problem I found. The 6-volt generator can't keep the 8-volt battery fully charged. After a while the battery just went dead. I'm no mechanic so I don't try to explain this but I put a 6-volt battery back in and it starts just fine. I do keep a tender on it. I also found that the more I drive it the easier it starts and the better it runs. I've put about 60 miles on Lucwheel in the last 3 weeks driving to 2 different shows. It is so rewarding and satisfying to fire her up and take a cruise around the neighborhood.

I had a 49 GMC that an old mechanic put a 54 engine in it. He said it should have a 12 volt but if I use an eight volt battery then I would not have to change things to 12 volt and it would start it good . The only problem was I had hard time keeping the regulator adjusted right. too much juice to battery then i would burn out head lights and not enough then battery would not have enough juice to start it. Otherwise everything else worked good

8 volt batteries are a band aid to a problem.  6 volt systems work fine with clean connections and the proper sized cables and wiring.

@dunfire I completely agree with Patrick. Using an 8 volt battery is treating the symptoms instead of the disease. I have a good "electrical Guy" and all my 6 volt stuff works as intended.

Mike