ya say its original?. so must be 6 volt..?? and just turning the starter with a battery charger probably wont have enough amps to pull much of a load. The best way is to crank it and see what kind of amps the startin is pullin to know if engine is tight, or starter is draggin. Your six volt battery charger is probably not putting out enough amps to really test the starter, but id think you couldnt stop it with your hand unless its only putting out a 6 volt trickle charge, then you probably could.
Id say jump it with 12 volts to try it, it wont hurt anyting, just dont turn the lights on while jumpin. Those old 6 volt starters dont really spin (like a modern 12 volt system) anyway even if everything is good.
