The starter lagging or cranking the engine over slowly very well could have been because the starter needed a rebuild. Assuming that no wires are burned up in the starter about all there is to it is a commutator and a set of brushes. Unless the starter has a life time of starts and stops on it, like in a package delivery situation the brushes probably aren’t really worn down completely, remembering that unlike the generator the starter only turns over a few times every time you drive it. So in reality assuming all of your connections from the battery are solid you can usually narrow a weak starter down to a problem at the commutator. If the commutator is not worn but just oxidized or covered with burned oil a good cleaning and sanding/stoning will generally bring the performance back to normal.
Just changing out the cable generally gives a fresh clean path for the current at the connections. Again, my point is, if you have a properly rebuilt starter motor, and a good solid #1 or even #2 cable and CLEAN connections your 6v starter is going to perform up to par. No need for monster sized battery cables.
I think the myth about better performance after changing to a 2/0 or 4/0 cable is due to the fact that in the process of changing the cable they re-established a good lo-resistance connection. As Jerry brought up, the connection at the lugs needs to be solid, if the lug is simply crimped then moisture gets into the joint and you loose continuity between the lug and the copper wires due to corrosion. This creates resistance at the joint and you begin to see a voltage drop at this point. The more voltage dropped across the connections the less available to the starter and the slower it will crank. Again, as Jerry points out a soldered lug is definitely going to give you better performance over a longer span than simply crimping the lug.
Denny Graham
Sandwich, IL
