OK- - - -now we're making some progress. That's way too HIGH a voltage reading for a starter that's under cranking load. Was the cranking speed normal, or slow? If the cranking was slow, there's a high resistance circuit inside the starter. Remove the starter and dismantle it. The first thing to check is the mechanical push button that the foot pedal linkage operates. It's attached to the starter housing with two screws. There's a big copper contact at the stud where the battery + cable attaches, and another one that connects to the field coils and armature brushes. The push button connects these two contacts with a big copper washer. Burned contacts there can cause low current draw, or there could be loose or burned connections inside the starter.
Unless you find problems with the bolt-on switch, it's probably time to rebuild or replace the starter. Be sure to get a 6 Volt starter if you replace it, since there's a gear drive and flywheel tooth difference in 6 and 12 volt units. There's at least a possibility you've got a 12 volt starter installed. The quickest way to tell the difference is to measure the diameter of the armature shaft- - - - -12 volt starters have a 1/2" diameter shaft- - - -6V armatures measure 5/8". If there's a Delco ID label on the starter, a 6V label will have black lettering. 12V labels are red.
If you've got a 12 volt starter, the next thing to check is the number of teeth on the flywheel. 6V flywheels have 139 teeth. 12V flywheel ring gears have 168 teeth. a 6V starter WILL NOT work on a 168 tooth flywheel- - - - -there will be lots of noise, and rapid wear and/or breakage of teeth on both the flywheel and the starter drive.
Jerry
