So I'm having problems with the starter system on my '37 8cyl. Here is the initial scenario:
After sitting for a while, or initial start up, the starter turns the engine over fine and engine starts. If it is quickly shut off, or if it is driven and then shut off, and tried to restart right after shut off it will weekly wine and not even turn the engine over.
On the second attempt at starting I noticed on cranking the voltage drops from 6.4 to almost 2v. Bendix gear engages and will turn the crank only about a 1/4 turn and stop. Once the turning stops the solenoid will begin a light smoke. For comparison on my '37 6 the voltage drop on startup is a little less than 1 volt, and starts strong and isn't weak at all and will crank all night long.
Initial thought was weak battery, but battery is fully charged and does indeed properly charge when the car is running. 6.4v, generator charges at about 8v when running. Also when car is hooked up to a battery charging unit in the garage the same problems continue.
So I tested cleaned and tested all the terminals, grounding surfaces, etc to make sure everything has continuity. All was fine. To be further sure I ran a ground from the starter to the battery directly avoiding any possible losses in the other cables, wires, etc. no difference.
Next I changed the starter solenoid to a solenoid off of my '37 6 (which I know for sure works fine). Problem persists. Starter turns, engages, stops.
So I changed the starter itself to a spare I had that was rebuilt and tested. and I tried just a direct connection to the starter itself avoiding the solenoid all together. Still the problem persists, starter will turn engage and stop, and the drop is 3-4 volts.
I put the solenoid back on, connected it that way. let it rest for about a half hour. Pushed the button on the solenoid and starter turned engaged and turned the motor over and over and over. Then started to get weak and I let off the button. I tried turning it over again and problem returned. The starter engaged, stuck, and solenoid began to smoke.
My next thought was that maybe this starter as well was actually bad.

Any thoughts? Are the starters the wrong kind for an 8? Have 0 problems with the starter on the 6 connected the same way.