slow cranking 351w

[TonyMadrid]

I have a hotrod with a 351W and an AOD trans. Last year, at the end of our cruisin season, the engine began giving me cranking problems. It would crank really slow at times (whether it was cold or hot). I checked my battery and it was strong and fully charged. I then installed an aftermarket starter but the problem persisted. This season I installed a Powermaster high torque starter and it seemed to solve the problem, but only momentarily as the problem began again. However this time the starter will sometimes just spin (free wheel) without engaging the flex plate. I have to turn the engine at the crank pulley with a wrench and then it will crank and start.

I pulled the flexplate inspection cover and examined the teeth and they were all intact.
I have checked all wiring and cable contact points to insure good connections and good grounding. I have even replaced the starter solenoid.
The problem is still present.

One thing that I did notice is that when the starter free-wheels and I have to turn the engine by hand, it seems very difficult to turn. The engine is not a high-compression setup and I know it should offer some resistance as the plugs are still in, but from experience it does seems much too much difficult to turn by hand.

It seems that there is something causing the excessive resistance and not allowing the engine to turn freely and start. I don't think it is anything internal, i.e., timing chain, crank, rod, or cam bearings as I would think any issues such as those would have been noticeable with either noise and/or performance. However, once running, the engine runs fine and performs well

Yesterday while at a cruise, one of the guys mentioned that he had heard of slow cranking situations that were caused by torque converter and/or flex- plate problems.

Today I am planning on pulling the plugs and see how that impacts hand cranking. I also plan on separating the trans from the engine to see if there are any obvious flexplate or converter issues and while separated see if the engine hand cranks easily.

Any thoughts or help would be greatly appreciated.

Tony