Turn it by hand forward and see what happens.
Agreed, pull the plugs back out & grab your 1&1/4" socket/breaker bar. Post what happens. EDIT After rereading I hope it is something external with the clutch (my guess) as opposed to something internal maybe with the thrust bearing (just thinking out loud).
Turning it forward by hand/1-1/4” produces the same result.
If I turn it back, and then forward, the motor eventually gets “tight” and doesn’t turn anymore.
The block was line honed, and when I assembled it, I rotated the crank every time I installed a piston. No binding at all.
