Ok guys this is my first actual post here so bear with me if its a little long. Ok so I have a RHD 87' fc3s manual transmission turbo Japanese model. I'm stationed in Japan for now but going to bring the car back to the states. Moving on, I had to replace a rotted out freeze plug on the back of the engine behind the flywheel because it was leaking antifreeze and running hot without the proper antifreeze level. I replaced all four freeze plugs to be on the safe side incase another decided to give me problems down the road. Now when installing the flywheel back onto the engine with the clutch and clutch plate attached it was rotating just fine with no transmission installed. Now after installing the transmission and going to start the car the stater engages but it wouldn't spin the flywheel, I removed the starter and bench tested it with a spare battery and it works just fine. When I try to turn the engine via the front main pully (any other car would be the crankshaft pully but I guess it's called the E-shaft pulley on a rotary??) I could not turn the engine from this bolt with a good amount of force, then I moved to the back of the engine and tried getting a pry bar inbetween the teeth of the flywheel to spin it and no luck it's not budging. Like I said, before reinstalling the transmission it moved just fine. Any thoughts on what could be making the flywheel/engine not turn? Yes it's in neutral and when in neutral the rear wheels spin just fine and the driveshaft. I tried moving the flywheel with it in neutral, clutch in/out, with no luck. Any help would be greatly appreciated

 

Sounds like the splines on the input shaft didn't line up properly inside the clutch, or the input shaft bearing is wedged and not letting it turn, or both

Either way you gotta drop the trans again

 

Yeah hopefully it's something simple like that, I just hope no damage occurred that'll hold me up even longer.