SBC PROBLEM!!! Ran but now wont turn over by hand...

[81cutlassSBC]

Im at wits end with tryin to figure this out... its an 86 SBC engine 355, turbo 350 trans and a stock ten bolt. Motor has a thumpr series cam in it with world sportsman class 2 heads on it and has been decked with 12-1 compression. Has an edelbrock performer intake and a quick fuel 750 carb on it. Has a turbo 350 with reverse manual valve body 3500 stall shift kit etc.
Now as for my fueling situation I bought the car with this engine in it and at the time it had a 950 holley with no choke on it which I felt was a bit much so I swapped it out for a 750 quick fuel carb with electric choke. I've been tinkering with the car a bit to get it ready for spring and on the first halfway decent day we had I took the car for a spin only to find the car spitting and sputtering pretty bad and when I shut the engine off it turned itself backwards so I assumed the timing needed to be redone. I pulled the distributor out AS WELL AS the spark plugs and went to turn the engine over with a ratchet and socket on the crank bolt only to find that the engine wont turn over... At first people were freaking me out saying the motor was junk because someone didnt put main caps correctly on or pistons in backwards etc. But Ive talked to a few other people who say if that were the case the engine wouldnt of ran fine before... I bought the car in a storage warehouse drove it outside and around the block a few times and it was fine. Then trailered it home where Ive been messing with it since and this was the first time I drove it since buying it and since changing the carb but it ran n drove fine originally with the 950 on when i bought it. It made no bad noises from the engine or anything and was running about a half hour before I pulled the dizzy and plugs out of it so Im at a loss with how I can turn the engine over to reset my timing at TDC. The crank bolt just keeps getting tighter and tighter... HELP PLEASE!!!!!!!!!!!

Also just a side not if I bump the key to crank it the motor rolls over fine.... Just cant set it to TDC that way

 

[Pontiac455]

Make sure the ac compressor or the ps pump or water pump or alt arnt seized holding er back. Also check to see of the starter is disengaged. I have a 434 with 13-5-1 comp and can turn it over by hand with all the plugs out.

 

[darbysan]

Be careful turning the engine using the crank bolt. If you tighten it too much, you can break that bolt. Then you have a heck of a mess to fix.

 

[CamaroAdam73]

You can use the flexplate/flywheel to rotate your engine, everybody always forgets about that lol. Use gloves.

I would take everything belt driven loose like pontiac455 said, one of the belt driven devices could be holding it up.

But to be honest with you, it doesn't sound like you drove it enough for a problem to present itself fully, you should be able to turn that engine by hand. I've turned a 14:1 race engine by hand, it was hard but you get the point here.

Also i would drain your oil into a CLEAN pan and check it for metal shavings and fuel contamination, if all is well just re-use the oil if you didn't need a change anyways.

 

[CWPottenger]

By reading your post I would seriously look at the starter. If you have all the plugs out and you can't spin motor with zero compression(no plugs), but the starter can, then odds are the starter is actually stuck engaged to the flexplate. A stuck starter can cause engine to backup when turned off also, and would have a whine when running.