Motor won't turn

[Datsun AshLee]

Hi everyone, I pulled my motor after it blew the head gasket, pulled the head and there was water on the top of a couple pistons, cleaned off a little rust on the cylinder walls. We then put a new gasket and head on, put it back together and then tried to turn the motor to adjust the valves, but it won't turn. I pulled the motor again, put the block on a stand, and pulled the oil pan to look for parts that were maybe rusted together. Everything looked good. Anyone have an idea?

[JT68]

Was this engine running when you put the other one in? Or had it been sitting a long time, or unknown?

[greydog]

When you say "tried to turn the motor over". How were you doing it? Plugs in or out? Using the starter, a ratchet on the crank or a breaker bar with a 3' cheater?
If it had been sitting for a while, the rings tend to sort of want to "stick" to the walls.
Pull the plugs and squirt a tablespoonful of thin oil in each cylinder. Id use Marvel Mystery Oil or ATF.
Let it sit overnight.
If the trans is still attached to the engine, make sure the trans is in neutral.
Use a breaker bar and "rock" the crank pushing clockwise, then counterclockwise like you are trying to wiggle something loose (cause that's what you're doing). It may take a bit of force initially but you should be able to rock it free.

[Datsun AshLee]

It was running but sat for about a year, just tried turning it with a socket and breaker

[spl310]

Is the transmission in neutral?

[theunz]

So, if I understand right, than the engine is on a stand without the head attached? If so will it turn now? If not than I think it may be time to pull the crank and push the Pistons out the top. If any of the Pistons don't move easily than the rings are rusted to the wall. You could maybe get by with just honing, but most likely a bore job and new piston and ring kit I'll be needed. I'm getting the feeling that this mechanic thing is new to you, as it was to all of us at one time, if so than bravo for jumping in with both feet! You are most likely to require the services of a machine shop if the Pistons are stuck, so if you can't get them out than go ahead and take it in. Machine shop prices are not very high.