rsync to synchronize by time or size
 

I am trying to use rsync to synchronize by time or size, like this:

SERVER A and SERVER B.

Files modified in server A should be modified in SERVER B only one dir.
In another dir files modified or created in SERVER B should be created or update in server A. All process over SSH

I am trying with something like this but do not work.
rsync -av --rsh="ssh -l user" user@remote-machine::remote_dir/dir /local_dir/dir

It's possible?