We've been putting a 115 hp Evinrude outboard back
together for a little over a year now. It took some time,
but we finally got all the pistons turning easily and
smoothly. We mounted the block back and attached
it to the lower unit, and then put the heads on. I don't
remember when the last time was we tried to move
the pistons, but at some point we did something wrong.
There's something solid stopping the system somewhere
and it only lets us turn the flywheel about 1/4 turn or less
in both directions before something clonks into something
else and stops its travel. Could we have put a head on
wrong so it's catching a piston, or is it likely to be something
in the lower unit like a spline lined up wrong, or what?

Thanks for any help!