Help just finished rebuilding a 3.9 the pistons went in tight it will only crank one revolution with the starter then stop plugs out belt off. I got marvins soaking in cylinders right now hoping to get more lubrication. Is there anything else I can do other then breaking the engine down?

 

have you tried turning it over by hand cranking to rotate it through the full cycle a few times? Sounds like something did not stay in place or is not seated correctly.

 

Yeah I can get crank one full revolution but it stops. Its to tight to turn by hand. The reason its so tight is four of the pistons are really tight in the cylinders.

 

Are you using gapped or gapless rings? If gapped, did you set the ring gap on them?

What bore is the cylinder, what size are the pistons?

It sounds like the rings aren't gapped properly, causing the rings to seize up against the wall. However, I'm not a professional motor builder (having done two lawnmowers and one 302W over my 58 years ... ) so take this with a grain of salt.

RwP