I paid for a 4.0 engine at a junkyard. They later took it out of the car, tested it, and determined that it was seized. For now, they are looking into testing another of the same engine, but I am worried that might be seized too. What can cause an engine to seize? Does this happen if the engine has been sitting for awhile? Is it possible to repair? I will replace the rotating assembly from my old 4.6 engine with a bad block and head into a 4.0 engine. Will I be able to do this and get a working motor if I use the block and heads from the seized motor and replace bearings? What would be a reasonable price to pay for a seized engine? For context, I would pay $1300 if it was fully working.

 

There are several things that could cause it to seize. Good on them for testing it and not selling you a piece of junk. If it sat a very long time in a moist climate it could seize. Overheating it could also cause seizure. Yes it could still be rebuilt, but chances are high that the cylinder walls are badly scored and would need boring or resleeving. Either would add machine shop costs to your project.

 

One that has been sitting - rings can rust to the cylinder walls. Running, the bearings spin due to too much wear/clearance and then get stacked with no clearance and seize.