As mentioned above, you can take a few cylinders off and get a look at the internals. There?s no guarantee though that after some use, you won?t encounter a problem that wasn?t immediately apparent. Therefore, I?d suggest doing your homework on the motor, but even then, only buying it for a price where if the motor needs work after purchase, you?re not going to be left in a worse situation than if you would have bought a known good motor.