Compression 1973 4000SU diesel: Cylinder 1 = 380 psi; Cylinder 2 = 360 psi; Cylinder 3 = 360 psi. All measurements take when engine was cold. Engine had a vibration at 1800rpm. We took it apart and found nothing wrong. Now trying to figure out how to rebuild. Option 1 (minor overhaul) = hone, rings, bearing and rework head. Option 2 (major overhaul) = sleeve engine, pistons, rings, bearing and rework head. Option 3 = Reassembly engine? This little tractor started fine and power was o.k. Having the advantage of hind sight. Should have started with the injector pump and injectors. What do you think? Thanks.