john, one thing is for sure and that is that every one has a differing opinion on what an overhaul consists of. if you plan on keeping this thing for any amount of time you should plan on doing it right. as bad a reputation the n6 engine has the risk can be minimized. one thing that is more important than people realize is the machine work. i have seen more bad machine work thatn good and know it is hard to find an experienced and knowledgable big engine machine shop. the block on that 670 will almost for certain need work. the main bore will more than likely need align bored and at the least align honed. the machine shop should also check for liner protrusion and lower packing condition. they can correct either problem. the crank should be measured and magnifluxed. if it passes the muster and nneds grinding it is even more important to have good work. very few shops have the equipment to grind big shafts correctly. the radius is critical to life of the engine. leslie had mentioned that the rods should be resized and it is for sure important that the bushings are bored. the cylinder head needs to be done completely. just because some one has a valve grinder in the back does not make them qualified. it is cheap insuance to replace all exhaust valves and any other parts the machine shop questions. a couple parts over looked at most overhauls is the cam, lifters and rockers. the lifters must have a convex profile to work properly. both the lifters and cam can be reground to be of new specs but those places are hard to find. the rockers are seldom dissassmbled but can cause lots of problems. most show signs of gauling to rocker shaft. if the shaft shows signs of wear, replace it. any rockers that are worn or gaulded at bore, replace also. any rockers that just show wear at tip can be ground. be certain to replace the crank dampener, i use the shop floor test, if i throw it up and it hits the floor i replace it, ha, ha. it is hard to look at it and tell if it is good or bad, all experienced mechanics and service manuals tell you to replace it. one other thing i do and have had exceptional results from is balancing 670's. the machine shop will balance pistons and rods. they will spin balance the crank, flywheel and front pulleys. that should take care of the trip to machine shop. i next box up pump and injectors and send them to good pump station. when i do overhauls this is not optional, it is a must. leslie also mentioned the cooling system, while the engine is out it is all but too easy to remove radiator and have it repaired and at the least cleaned. every thing on the left on the engine needs to come apart and be repaired, replaced and at least resealed; water pump, oil pump, innercooler, etc. most likely the pulleys are worn, if they are replace them; if the engine is fresh and strong you will need good performance here. ......didnt mean to be so long winded but there are lots of important points to hit...............good luck vstk
