Combines Overhaul N6 Engine

You can get the kit at your dealer, no problem, should be around $1k give take a couple $100.00 Check the kit to see if it has the thrust bearing in it,, We have found thet some time they do and sometimes they don't, and Im not sure if is suppose to or not. There is a new style valve cover hold down part number 74036977. If yours is prone to leak at the valve cover these seem to work pretty good.. Be sure to have thr rods reconditioned with new bushing.... the bushings should be bored not honed to fit.. Honning them will cause premature failure. A pump recalibration is always good idea at this time, but do not neglect the cooling system if you do any fuel work....Don't forget the injectors too......

The rod bolts should have a bulletin with them about torque settings, be sure to use that number and not what is in the service manuals. Also, it seems like the rods needed turned 180 degrees on the crank for updated rod bearing on my 7050. I wish I could remember better, but it might be worth asking your dealer about. Best of luck, Mike

Get some good gasket sealant for the jigsaw puzzle oil pan gasket. Your dealer should be able to suggest a good quality sealant. That is an engineered leak just waiting to happen.I'm sure you won't want to pull the engine out again just to reseal the pan because the Allis engineers couldn't figure out how to get a one piece gasket in the engine kit box.Good luck.dslman

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

Good advice. Dont forget the oil cooler oil filter assembly. Have had annoying leaks out of them did'nt want to takle it but nothing to it . A few o.rings here and there a couple of gaskets and all done. Don't forget o.rings on either end of pipe that runs up to front of motor! Peng.

The N6 used two different engines! The first group was the 670HI or better known as the 7080 and blowing up engine. The second group was the 670I or better known as the 8000 or R series engine. When you go to get parts their is a difference. The easiest way to tell them apart is the injector pump. The 670HI uses a Roosamaster pump and AC nozzles and the 670I uses the American Bosch(Ambac)pump and nozzles. About 1982 is where they made the change in the system and didn't tell alot of people. I thought I had the N6 engine and all were bad and the R6 had the good engine and slowed down 200 rpm and found in the service manual that both were used in the N6. And according to my dealer that did my UnderHaul at 3100 hrs(rod and Bearings)their is a difference between the older HI and the newer I engines besides the RPM's , Crankshaft and Injection system. Make sure which you have!

I worked at an AC dealership for years and overhauled many AC engines DON'T USE A REGROUND CRANK every one I ever saw used blew up.

this just goes back to the comment i made that there are very few machine shops that know how to and have the right equipment to do things right. i have used well over a hundred.........probably twice that........ground, welded, and combo there of. never......not ever has one failed. my mchine shop knows how to do it right.this has been in A_C, deere, cat, cummins, and many other brands. there are not many shafts made that cant be repaired short of busted into 2 pieces. i wont dissagree that all of your shafts broke that just goes tomprove the point that machine shop selection is very important...........Ignorance on the part of mechanics not knowing right from wrong ussually puts the blame on the wrong thing.

I guess you are lucky. The last one we tried was done by a shop was supposed to be one of the best. Shot peened radius reground the whole works, lasted about 500 hrs. When I tore it down it broke right where the radius meets the crank. No more, I will use new ones cheaper in the long run.