G1625S

Well, my work truck puked a cylinder liner on wednesday Teardown produced a slightly upset piston



Since I've got my spare 12v on the bench, I thought I'd line up some pieces side-by-side. 855 aint no joke! I think the wrist pin weighs 10lbs I love huge engine stuff



What I did find interesting is the rod journal is not all that much bigger in the class 8 engine...prolly why the 5.9 bottom end is good for such absurd amounts of power

C Schomer

The B's and C's were developed for 3rd world multifuel tractor engines and Cummins didn't know what kind of lousy fuel would be used so they built the bottom end to withstand the predetination. Craig

G1625S

Good point, never gave that a thought! I love both my Cummins engines...despite the fact that they're both down for the count presently

bigwheels94

Yup. too bad you don't have a duramax, & a powerstroke rod assly to compare. They look like small block chevy parts.

HMX-1

Isn't that what they are anyways?




Kris

Rednecktastic

Yup, the B series are tractor motors designed by case/cummins.

Hvytrkmech

How were the thrust washer/bearings? That piston looks like the crank may have been walking back and forth.

G1625S

I don't know....what main is the thrust on? I prolly should pull it down and look. Engine is the nt855 in my military 5-ton. Engine has about 30k miles on it. Looks spotless inside, but, being a 1970 model has likely been sitting forever and a day. I can't really afford to do a complete in-frame, so what should I look close at while I'm right there?
Thanks!

Hvytrkmech

Thrust washers are on # 7 journal. You can see them very clearly, try prying the flywheel back and forth, you should have nearly no play. If you are only going to do the one hole then at least throw a bearing roll at it. Rods and mains (kit) is only a couple hundred bucks, you can also get the thrust washer separate for around 50 bucks.

Unless there is something really special about the military engine, you can throw an overhaul kit at it for right around 4 grand. All new liners pistons bearings and gaskets.


Good luck.

G1625S

Thanks for the advise, Tim Unfortunately, an in-frame is not in the budget on this old girl. I do believe I will roll bearings into it though. Is the thrust part of the main bearing like the b series? Crank doesn't have to come out, I hope. Other than fuel and oil filters and a special oil pan to clear the monster front axle, I've found it to be pretty much identical to a standard nt855. Thanks again!

C Schomer

I wonder if that injector is squirting too much. The NT doesn't have oil cooled pistons and are more likely to score the cylinders if run too hard when cold. Actually, I thought they were all NTC's by 70. It also wasn't unusual for a cooling nozzle to break off on the NTC's and score a hole. What hp is it? Some NT's used the NTC block and they can be turned into an NTC. I did that with the NT I had. Craig

G1625S

Horsepower is only 250. The thing is absolutely gutless. It does however start well and run very smooth. No smoke ever except a little cold weather blue puff. Injectors are brand new with about 200 miles on them. Here's a shot of one of the thrust washers. Lousy pic, I know. They've got some scuffing, but not too bad....but the crank did walk abit with the prybar, so I'm gonna replace them.