Cummins 855 failure

[multis6]

I’ve been working on a stationary pump engine that has been giving us problems for 5 years. It is a 1978 Cummins NT855 F1 for fire pumps. The engines it has ~ 2K hours on it, most of that time is from exercising 30 min per week pumping at the given rate of the system.
The problem we are having is that the # 5 piston is over heating with in the cylinder causing scuffing on the cylinder wall and or the crown is being melted to the point of seizing the engine. The cooling system seems to be drawing off the heat of the engine in general, the temp. gage (tested) is running in the range of 180 degrees This engine has been rebuilt now for the 4th time. New cylinder kit, (piston, rings, liner) new main bearings and the rod bearings through out.
Each time we get about 200 hrs on it before failure. The engine has been rebuilt by Cummins trained personnel from 2 different companies, and no one can give us a definitive reason for the cause of the failures.

Can any one try to shed some light on what the causes might be?

 

[bcs5274]

is the liner cavitated thru so that coolant enters the cylinder?

also what did the injectors test show? or did you replace/exchange all of them.

 

[multis6]

No in each case the cavitations were noticeable but not deep enough to penetrate the liner.

In regards to the injectors, the last break down they were sent out by the firm that was called in to do the work on engine and it was reported back to us that the injectors were fine. This time I told them to change them all.

It looked to me on the posted photo, that the spray pattern was directed to one side and it moved the soften metal to that side. It is the only thing I can think of that would make the mound of material.

 

[ivymike]

I was originally going to say "definitely injector torching" when I saw the photo, but after looking at the pic more I convinced myself it was foreign object damage. Looks a bit like you dropped a valve & it printed sideways in the piston before shaking loose and getting "digested".

 

[ivymike]

looking at it again (and since you haven't mentioned FOD), I will go back to "injector torching" as my explanation - perhaps the injector tip cracked between 2 orifices?

 

[multis6]

Injector torching due to a cracked tip sounds like a good call on this piston. There was a case on one of these where some of the piston material was imprinted with head as it came up on the return stroke. No serious damage..

Thanks every on for your insightful input. After 100 hours of run time I plan to pull the head an see what condition the parts are in. It may be the case of a slowly developing problem or a case of quick failure at approximately 200 hours each time.

Run time will tell……………..