Cummins 855 failure
Cummins 855 failure
(OP)
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?
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?





RE: Cummins 855 failure
RE: Cummins 855 failure
RE: Cummins 855 failure
RE: Cummins 855 failure
The oil gallery on the right side where the oil nozzles are, was made with no feed lines open, there is no oil spray from nozzles cooling the pistons from below. Due to the fact that the engine was for fire pump application it was built to run in extreme conditions and no oil is used to cool the skirts
We have a total of 3 engines side by side built the same way, each having the same configuration and running fine.
RE: Cummins 855 failure
For what injectors cost we are having new installed this time around.
Potteryshard Another good point. The cam lobs have not been checked at this time. I'll pull a cover and check this out.
RE: Cummins 855 failure
RE: Cummins 855 failure
I DID have a 1978 Cummins 855 once upon a time in an automotive application and I DID have some pistons that looked exactly like that but it was because the driver had monkeyed around with the injector pump and over-fueled it so much that it literally melted itself. Only a couple of the pistons looked like that. But you should have heard the stories up and down the road about how well it pulled (it was distinctively marked so it was easy to determine that it was my truck being bragged on). Has anyone monkeyed around with the pump on this one and "turned it up?"
Is this a turbo'd engine? And if so, is it a 300HP version or a 350HP? Someone may have tried to make a 300HP run like a 350 by turning up the pump. The timing and advance is different between the two and you can't get from one to the other by just 'turning up' the pump.
rmw
RE: Cummins 855 failure
The root cause is often overfuelling or late timing but can be lack of lubrication or lack of cooling (oil squirter blockage) etc.
Engineering is the art of creating things you need, from things you can get.
RE: Cummins 855 failure
Dicer, early on it comes back to me that the first person to work on the engine did go through and adjust the timing with the shims under the cover of the cam followers and a gage on top. Now weather these were set correctly is a good question. The standard NT855 is so common that the parts guys often don't see the F1 at the end of the model number. This makes a bit of a different build. That's something to check.
I have pulled the follower cover on 5&6 and find every thing to be in good shape. The cam is not worn, the rollers are tight and in good working order.
RMW The engine runs smooth right up to the point of failure. At that time I have heard it start to drop in RPM slightly and have a bit of a subtle clatter to it, not real bad but noticeable. I am assuming that the piston is starting to swell and tighten up at that time.
The fuel pump has been pulled and rebuilt, actually adding a few leeks that were not there in the first place. These engines are turbocharged and rated for 255 HP @ 1750 RPM and actually run at 1600 RPM once the oil pressure gets up to 65-70 PSI.
Some times I wonder if the constant speed is a detriment to them.
RE: Cummins 855 failure
That does not rule out localized overheating, perhaps from casting sand or flaws in the water jacket.
Careful mapping of the block with an infrared thermometer might reveal an anomaly around #5.
Mike Halloran
Pembroke Pines, FL, USA
RE: Cummins 855 failure
RE: Cummins 855 failure
Thanks for the reminder.
RE: Cummins 855 failure
Steve
RE: Cummins 855 failure
I used to know my way around that engine pretty good, but it has been over 20 years since I have been the proud owner of a "come apart." When mine came apart, other than the one time I mentioned due to the driver turning up the pump, it was usually due to a cooling system failure, usually that little chicken neck shaped piece of hose on the side opposite the fuel pump. I can't remember what it went to, just that when it failed - and it was famous in the industry for failing, in those days it was a ~$15-20,000 ding. And that was when that much money was a big chunk of an engineer's annual salary. Bought several new "come apart's" over the years. Wouldn't have one today.
rmw
RE: Cummins 855 failure
I see how some blockage in the engine coolant ports could be problematic in drawing off the heat causing the build up of heat in one cylinder. I'll need to look deeper.
Thanks for the continued input.
RE: Cummins 855 failure
As the concentration of glycol goes up, the viscosity and density of the fluid changes, and with respect to pumping it(relates to flow through the engine) and soaking up heat with it, the higher the concentration goes, the worse the stuff gets with respect to carrying off engine heat.
What kind of ambient conditions is this engine having to exist in?
I just ran a case where the glycol solution at a certain low ambient temperature became so viscous at the concentration that the case was based on that it could not flow into the engine fast enough to blend with the warmer fluid in the engine with the pumps present.
rmw
RE: Cummins 855 failure
In the past I have gotten the old green coolant from our motor pool. It was a premixed 50/50 (tested to confirm). Now on this motor I've been told that the " yellowish universal coolant" is all that is available, so at this time that is what is going in. It will be mixed on site to 50/50 blend. Personally I would like to stick to the green, but we'll give the new stuff a try.
The engines are in a clean heated block building with fresh air vents measuring 48 in X 120 in,. the louvers open when the engines start and or when the ambient gets in the 90s during the summer. The engines have block heaters (oil & coolant non circulated at rest) on them keeping them at about 120 F for a quick start with out warm up.
RE: Cummins 855 failure
ON the other hand, if you got the "Green Goo", that stuff was thick (different than cold viscous EG or PG) and nasty and would plug up cooling ports in the engine.
Another thing that the maintenance of the chemical make up of the coolant accomplished was to minimize electrosys of the cylinder liners. Now that is a problem that Cummins were famous for in the day.
rmw
RE: Cummins 855 failure
The green goo has not been a problem in this case. We do use a coolant filter with the DCS additive and it seems to work quite well keeping deposits from building up. That is a good point to watch for on further inspections.
I found some photos of the inside of the block and the piston on the engine we have been working on but at a different episode.
Dose any body see something we've over looked?
I have seen pitting on the sidewalls of the liners even after just 2 years, it was most noticeable where the coolant port in the block emptied into the liner cavity. Small pitting was there in a line on each of the liners that have been removed.
RE: Cummins 855 failure
also what did the injectors test show? or did you replace/exchange all of them.
RE: Cummins 855 failure
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.
RE: Cummins 855 failure
RE: Cummins 855 failure
RE: Cummins 855 failure
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.................