CM 871

[Aussie Steve]

Hi Fellas,
I have a CM871 in a Kenworth T909 that pulls road trains in Queensland Australia.
It has a number of issues that I'm seeking help with please.
The current engine is a Cummins Recon set at 600/2050, pulling three trailers on average grossing 120 - 130 metric tonnes, [265 - 285 000 lbs] in high ambient air temps 40-45 C,
[110 F]. Its is running a double overdrive 18 speed with 4.89 diff ratios trying to maintain road speeds around 90 klm/hr [55 mph] average around 75 klm/hr. Engine at 1650 rpm at 90 klm/hr. The truck also does its fair share of slow bush work where road speeds average 45 klm.
This engine has 2200hrs and 95 000klm on it, average speed 43klm/hr
About 30 000klm into its life the problems started with high water and oil temps, more so the oil temps [stop eng light]. High soot levels in the oil and engine vibration when pulling hard, the vibration below 1500 rpm is what I would call extreme.
The oil cooler has the correct element fitted, oil thermostat has been changed to 215 F unit, water thermostat is a 160 F units. These have been changed several times [ there were some issues with faulty units]
There are no issues with radiators, water pumps, charge air coolers, Horton fans etc.
The engine was demandated at 1350 hrs and 56 000klm. We performed this on a dyno and basicly put a @m*m^2 version in it, [I'm waiting for my copy of insight to arrive to confirm this].
Horsepower output is the same as before slightly more torque. Dropped 4 psi boost pressure out of engine, it has two plates installed, one at the join at the back of the block and another where the mixer tube is.
It experienced run on issues at 1750 hrs and passed the injector leak of test.
At 2000 hrs the manifold was slobbering raw fuel, we removed the exhaust manifold and found 3 & 5 injectors leaking. they were replaced.
Currently the truck is back at the dealer with a slobbering manifold, [it was removed Friday],
it looks like it has done No 6 injector, the exhaust port is wet but the rear most valve is that clean it looks like brand new. They want to pull the head and I suspect it has washed the liners in at No 6 and probably 3 & 5 as well. It passed a blowby test but the engine has increased blowby in the last several weeks and you can smell the oil vapour.
I have an extensive maintenance history on the engine and I am fairly particular with the the maintenance. Also have an SOS history from new.
I am an ex Caterpillar fitter but this is my first Cummins so I'm flying a bit blind with this engine.
Sorry for the long winded post but there's a fair bit wrong with this engine and the downtime is brutal.
Any help or advise would be appreciated
Thanks

[Rawze]

You could always pull a copy of the tuning out and have it inspected/verified if you like. Your welcome to e-mail it to me and I can have a look at it. See if it is actually M M 2 / has good numbers in it, see if it is set to something decent.

You said you raised the torque settings. The harder you work something, the shorter its lifespan will be.

As far as higher temps goes, is it something recent?, or since you de-mandated it?

Does it still have the VG turbo on it? - or has it been replaced,.. if so, what turbo?

What is your boost and pyro gauges reading under heavy loads?

A de-mandated engine should not be getting high soot levels in the oil.

[AussieISX]

Is it fitted with a fuel pro primary fuel/water separator?

[Aussie Steve]

Hi
I will pull a copy of the tune at the first chance I get Rawze.
The torque curve is really only wider and flatter it has maybe 50 lbs increase, the horsepower is back 3hp over standard. It's running standard cummins fuelling tables with no changes to the SOI.
The heating issues forced the demandate, I was ready to burn it literally, it was that frustrating.
The VGT turbo is still fitted, we have limited turbo speed to 98K rpm.
I'm the sort of bloke that hates to modify to much. I have to be able to see a financial gain first.
Boost pressures to 240 - 250 kpa
Exhaust temps never seen them above 475 - 500 C, sender downstream of turbo, runs same exhaust temps as before demandate. Trouble is it might sit up there for extended periods when loaded.
Aussie ISX - yeh mate has the fuel pro fuel water seperator running a 50 micron fleet airs element
Tanks

[AussieISX]

I've seen a lot of fleet guard fuel pro's make air including my own . Run a clear hose from it to the ifsm and make sure it has no air in the fuel . Something is ruining your injectors and it's normally air . Air in the fuel will make it run hot . Seen it on Isx's and s60 due to the fuel pro

[Aussie Steve]

Quick update
Head is off, it has some valve recession - about 4-6 thou. The head is being replaced.
Liners are glazed especially No 6.
It's also getting 6 liner packs.
Did Cummins have problems with liners not being machined/honed properly?
Cams and top end gear looks good, I'll have a closer inspection tomorrow.
All being done under warranty.
I've been talking to the fitter doing the job about advancing the injector cam timing 1/2 a degree, so using a 4.5 wedge.
We can't get access to the dial indicators to check the SOI properly which I would much rather do. I'll try borrow something tomorrow.
Aussie ISX it doesn't behave like its starving for fuel but I will certainly check for air bubbles, probably won't hurt to change a few fuel hoses while I'm at it.
Thanks

[AussieISX]

It won't be starving for fuel. It will run hot and have a vibration and wreck injectors . I wouldn't advance the cam . Do it in the ecm , seen lots of blokes grab a piston advancing timing that way . The label on the wedge is not actual degrees advanced.

[Waterloo]

Unilever warned me of the same in regards to changing the wedges when doing the in frame on my 871, stick with the factory wedges... Let the computer do it. AussieISX is spot on.

[Rawze]

As far as the injection timing goes, you say you are using a factory map. --> The EGR gas itself was used for burn length control in that engine. You removed the gas flow, so now the engine is really touchy at its higher torque/output settings. The CM871 is not nearly as bad as the newer CM2250's and even worse, the CM2350's, but it is especially important to know that there are no factory maps designed to run higher torque output by the engine maker when there is no more EGR gas. You need all new custom injection timing, fueling, and other maps to keep everything safe under full non-egr control. Oil and coolant temps being higher than normal can be a heat transfer issue, but also can be from a bad fuel-air mix, or from cylinder temps being too high (too far advanced timing or too short of a burn length). That all goes back to programming most of the time. - Just some things to think about.

Personally, if I was faced with operating my engine at 80+% constant engine load capacity like you guys do down under, I would have disabled the EGR valve with it in a permanent open state, but used plates that had holes through them to allow for a limited/small amount of gas flow. At least some limited EGR flow will help a lot with keeping cylinder temps down and increasing burn length. This would definitely increase the life of the injectors, head, pistons, liners, etc. under such constant abuse and allow for better control of EGT's.

The whole combustion chamber and injection process was designed around that gas, and sure, most cases you can do away with it completely if you do the right things and re-program one carefully. Problem is that it starts to become a trade-off when the engine is going to be used at its upper limits under long term use. Sure the whole EGR valve and system sucks, it is a POS design from the factory, but it can also be used to maintain engine longevity under certain conditions high use too. I have seen it done before with great success on construction equipment that required a constant 90-100% torque output for extended periods of time. - Just something else to think about as an alternative of you can't get that thing under proper control.

Just some rambling thoughts on it while having my morning tea. Nothing too serious.

In any event, at 1650 rpm and high torque output, with no EGR gas any more, I wouls tend to think that your final injection timing should be around 5 degrees or so BTDC. Much more than about 6 or 7 degrees and it is in the danger zone for long term high output use. - I hear that AussieISX has done a lot of toying with this with engines that run in those conditions over there, we don't see engines being used the way you guys use them here in the states.


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250 kpa (36-psi) max on boost is ok and 500 C (930-F) on EGT's is ok too. Does not sound like you have it in any kind of immediate danger zones by those numbers, but you never know. Keeping oxygen levels a bit on the shy side like that is safer for the engines longevity.




My first thought is that something is getting the injectors too.

Just make sure there are no restrictions and everything has really good air and exhaust flow. Hopefully your exhaust is 100% open, cans are 100% hollow (or you have straight piped it). Any kind of exhaust restriction will get the injectors. Make sure you have really really good exhaust flow and that there are no obstructions of remnants of the old DPF system that can trap. reflect, or absorb heat.

Also, like AussieISX has said. Any kind of air in the fuel system will destroy them fast / cause overheating and other problems too.

Seems to be the first priority.

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These are just my own thoughts on it,.. I don't use a truck in the ways you guys over there do. After-all, I am full of S#it.