Injector Spray Pattern - LMM

[kidturbo]

Marine applications are bastards for thermal shocking all engine parts. Blocks and heads too.

I thought you had run some Oval Bowls....

The main problem has to do with pressurization of the area above the fire ring. Think of a fire cracker in a paper cup and how it splits. If that area does not pressurize enough, the piston will fail under normal loads and applications. There is no margin.

That sounds reasonable, as I kinda recall the discussion on pressures vs timing BTDC and piston stress points. Unlike the stockers I've seen, this Mahle didn't crack across the top or the lip. Only a hole in the bowl, sure wasn't what I expected... Then realized there was no improved oiling, which skews all the data of similar pistons in my original LLY marine setup.

Any yes I have "two" marine engines setting here with 16:1 oval bowls and TBC ready to fire up. It's just been a on again off again build, that's finally about ready to wrap up.


Mailbu, I don't know what his oil temps were cause he wasn't monitoring them at that time. Originally there was both insufficient oil and air cooling issues, which were corrected after the first stock piston failure.

My boat never saw a 195F EOT after the last rebuild. Typically ran somewhere around 165-180F tops. Because the coolers we run are so massive and copper core, the oil temps typically didn't fluctuate very quickly. Reason this one has me stumped. The engine above saw 60+lbs of boost running compounds, then went to a medium size single and ran cooler with much less pressures. Till it popped..

 

[WolfLMM]

Here's some info to chew on. IMO the ultimate strength of the piston has to be addressed like stated above. But keeping the piston cooler helps as well. Wonder what temperature the top of the piston gets soaked to on a nice wot run (over 1 minute duration)??

Sent from my iPhone using Tapatalk

 

[Fingers]

I don't want to completely discount cooling as a factor. Specifically, shock cooling/heating. Keeping the engine/pistons cool is a good thing and should reduce the shock swing on the pistons.

However, cracking on rapid load application is an indication the the core of the piston is cool while the piston head is suddenly Hot or that on the previous shut down the head cooled down rapidly around a hot core. The stress comes from two parts of the piston material being at drastically different temps. Very hard to tell which is the case if it was indeed a thermal shock issue.

 

[kidturbo]

It's certainly a chicken or egg conundrum.. That's produced a wide spectrum of answers from what I consider very seasoned professionals. And now there's this trend emerging, which can likely be replicated, or avoided.

I have a theory based purely on speculation and little data available at this point. So here it goes.

The major difference between a truck and boat setup on "oil cooling" is efficiency. Marine coolers are about 3x larger than the OEM plate stack, plus transfer rates are way better and quicker with pure copper. Add the incoming coolant side temp is half that of a warm truck. 70-100F vs 170-220F on a typical truck that has set for 10 minutes hot.

So we have this heat soaked engine which receives relatively cool air and oil soon as it fires. Now that oil down in the pan is likely still very hot, so viscosity is high and pump pressure low. Then it hits the marine cooler which takes 200F+ pan oil and drops that to say 140'ish before returning to the block. But at hot idle oil pressure is likely in that 25-35psi range due to viscosity entering the pump. Guess what's closed by design at under 30PSI ? The squirters.

Now you jump on the throttle, engine load peaks, and piston topside jumps to 1200-1400F within a couple seconds. RPMs come up, squirters are now flowing above 35psi, and bottom side of piston starts getting hit with a 140F oil spray. There's your shock action. Credits to Sting if true

But something is still missing, hidden inside that 5-10 min heat soak period...

To those who may ask how the LLY boat setup is still alive then? It's running same cooler, filter, and pistons as LMM above that just failed. Personally I though it was due to the newer no lip Mahle piston. But now the more I think about it, that engine always maintained 35psi+ pressure at hot idle on a mechanical gauge, and has enlarged squirters. Possibly pulling heat away sooner upon startup, thus equalizing the overall piston temp before the big power blast hits. I also heavily torque limited that tune below 2400r so as not to damage the outdrive. Adding a few more seconds of cushion before temp and cylinder pressure maxed.

Who knows, it's all just speculation right now. I can only hope these oval TBC sets show promise, and longevity of coating adhesion in this environment.

:thumb:

 

[kidturbo]

And to your much appreciated research Fingers, check out this 6.0L Powerstroke piston I cracked several years back. This one might be a good example of thermal shock cracking

Engine was stock, hot tune added, heads started to lift. Typical 6 leaker downhill slide. I continued to run it till she blew off more coolant than I could afford. When we tore down to stud it, I found this nice little crack hidden under some soot on cyl #1 piston. The same hole that was obviously leaking the most coolant according to the gasket and etching on the wall.

Unlike a Duramax piston, this crack didn't take off across the top or blow thru the rings. The guy doing the stud job actually didn't notice it until I pointed it out. But the catch is, the 6.0L pistons don't have an oil passage cast under the bowl. So it's beefier than a dmax in that aspect. But still failed, from coolant hitting on decel I presume. She was certainly drinking it.. All the other pistons were fine, it's still running today.


And before I forget, as to WolfLLY point above, it's actually common to add piston oilers to very high HP marine gas engines to help cool the pistons. Those engines making over 1000hp typically all use piston oilers. So it's proven tech for long term survival in this type application.

 

[kidturbo]

Finished disassembly of the block above. When the piston failed, it was directly in line with a port on the nozzle. The aluminum above the pin looks like someone took a torch to it. Even cutting through the clip and oil ring. Amazing the amount of heat applied to such a small area when they go.

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[kidturbo]

What we did find concerning but unrelated to fueling, the disregard for replacing an oil pump and reluctor ring when this engine broke the crank.. Impressive work guys, proud to show this off for ya...

Someone took the oil pump apart and cleaned it. Then they used lock tight on the gear nut. That gear spun on the shaft as we attempted to remove it. No idea if it was spinning prior, but will for certain always pin our pumps after actually seeing this issue for first time. The kaleidoscope pattern is pretty cool additional to the bent reluctor ring. Did ya charge extra for that??

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[PureHybrid]

And they probably charged as much labor to clean it, you could have bought a pump!

 

[D1rty-max]

Finished disassembly of the block above. When the piston failed, it was directly in line with a port on the nozzle. The aluminum above the pin looks like someone took a torch to it. Even cutting through the clip and oil ring. Amazing the amount of heat applied to such a small area when they go.


Sent from my SAMSUNG-SM-G870A using Tapatalk

When my lbz went the piston looked exactly like yours I had a hole on top with deformed melted metal around the wrist pin and it melted through the rings when it blew through

 

[Fingers]

Once the piston cracks into the oil gallery, the engine oil itself burns like a super hot torch destroying the piston more. Small cracks turn into big holes fast.

 

[kidturbo]

A little air pressure doesn't hurt the process either.. It's funny how some of these just crack open, while others blow clear thru and can burn a ring and steel pin clip in half with ease.

I did a little load comparison last week towing a 10k boat through the mountains of I77 with my latest daily driver, a 2004 5.9L C.. It's got bigger turbo, unknown oversize injectors and some decent tuning. In tow haul mode I could keep the calculated loads under 70% and EGT's in the mid 12's making about 18-20lbs boost on long hills. But when I left it in 4th locked up, easily pushing 95% load, 1450's and climbing on the EGT scale at around 36lbs boost. That's about equal to pushing a 1:1 geared boat WOT to get on plane. However being this was a Cummins, I wasn't scared to leave it pegged there till the ECT hit 230F. Is that weird or what? :spit:

 

[Stingpuller]

EGT's

I think that is the problem with 6 speed trucks. I never tow in 6th and when pulling big hills don't be afraid to shift down and run a little rpm's. Just because the motor has enough power to pull a taller gear doesn't mean it should be doing it. Ken passed you just as you crossed the bridge coming into Ohio. I was heading to WV to camp and ride the SXS.

 

[JoshH]

However being this was a Cummins, I wasn't scared to leave it pegged there till the ECT hit 230F. Is that weird or what? :spit:

I think it is.

 

[kidturbo]

Sting there is certainly less stress applied on the internals by down shifting. Might sound like it's working harder all revved up, but the CTS data tells the tale. In my hill tests, the previous owners snow plowing fan shroud delete proved to be the limiting factor. She couldn't stay cool loaded, and is reason you passed me at 7:30AM. I had to pull it over in SC and sleep the previous day. That rig wasn't gonna make it home in mid 90F daytime temps, I'd bet the title on it.. lol

Josh, on a Dodge they tell me the only gauge that really matters is that bottom left on CTS shot below. There's an idiot light in the dash too, comes on at around 240F I can verify. Even fully built by Dodge lover standards, tranny is a ticking time bomb...

 

[JoshH]

I don't know where people get the idea that a Cummins is indestructible. I've rebuilt plenty of them for various reasons. The last one I did had a piston that looked about like that Duramax piston you posted. It was from a 2016 Ram 3500 cab and chassis with about 70k miles on it. The only modifications were a DPF delete and a 30 hp tow tune. Stock to stock is the engine stronger than a Duramax? Absolutely, but making them out to be flawless and trouble free isn't something I can agree with and is bordering on Cummins fanboy territory in my opinion.

 

[kidturbo]

Stepping out of a 6 L Ford after eight years, Cummings is definitely more reliable. But this s.o.b leaves oil spots all over my driveway yet never uses a drop. And the electrical system is about to drive me freaking batty...

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[NC-smokinlmm]

Haha, Windows hardly ever work and one headlight out? :roflmao:

 

[kidturbo]

One fog light, no heater control lights, odometer came on once three months ago at 298. What's worse is this bug that after driving several hours with cruise control set above 75 it goes into limp mode and down shifts. Get your attention when a 3100 Redline is turning 45...

Put the engine above back together tonight with a new piston. Here is the squirters old vs new LML. Getting an LML pump upgrade also..

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[kidturbo]

Had those injectors inspected and flow benched again [4th Time] before downgrading the tips for the new application. All's well within specs. So......

And, here is video of a pair of 5.9L Cummins on dyno running at 1000hp for extended periods before getting dropped into a certain go fast boat. All I can say, time to step it up boys..

[YOUTUBE]l9eicKvrqNg[/YOUTUBE]