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View Full Version : Any diesel techs here?----Saltmine?



Guido
05-21-2010, 10:51 PM
The further I dig into a Cummins 24V, 5.9 diesel motor, as found in a '06 Dodge Megacab, the dirtier/blacker my hands are becoming.

1---What the devil does a 'washed down cylinder' look like????? I have a good idea of why, but what is the appearance???? And, if no physical damage to the piston is evident, does the piston get replaced anyway????

2---No. 4 piston has a very, very coarse appearance. It appears that oil or oil and fuel has flooded the cylinder, heated and boiled off, leaving the dished dome covered/coated with a hard, black/clean/dry, coarse surface. Will try to wire wheel it off to see if the piston looks otherwise normal.

3---No. 1 cylinder has piston which is clean, bright, shiney, smooth and appears as new. Five very light scorch areas on the dished dome indicate where the five orifices in the injector nozzle were impingeing their fire. Not melting, but as someone said: Boyhowdy, that there was a HOT hole.

4---Other 4 pistons have no carbon buildup, just wet with jet black, oily soot?

Troubles began since no particular person is 'assigned' to drive/maintain the vehicle, to haul materials and crew to locations around L.A. I am hearing stories third and fourth hand regarding the truck's problems with non jiving.

Strongly suspicious that the truck had a few gallons of gasoline added to the diesel tank, but no one is stepping up.

All help appreciated.

G

Bguns
05-21-2010, 11:19 PM
The front and rear cylinders tend to run hotter.

Washed down should have some type of scuff marks/ring land damage.

Had a friend lose a #1 in his 24 valve... Was towing a heavy gooseneck up a STEEP loose gravel trail.

Unknown to him, there was a small radiator leak. At that steep engine angle, the air bubble in coolant sytem at front of engine, allowed piston to get too hot and scuff up bore.

Hot day of course. He drove it to California (after a can of stop leak) with some blowby. Then a quick trip to Arizona (hotter) made blowby problem too bad to continue...

He pulled engine, had engine sleeved, new pistons. and is back in business.

The pistons are fitted tight on the newest 24 valves for emissions.

Machine shop fitted new pistons a bit looser. and no problems so far.

They do not seem to tolerate low coolant at all....

#4 on your engine might have a bad injector... dribbler or such.

Have all injectors checked...

saltmine
05-21-2010, 11:38 PM
A "washed down" cylinder just means there was an abundance of fuel pouring into the cylinder, and it washed all of the lubrication off the cylinder wall and piston. If it runs long enough, the piston will exhibit a lot of wear and scratches following the direction of the piston's motion. With the advent of electronic injector controls, a short circuit usually means the injector pops open and stays open. It's a very noticeable problem, power just goes into the toilet, and you get tons of black smoke. When the fire goes out, on that cylinder, you get raw fuel running out the exhaust pipe.

There's a U-Tube video on the "net" some guy filmed with a cell phone camera, at a Ford dealer. His 6.0 Powerstroke had a couple of injectors shorted out under his valve cover, and the result was a six foot flame belching out his tailpipe...The sound on the video didn't do justice to the horrible noises that Powerstroke was making...

Yeah, gasoline only helps a diesel when the ambient temperatures get real low. Gasoline helps a diesel start. But don't use too much.

Trying to burn gasoline, in a diesel is dangerous, and not very good for the engine. When I worked at a dealership, about once a week we had a diesel towed in with five or six gallons of gasoline in the fuel tank. Usually, they would pump the gas, pay for it, jump back in the truck and take off. As soon as the gasoline hit the injectors, it would start running horrible, then it would quit. Restarting was out of the question, you could crank the batteries dead, and it wouldn't fire. Provided the customer didn't run it too long, or try to pull a load with it, a tank of fresh #2 diesel would usually put the truck back on the road.

I'm guessing you have the head off. I would have done a compression test before pulling the head, myself. Is the head gasket intact? 24 valve Cummins have a nasty tendency to blow head gaskets in a situation like this.

I suppose at this stage, carefully measuring everything is next. If the rings show any sign of excess heating, toss 'em. If the pistons and bores are "in spec" you can probably get by with a glaze breaking and a ring job.
You might also want to pull an oil sample for analysis, to determine if there's any bearing damage.

These engines are built like a tank, but deliberate abuse can take on down in short order.

Willy
05-22-2010, 12:40 PM
As with any engine gas or diesel, check for abnormal wear patterns, heat damage, and dimensional variations from factory specs. If this means pulling the pistons, now is the time to do it.

A little gas never hurt a diesel engine unless it was run long and hard on the bad mix. What it does do a lot of damage to is the fuel injection system. Modern common rail systems operate at extremely high pressures, 25-33,000 lbs. is not uncommon. The lubricating qualities of the fuel are greatly compromised if the fuel has been diluted with gasoline. So I would definitely give the entire fuel system a thorough going over, especially the high pressure side of the system.

With the conditions you encountered you should have DTC's (diagnostic trouble codes) coming out of your ying yang. Surely they would give you an indication as to what happened. For instance, fuel dilution often sets off a low pressure code from the fuel system. This is just an example though as I'm sure if you know what to look for, the evidence will be there.

Also at this time it may be in your best interest to seek out a knowledgeable Cummins mechanic to have a good look at your situation, even if you have to pay this guy a $100 an hour to come over and have a good look, it will be money well spent, unless you want to repeat this scenario over again. Of course if this is operator neglect or abuse now is also the time to address that situation. Unless you have really deep pockets it doesn't matter what you buy them it will not last!

Edited for grammar.

Guido
05-22-2010, 01:46 PM
Saltmine------------We machined an adapter to replace each injector, and ran cylinder leakdown pressure tests. All tested 90-95% comparative quality, but it took three applications to get No. 4 to test good. For this one reason we pulled the cylinder head, and yes you're correct saying the engine is built like a tank, as in HEAVY.

For the rest of the story--------The No. 1 piston had slight indications of contacting the intakes plus both valves showed contact marks. Removed the four valves and found both intakes to be bent. How the cylinder tested good, leakdown wise, I have no clue. Upon removing the valve cover for injector R-R, both crossheads for the intake valves on No's. 1 and 2 were found disconnected. Plus, both pushrods for No. 1 were bent, so, ran the leakdown tests, expecting No. 1 to fail.

Replaced the two bent pushrods, but rod for No. 1 intake was 0.3 inches short, pointing to a failed cam follower. Dropped the pan and found parts and pieces plus a small chip off the bottom of No. 1 piston. Removed cam and found very slight scratching on No. 1 intake lobe, plus the flat face of the tappet, which measures 0.3 inches in thickness. Surprise?

Biggest question now is why do three cylinder walls have vertical 'curtains' about an inch wide, which appear a darker color than the rest of the cylinder walls. Otherwise, all cylinders are unmarked by anything that can be felt, no vertical scratches, no ringridge, just crosshatching and smooth.

Planning to pull the pistons to have a looksee for broken rings and damage. Will likely go back with new pistons/rings and cylinder honeing, plus a valve job.

Thanks for reading, send money and a forklift. But, still wondering what has caused the vertical discolorations on the three cylinders.

--G

Bguns
05-22-2010, 02:18 PM
Are the curtains in same position???

If so, it might be a spot where pistons transfer heat to cylinder wall better/worse than other spots. Wrist pin area for example.

Broken/bent pushrods/valves.... hmmm maybe overspeeding. Any downhill driving ??? doubt govenor would fuel an overspeed, but gravity could do it easily...

Man trans or auto???

Be sure oiler holes in rods are clear, easily plugged.

Willy
05-22-2010, 02:19 PM
Biggest question now is why do three cylinder walls have vertical 'curtains' about an inch wide, which appear a darker color than the rest of the cylinder walls. Otherwise, all cylinders are unmarked by anything that can be felt, no vertical scratches, no ringridge, just crosshatching and smooth.


Exactly where in the cylinder bore are these discolorations, are they all the same? Broken rings, excessive heat, cylinder distortion, piston failure are all possible causes. Once the pistons are out and both the cylinders and pistons are carefully checked for dimensional irregularities and or ring condition, you will have a better idea as to what caused the discolorations. But they are usually associated with burning gases blowing by the piston, or at least an incomplete ring seal.
Over reving is definitely a part of the overall picture though.
Can you post a clear set of pictures, as this would greatly enhance everybody's ability to give a more informed diagnosis?

hawgwrench
05-23-2010, 10:54 AM
Do you have any ideas as to the mileage/hours of use? From what I've seen Saltmine is spot on about these,they're damn near bulletproof.On the other hand,I've known some folks that could bust an anvil too,nothing tolerates abuse long.Do you have any reason to think it was run hot? I went thru a small Yanmar that had very similiar symptoms and wear patterns,and I know for a fact that it was overheated...but,its no cummins either.