Carbon build up on cylinder wall.

[TugboatEng]

I'm just looking for some quick input. I operate a fleet of Caterpillar 3500 series engines and have cylinder heads off of one engine for other reasons but noticed a build up of carbon on the cylinder wall thick enough the piston crown is hitting it. It is only in one portion of the cylinder and there are no other unusual deposits elsewhere. Is there a chance the injector is not atomizing properly out one port and fuel is hitting the cylinder wall? The wet appearance is because I hosed everything down with wd40 to prevent corrosion over night.

 

[TugboatEng]

No other major deposits.

 

[tbuelna]

Carbon deposits on the upper circumference of the cylinder liner are a common issue with CIDI diesels where the upper compression ring is located well below the piston deck. The upper ring does not travel far enough up the cylinder liner to scrape away the deposits. They are both oil and fuel deposits. The fuel deposits on the cylinder wall are the result of incomplete combustion, typically from quenching of the fuel injection spray. The lube oil deposits are the result of excessive temperatures in the oil film at the upper edge of the cylinder liner surface. This upper area of the cylinder liner surface is difficult to cool properly due to the structural arrangement of the liner flange and cylinder block deck. Some large 2T diesel engines use a wiper ring at the upper cylinder liner edge to prevent accumulation of these deposits.

If a fuel injection spray jet was impinging on the cylinder wall you would probably see thermal distress at the location.

 

[catserveng]

Heavy deposits in those areas of the 3500 diesel engines are usually due to extended run times at lower loads, typically less than 40% of rated. Do you have CAT ET? If so can you take a look at the histogram and see what the average load factor is?

MikeL.

 

[TugboatEng]

Company does not feel I need Cat ET. They ran EMDs and D399s for years without computers. Anyways these engines are in ship assist tugs. They average out to about a 25% load during their life with with about 15% spent above half power. Some engines a B rated and some make almost double the power with a C rating in the HD block. I have never seen any significant carbon build up in those engines. This is our first engine with the second generation piston a one piece iron piston. We noticed substantially more blowby after the overhaul to the point we added a Parker closed ventilation system plumbed to the air cleaner housings to reduce oil mist in the engine room.

 

[TugboatEng]

These are from the second cylinder. The light colored spots in the cross hatch are unusual too.

 

[dicer]

Personally I think the cross hatch is excessive, way too course, and that is likely passing oil. How is the oil consumption?

 

[TugboatEng]

These are factory liners with 8500 hours on them. Oil consumption seems reasonable, about a gallon in 24 hours but it's hard to get good numbers from the crew.

 

[catserveng]

The cross hatch pattern appears normal for this family of engines. I agree the "spots" are abnormal, in both the top and second ring turn around areas. Are they small pits? They almost look like fretting but hard to tell from the pictures. CAT had an issue with rings many years ago that resulted in a similar appearance on the "spots".

The hard black carbon deposits on these engines is typically from incompletely burned fuel. If they were due to excessive oil consumption they usually have tan to brownish colored areas in the deposits from the lube oil ash. I assume you are using a multigrade DEO?

If you had raw fuel from a bad injector hitting the cylinder wall it usually results in vertical scoring of the cylinder liner. Does the crown of the piston indicate the injector spray pattern? In a lot of these engines you can see equally spaced oval "discolorations" in the bowl of the piston, number of these are dependent on which injector you have, Eight holes is most common, but also injector tips with 7, 9 and 11 holes were made.

What does your servicing CAT dealer have to say about it? The report of excessive blowby is also a concern. I have not had any experience with the new piston. I spend most of my time these days around the gas engine products when I do work around the engines. I would suggest you get your local dealer to put in a DSN ticket on it and see if CAT has any input. You can also try the CAT forums here,

http://forums.cat.com/

and see if any one else is having similar issues. It would be helpful if you provide your engine serial number and the piston part number for the best possible answers.

Hope that helps, MikeL.

 

[TugboatEng]

Just put the engine back together tonight. My take away is that the deposits are not caused by fuel impingement. Anyways the heads came off because of coolant leaks caused by rotten spacer plates. But we have been having some smoke issues lately. I saw tI he carbon deposits and found them a bit unusual. We rarely pull heads and bring in outside contractors at overhauls so I don't always get a close look at things.

For more info, the engines run Chevron Delo 400 MG 15w40 oil. They are serial number 4TN 3512 engines. They were recently converted to epa tier 2 which involved a firing order change, new cams, and a switch from Abb turbos to Garrett. I'm not happy with any of the Garrett turbos I have in service so I am not ruling them out as a problem either.

And the white spots. They are not pits. Fretting seems the better way to describe them. If I took a sharpened pick and dragged it across the spot it would not snag.

Oddly the turbo on this bank had much oil residue in the outlet ducting while the other had a light coating of soot. I expect at 350F discharge temps most oil residue would burn. I have not had a chance to look into why one duct was oily and the other not.

 

[tbuelna]

Are you sure the deposits are carbon and not smeared metal? It's a bit hard to tell from the photos. The presence of cylinder wall scuffing above and below the compression ring travel is unusual. It might indicate overheating of the piston body. The piston is oil-cooled, and if there is insufficient cooling oil flow the piston body will experience excessive thermal growth and possibly seize up to the cylinder bore. The scuffing seems to be in the direction of the piston skirt thrust contacts.

 

[gruntguru]

The white marks appear to coincide with the location of the top and second piston ring at TDC. Looks like a deposit resulting fron breakdown of the lube film when the rings undergo a load reversal or step change.

je suis charlie

 

[EHudson]

That looks like scuffing to me. Scuffing is a welding of piston or ring material to the cylinder wall which is subsequently pulled out by further motion of the piston.

 

[gruntguru]

OP says the white spots are not pits.

je suis charlie