Odd Colored Piston Head

[jetattblue]

Odd Colored Piston Head - Pic Added on 2nd Page

I have very little engine experience, but I am working on a couple of Kubota tractors as fun projects. One of the tractors is a Kubota BX1800 with the D722 engine. I purchased knowing that it had low compression in the 2nd cylinder.

Today, I took the head off of the engine, and this is the first time that I have ever seen the inside of any engine in person. I was struck, however, by the color of the top of the 2nd piston. Although I have not removed the pistons yet, I noticed that the top of the 2nd piston (the cylinder with the low compression) was a flat gray color - almost the color of primer. The other 2 pistons looked more like I expected; they had a black sooty/oily appearance. The difference was very apparent.

Does anyone have any thoughts on what might cause the top of the 2nd cylinder to have the flat gray appearance and not the black-ish sooty appearance of the tops of the 1st and 3rd?

Thank you.

 

[SidecarFlip]

Maybe low compression (did you check it to be sure), but sound to me like you have an injector issue, not a compression issue.

 

[ipz2222]

Lean fuel mixture, bad injector.

 

[North Idaho Wolfman]

You said it had low compression, so it's easy to say it's not firing properly.

Now did something like a bad injector cause it to wash the cylinder and ruin the compression, or did something else cause the low compression issue?

 

[jetattblue]

You said it had low compression, so it's easy to say it's not firing properly.

Now did something like a bad injector cause it to wash the cylinder and ruin the compression, or did something else cause the low compression issue?

I'm guessing it had something to do with fuel delivery - although my opinion is admittedly inexperienced. It just seems strange to me that it would be SO pale gray compared to the other cylinders. Is there some way to test the injectors with it disassembled like this? Or, can you take the injectors to be tested somewhere?

As an aside, I was taking the seller's word on the low compression. The only thing that I can say for sure is that it was very, very difficult to start. I really don't know if he measured the compression or not. Otherwise, the engine looks really clean all over.

I was planning to do a pretty serious rebuild, so I don't mind taking it down further, and removing the pistons all the way to measure them, inspect the cylinders bore and replace the rings.

What would you all suggest as my next steps?

 

[D2Cat]

Hindsight says you should have actually tested compression before removing the head. You could take the injectors to a diesel injection pump repair shop. They can test your injectors. Then you can maybe determine the hard start issue, or a part of it.

 

[SDT]

You said it had low compression, so it's easy to say it's not firing properly.

Now did something like a bad injector cause it to wash the cylinder and ruin the compression, or did something else cause the low compression issue?

Easy to understand how overly rich mixture can wash the oil film in a gasoline engine but cannot comprehend how this can occur in a diesel engine.

???

SDT

 

[thepumpguysc]

If the rings were bad & u had low/no compression, the injector would still fire fuel into the cylinder. {from the injection pump}
The fuel would then just lay there & cook.. & possibly pool-up & start to run down past the rings.
How did the engine oil look when u drained it?? Thin? Black, Smelled Burnt?
A diesel fuel injection shop that rebuilds pumps will test your injectors..
Take ALL OF THEM, not just 1.. You certainly don't want to put a bad injector in a freshly rebuilt engine..
DONT FORGET> there are TIMING SHIMS under the injection pump{thin brass} DONT LOSE THEM.. Just put them back under the pump when your ready.. I like to TIE them TO THE PUMP until I'm ready for reinstallation.
Good luck w/ your project..

 

[SDT]

I have very little engine experience, but I am working on a couple of Kubota tractors as fun projects. One of the tractors is a Kubota BX1800 with the D722 engine. I purchased knowing that it had low compression in the 2nd cylinder.

Today, I took the head off of the engine, and this is the first time that I have ever seen the inside of any engine in person. I was struck, however, by the color of the top of the 2nd piston. Although I have not removed the pistons yet, I noticed that the top of the 2nd piston (the cylinder with the low compression) was a flat gray color - almost the color of primer. The other 2 pistons looked more like I expected; they had a black sooty/oily appearance. The difference was very apparent.

Does anyone have any thoughts on what might cause the top of the 2nd cylinder to have the flat gray appearance and not the black-ish sooty appearance of the tops of the 1st and 3rd?

Thank you.

Had the engine been using coolant? Smoking?

Piston could be steam cleaned due to cracked head or failed head gasket.

SDT

 

[CobraTom]

I had a similar looking piston in a v2203 that had stuck rings and low compression on one cylinder. Because diesels are compression based there is not enough compression to ignite the fuel and the piston just gets washed every time. Take a look at the exhaust port of the cylinder in question, should be fairly clean as some unburnt fuel would have exited through it.

Typically there is only one way to test the strength of the rings at this point. If the compression rings are bad they would have destroyed the oil skirt on the piston, so you pour the same amount of varsol or another non corrosive liquid that is similarly thin in each cylinder hole and you time how long it takes to weep past the seals.

A engine with good compression it would take forever to let the liquid past, if at all. (depends on how good the cross hatch pattern is on the cylinder and how tight the rings were installed)

 

[jetattblue]

I really appreciate all of the insight, folks!

The engine was not smoking when I finally did start it, but I just moved it into the barn to work on it. In other words, I did not put it under load or run it very long at all. When I drained it, the coolant was full and had a very vibrant green color - so I am assuming that means it was new. This was purchased as a project to work on and learn from.

The failure to create enough compression to fire makes a lot of sense to me as does the fuel injector's failure to deliver fuel. The top of piston 2 just doesn't have any sign of burning on it. I'll check the exhaust port, then, depending on what I see there, break it down further as I was planning to replace the rings at a minimum.

Again, I really appreciate you all taking the time to review this and help me with it!

 

[rbargeron]

Reading your first post, I was thinking the one poston was getting steam cleaned like SDT suggests. Maybe a small crack that mostly closes on heat-up but pushes a couple drops in on cool-down? Did it tend to lose coolant level before?

 

[jetattblue]

Unfortunately, I'm not sure if it was losing coolant as I just didn't own it long enough. To chase down a crack (assuming it was not obvious to see), would I need to have it checked at a machine shop? Or, is there some way to do that at home?

 

[hagrid]

I read somewhere that the picture/word exchange rate is 1:1000.

 

[jetattblue]

Hagrid, That's a fair point. Attached is a picture of the piston tops. It's a little difficult to decipher color, but this should help. Pistons 1 and 3 are black, and you can see that they have a wet or oily appearance - which I understand to be normal. In contrast, Piston 2 has a matte gray appearance. It's very light gray, and, this pictures shows that it is much, much drier looking.

Notably, the coolant in the closest cylinder was not there until the engine moved while removing the head. In other words, it was introduced into the cylinder during the removal process. It was not there originally.

 

[jetattblue]

Here are the only other 2 pictures that I have at the moment. Again, while it's difficult to see the light gray color of Piston 2, you can clearly see that it is matte/dull on top, while the others are black and have an oily or sooty sheen to them.

 

[D2Cat]

Might take the head to an engine machine shop and have them magnaflux it. Then you'll have more information to guide you.

How many hours are on the engine? Do you know anything about its history?

 

[North Idaho Wolfman]

Get the coolant out of the cylinders!!!!!

I think your looking at this backwards, looks to me that #2 was the only one firing and #1 and #3 were washing.
That looks to me like they have been over fueling those pistons and not burning properly, bad injectors.

Pull the oil drain plug and put a cup or so of acetone or lacquer thinner in each cylinder, and see if any leaks out the bottom of the pan.
If you get none or very little and the cylinder walls are smooth don't bother doing rings, because that isn't the issue.

Have the injectors tested, as I'm betting that's your issue.

EDIT: Relooking that the pictures, #3 is definitely being washed (can't see others clearly enough) and very likely has ring, liner damage.

 

[JerryMT]

Here are the only other 2 pictures that I have at the moment. Again, while it's difficult to see the light gray color of Piston 2, you can clearly see that it is matte/dull on top, while the others are black and have an oily or sooty sheen to them.

View attachment 39100

View attachment 39101

# 2 looks like it has some discoloration where the head gasket seals. Could that be an indicator of the head gasket leak?

 

[SidecarFlip]

I would have bench tested the injectors before pulling the head. personally, I think you did overkill but the one cylinder may have wall damage.

My philosophy is do as little (disassembly) as possible to diagnose the issue and then proceed. Deck look fine to me. Don't think it was a head gasket issue.