When big engines blow up

[rondog]

"Here Bubba, hold mah beer. We'll get this sumbitch over the hill".

[mcantar18c]

One thing I have learned in mechanics. The second you think there is something wrong, stop. Best example is detonation. If you hear it knocking or the computer shows, don't push it, fix it.

If this guy had thrown a wrist pin. Well that is bad news. But driving it longer with all the metal bits crunching through other parts of the engine or the cuts back on the amount of salvageable parts. Who knows, maybe the block could have been saved and just over bored a little. I am not an expert on big engines by any stretch. Just using stuff I have learned from turning wrenches in the past.

I learned the same lessons and came to the opposite conclusions as you (shocker).
If there's internal engine damage, its usually easier and cheaper to simply replace the engine. The last instance I had was with my 79 CJ7. Threw a rod on the highway about 7 miles from home. Pulled over, popped the hood to check it out, decided it was f*cked and said screw it and drove home. It would have cost me hundreds in parts and labor for new pistons and all that goes with them, to have the block machined and bored out, etc. I paid $100 for a complete, running replacement long block, swapped it in, and it was good as new. Then I made $200 off the blown engine between selling good parts and the scrapyard.

[nynco]

I learned the same lessons and came to the opposite conclusions as you (shocker).
If there's internal engine damage, its usually easier and cheaper to simply replace the engine. The last instance I had was with my 79 CJ7. Threw a rod on the highway about 7 miles from home. Pulled over, popped the hood to check it out, decided it was f*cked and said screw it and drove home. It would have cost me hundreds in parts and labor for new pistons and all that goes with them, to have the block machined and bored out, etc. I paid $100 for a complete, running replacement long block, swapped it in, and it was good as new. Then I made $200 off the blown engine between selling good parts and the scrapyard.

Well, may be true with your engine. Something tells me a new block in that Semi is not so cheap. Blocks are not always cheap nor readily available for all engine types. Esp newer cars. If you got a common car, well that makes life easier. Regardless, you are talking about a thrown rod. When you got metal running all over the wrong places, then you got problems going to all parts of the engine too. Drive it more and perhaps you need a new head too. Pistons banging against a head over and over and over will kill it. Look at the face of the head from constant impact damage. It looks like the guy lucked out and did not bend a valve. I myself would most likely replace those valves on that cylinder to make sure. Drive it more and you could send metal into the oil pump. Lock your oil pump and the whole engine is toast. Stop and you avoid further damage and can salvage more, thus lowering your costs.

[nynco]

the wrist pin was the root cause of failure... started puking oil into the intake and the engine ran away before it f'ed up the piston enough to lose compression.


The thing sounded horrible so close to throwing the rod the bearing cap bolts stretched and the bearing came loose and was hammered flat. and was just spinning in the journal causing even more problems. starving the rod of oil just compounding the issues. A while back we had a Cat engine that drove in with a broken crank.

DFBrews just said that the wrist pin went bad and driving it more compounded the issues.

DfBrews... whats the story on that piston crown. I have never seen a design like that. I am referring to the cone and what looks like a strange internal pocket around that. Is that to create some type of swirl to better the burn?

[mcantar18c]

Eh, the way I see it... you need to bore the block out anyway, which means machine work + new pistons. If you're doing the machine work on the block you may as well get your head worked over too. Since you're getting new pistons, you'll likely be getting new rods with it and you'll need new bearings with all of this. Also, you may need to machine your crank if it was damaged.
At this point, you may as well throw a whole new engine in there IMO.

DfBrews... whats the story on that piston crown. I have never seen a design like that. I am referring to the cone and what looks like a strange internal pocket around that. Is that to create some type of swirl to better the burn?

Use your google fu. Search for things related to diesels and high-compression racing engines. The information is out there and easily accessible.
Basically, yes, it helps to swirl and mix and compress the air-fuel mixture. It also has to to with the combustion chamber itself, but google will explain all of this to you.

[nynco]

Eh, the way I see it... you need to bore the block out anyway, which means machine work + new pistons. If you're doing the machine work on the block you may as well get your head worked over too. Since you're getting new pistons, you'll likely be getting new rods with it and you'll need new bearings with all of this. Also, you may need to machine your crank if it was damaged.
At this point, you may as well throw a whole new engine in there IMO.


Use your google fu. Search for things related to diesels and high-compression racing engines. The information is out there and easily accessible.

Is fu. supposed to mean f*ck you?

I have seen high compression pistons just not like that. I am not as familiar with big rig engines nor high performance diesel internals. Forgive me for asking questions so I could learn...

[mcantar18c]

Is fu. supposed to mean f*ck you?

I have seen high compression pistons just not like that. I am not as familiar with big rig engines nor high performance diesel internals. Forgive me for asking questions so I could learn...

No, google fu like kung fu. As in, a skill or an art form, one that you should have mastered in this day and age. But if you'd like to take it as f*ck you you're more than welcome to.
The reason I told you to google it is that I, and I'm sure the OP is on the same page with me, do not want to explain diesel mechanics to you and everything necessary to give you a full understanding of what you're asking, especially when all of this information is pretty easily accessible.
Here's some links to start you out...
http://www.enginebuildermag.com/Arti...l_pistons.aspx
http://www.dieselbombers.com/general...n-designs.html
http://saeeng.saejournals.org/content/1/1/913.abstract

Actually, here's a little quote from that first link for ya...

The combustion chamber in most diesel engines is actually in the top of the piston rather than the cylinder head. There is a bowl-shaped recess that swirls and compresses the air as the piston comes up

And another one from the 3rd link... you probably won't understand half of this but it explains the purpose of a bowl/cone... actually it really just talks about the advantages/disadvantages of a small bowl vs a big bowl, but you'll get the idea.

The data show that piston-bowl diameter influences in-cylinder mixing and pollutant formation processes by altering jet-jet and jet-wall interactions. When the fuel jets impinge on the bowl wall prior to ignition, adjacent jets merge, forming fuel-rich regions where soot formation occurs. By using a larger diameter bowl, wall impingement prior to ignition is reduced and delayed, and mixtures are leaner throughout the jet. However, a greater fraction of the jet becomes too lean for complete combustion. By using a smaller diameter bowl, a strong jet-wall interaction pushes the fuel-rich jet-jet interaction regions into the center of the chamber, where mixtures are predominantly lean. This reduces net soot formation and displaces fuel-lean regions of otherwise incomplete combustion into the combusting regions near the bowl wall.

[nynco]

McCantor, thank you for pointing me in the correct direction in regards to the diesel stuff. I also learned the term google kung fu. So thanks for that too. I will read some of the links over.

[nynco]

I follow most of it, but the term "jet - jet" is throwing me. Is it referring to dual injectors?

[mcantar18c]

Atta boy.
Now just one question. How do you manage to spell my name wrong when its written right the f*ck in front of your face?