What Is The Hardest Working Part Of A Diesel Engine?

[mike r]

rod bolts

I've heard more than one Cummins mechanic comment on the offset rod in our engines and this stress goes into the bearings. Next choice would be the crank bolts for the flywheel. All that torque gotta go through them.

 

[illflem]

Come on Doc, whats the answer?

 

[Joseph Donnelly]

Connecting rod. The piston and pin weigh over 4 pounds. During overlap, the piston/pin has to be stopped from hitting the head and pulled back down. Even the 4. 7 lb Cummins rod stretches noticeably on that one.



Next time you buzz that B or ISB to 3500+ rpm, think about it. Force on the rod end goes up with rpm2 I've been told.

It's been too long since I took Physics, and I'm sure someone will jump in if that is wrong.



OK what are the other candidates for most stressed part?

 

[C Schomer]

Joe - I'd say the OIL in yours!! And then the filter, trying to get the chunks of soot out! Craig

 

[Andy Perreault]

For the benefit of those who are new to diesel engines, the answer to Doc's question would be the distributor cap and the rotor.

And let's not forget about the flapdoodle on the spanker valve, and that doohicky next to the thingamajig.

Glad I could set the record straight.

Andy

 

[Lsfarm]

What is 'Work'

Hi Doc, you are going to have to clarify what you mean by 'the hardest working'. If you mean the part that contributes the most to the total power output, the answer will be different than the the answer to what part transmits the most power.



Or which part is overworked for what it is designed to do. [the lift pump gets my vote here]



I think this is one of those thought provoking questions without one single answer.



Are you sure you never taught school?



Merry Christmas Doc. greg L

 

[maint.man]

I'm goin' with "Carburator Belt" Isn't that what makes the squalling noise when you shut em' down ?

 

[mike r]

Who's Winning this Poll?

First no Christmas Present I liked( no new transmission guts). Now no clear winner from the judges. I think we are part of a larger conspiracy. Merry Christmas to All , Mike

 

[JSoloman]

You guys are all going to tear into your engines to figure this one out... Doc, you've created a monster!!

 

[Power Wagon]

On the first gen engine, it is DEFINITELY the injection pump. Once you see how incredibly busy that thing is inside, and how fast the parts have to move and just how delicate a lot of them look... Yeah, it's NO CONTEST. At 2500 rpm, the pumping plunger makes 7500 strokes per minute. it moves about 3/8's of an inch and is returned, to the valley of the cam plate by springs. And, for those of us with insane thoughts (like me), it goes even faster...



Later engines, it's the injectors. They suffer through the absolute worst stresses and strains and they are very small and delicate.



My apologies to Joe Donnelly, but the rod and piston are stressed to be strong enough to do what they do without fail. They are big and beefy, and all of us know that broken rods, pistons, or broken cranks are very, very rare.



Failed injectors happen far more often.

 

[drawson]

Your all over looking what really gets hammered in a diesel engine = It's the fuel itself, first it's put under extreem pressure , then it explodes.

 

[illflem]

Good answer Dee, but is the fuel a part of the engine specific to a 5. 9? I think Doc threw us a trick question.

 

[Joseph Donnelly]

I KNOW it was a trick question designed to stir us up



Failure rate vs. level of design overengineering

The hardest working part may also be the most overengineered one. Here, the crankshaft transmits the power for all 6 of those itty bitty pistons



PW--yes some parts fail more often, generally easily replaced ones. I mentioned the connecting rod because people seldom look at it and its bearing. I just did yesterday, on a spare engine, and was surprised at how the huge bearing was worn in a stock 215 hp engine.



We are told how that stuff lasts forever, but in my experience, after 75,000, a valve job is a good idea, and the bottom end experiences wear too. Also the con rod is what transmits the force of expanding gases to the crankshaft, so it sure does work hard--in some engines at least

 

[LarryB]

None of the above mentioned parts will do much work at all without the clutch. I think it handles the most difficult/abusive/thankless job in the whole vehicle. Friction, revs, heat, torque, vibration. This baby gets it all. I can think of no other part that handles this much "work".



Or, you can say that no engine parts do any work. All work is done by heat expansion. All the parts do is transfer or convert that work into vehicle motion (or smoke in some cases).

 

[mike r]

Conspiracy!

I knew it all along. You're just waitin to see how many good engines end up as pieces in the classifieds, then its Merry Christmas for you at bargain prices. Good plan but I think not!

 

[chrgr446]

Originally posted by Joseph Donnelly

I KNOW it was a trick question designed to stir us up



Failure rate vs. level of design overengineering

The hardest working part may also be the most overengineered one. Here, the crankshaft transmits the power for all 6 of those itty bitty pistons



PW--yes some parts fail more often, generally easily replaced ones. I mentioned the connecting rod because people seldom look at it and its bearing. I just did yesterday, on a spare engine, and was surprised at how the huge bearing was worn in a stock 215 hp engine.



We are told how that stuff lasts forever, but in my experience, after 75,000, a valve job is a good idea, and the bottom end experiences wear too. Also the con rod is what transmits the force of expanding gases to the crankshaft, so it sure does work hard--in some engines at least

How about the wrist pin? that little guy is the one that gets the smashing on the power stroke(no not powerstroke) and has to keep the piston from continuing upwards as the rod heads down south.

 

[Joseph Donnelly]

yep, talk about overengineering. That little puppy is about 1. 57" OD, 0. 4" wall, weighs 584 g, over 1- 1/4 pounds. More than a lot of pistons for gassers. Oh, piston, you asked, how about 1280 g depending on which B engine, and that is 2. 8 pounds. Cummins sure went for strength with the bottom end of the B engine.

 

[chrgr446]

WoW, now add in the rod, rod bolts, and rings.

What is the total reciprocating weight 8-10#?

And my wife asks me why I laugh(actually giggle like a school girl) when we blast from 50 to 80 in what seems like nothing flat!

 

[Doc Tinker]

In Conclusion?

[Edited]



Doc

 

[mike r]

The suspence was killing us!

I'm OK with the fact that I didn't win but at least you won't get my engine in pieces! Those patience classes and raising kids are paying off for me. Next Question Please.