Something else to ponder. I have read that the very high hp 7.3 PSD need a girdle on the block because of the flex. The very high hp cummins do not need any modifications to the block. I understand the angle iron analogy but it seems to not apply in the particular instance.

 

I don't know where you got the quote above, but inline 6's sure as heck have counterweights on the crank. Inline 4's aren't inherently balanced and many require a balance shaft. A V12 is just to inline 6's attached to the same crankshaft. Do a little more homework before you post something like that.

 

Thats the thing. I have done my homework.
Hmm that says no balancer shaft. You only need counterweights if something is out of balance. Inline 6s if they are not firing. If they are just turning will make very nearly 0 vibrations. When a conrod moves left it is cancelled out by one moving right. When a piston moves up it is cancelled out by one moving down. If designed properly of course. The only real problem is the combustion event. Which all engines suffer from. And of course torque spin. Some manufacturers will put a harmonic balancer on an engine to help balance out the combustion events. Not to be confused with balancing of the reciprocating mass.
In case that was not clear.
So I was correct. Counterweights are needed on a v8 but not on an inline 6. Generally speaking.

 

I think I may have been wrong about the heat dissipation judging by this. But is sums up everything else nicely. Im guessing the heat loss is out the head.

 

Anyone can cut and paste. I'm talking about doing actual homework and doing some studying on your own. You will find that inline 6's DO have counterweights. The vast majority of inline 4's DO have balance shafts. I can find a lot of things on the internet then cut and paste them here. I will admit that inline 6's are considered to be inherently balanced, as are V12's. V8's can be balanced just as well.

If you would have actually read the article from the website which you pulled the stuff above, www.autozine.kyul.net, you would have seen this: "As you know, all engines have counter weights just enough to balance the weight of crank throws and part of the connecting rods, leaving the remaining weight of connecting rods and the whole, all-important pistons unbalanced." I'll type it that again, slowly this time, so you can understand. All engines have counter weights.

 

Yes but the ability to find pertinent information is important. To cut and paste is useless if it does not apply.
I am unable to get the whole article. Can you supply the link. Many apologies it was my understanding that if you had matched pistons and conrods that weights would be unnecessary. My bad.
This says if you add counterweights to an inline it introduces vibrations. So If this is incorrect. I am confused by this. Could you explain it better. If the engine is balanced why add weight. Wouldnt this unbalance it. Counterweights are to counteract a force. What force is present that needs counteracted if its in balance to begin with? Not being sarcastic. Just curious.

So when you balance a v8 it seems to be at the cost of additional weight.

Also by this it appears that a short stroke inline 6 would be capable of far higher rpms than a counterbalanced v8. Is this true?

 

I went down to the local machine shop to take a gander for myself.

Tell me if my assumptions are correct. What you are calling counter weights are not to balance the conrod piston assembly but to balance the crankshaft itself. Is this correct? The six crankshaft obviously was weighted but it looked like it was to center its own weight while spinning. The v8 crankshaft on the other hand looked like it was obviously weighted to counteract some force other than the crankshaft. So while the inline shaft has fins cast into it to balance it. Im not sure they call it counterweighted. Its only to balance its own out weight.
I got to hold a 5.9 conrod in my hand. Hefty piece. They had a conrod and piston there to a 360 isuzu and the whole assembly with pin weighed about the same as the cummins conrod. Its that big. They said the conrod pin and piston weighs about 10lbs on the cummins. I wonder why they built it so big. Thats a lot of mass to throw around at 3500 rpms. He claimed the conrod would stretch above 3500. It would go back to its original shape but it would stretch. Like a rubber band. The crankshaft alone is over 120lbs.

 

Just to let you know, there is more technical info out there from people who actually do the calculations. A lot of what is out there is incorrect or someone's misinterpretation of the facts. The only engine I know of which doesn't require counter weights is a boxer type engine, where you have two cylinders opposed to each other. In that case each cylinder cancels out the one opposite it.

Just take a look at the crankshaft out of an inline 6. They have counterweights. I tend to feel that the people who designed them have more knowledge about the subject than I have or ever care to have. Check out a Ford 300 I-6 crank. It is well balanced and is legendary for it's long life. It HAS counterweights.

Also this notion of revving is kind of ridiculous. Many modern V8's are able to be designed and balanced to spin well over 6000 RPM's without any problem. Heck, my old-school 460 can wind to over 5500 and it still feels smooth as silk. If properly engineered and balanced, a cross-plane V8 can cancel 1st, 2nd, etc. order harmonics and be very high revving.

 

Diesels have to basically live on detonation while running 30+ pounds of boost. They need to be HEAVY.

 

I have found references to countershafts when talking about inline fours and counter weights when talking about v engines. Do you know the difference? I havent been able to locate a good definition. Once again though it says that inline sixes are well balanced and do not require a countershaft nor any mention of counterweights. http://www.thrashercharged.com/tech_...ne_design.shtm
So I still do not understand.

On edit: I have found a countershaft described in the above article. I would like to see one as it is installed on an engine but I understand its use.

P.S. An engineer would cringe if he heard you say a diesel runs on detonation. Its a controlled combustion event. Detonation is uncontrolled by definition. Using ether on a diesel with a preheat system would qualify as detonation.

 

I realise a lot of info is bunk. These appear to be written by mechanical engineers though.
The same paragraph that said boxers dont require weights also said inlines dont either. So more info that makes no sense.
It said this and then immediately compared it to a boxer. Then said most manufacturers wouldnt be able to make a boxer. Too much work. But the same as a boxer cancells itself out. So too does an I6. As 1 moves up 6 comes down. 2 up 5 down. 3 up 4 down and so forth.

I have owned boxers. Very smooth. Expensive to repair and difficult to work on. They do tend to live long lives though. Must be something in the balance.

A boxer six would not net the same fuel economy as an inline but it has some benifits. Lower center of gravity being the big one. Shorter package but very wide. Try changing the plugs on a 3.0 subaru. I dont think you would be able to do a head gasket without pulling the engine. Tight fit.

I caught something in one of these articles that disturbed me. It said that all diesels should have a bearing before and after each cylinder due to the load characteristics. Especially in high hp apps. I guess its because a pickup is a low load environment that it is not necessary.

 

Okay Heretic,
For the most part I now just let you ramble. You love to parrot web-stuff, that's obvious, and about 50% the time you step into the manure hip-deep. But ... I'll give you some credit if you've been running down to the shop and looking at some hardware ... and I'll impart some engineering knowledge. Class is in session. Now, heretic, remember that no one knows it all, okay. So have grace w/ people, all right? However, give credit to people who have taken the time and years to become educated and experienced. E.g. I threw out some "general" advantages of the V-design. If cummins has gotten 4-valves per cylinder into their design, then good for them.

Okay ...

This guy, Isaac Newton, taught us that objects have a resistance to motion, and tendencies to stay in motion. When the cylinders in an engine move up/down, the engine block has an inertial tendency to resist that, and will move in the opposite direction. Piston goes up ... engine wants to go down & vice versa. Similarly there would be some motion side to side with the slight off-set in the crankshaft. The engine, again, will tend to move sideways in the opposite direction. The up/down would be the major force, the side/side the secondary. A 3rd axis of movement would be forward/backward, but not much happening there. Finally, the engine will experience torques in 3 directions too, just like an airplane ... pitch, yaw and spin, and the engine block wants to counter-act. So ... that's all the forces together. Well ... there's some more, but that's good for now.

Okay, the cylinders in an Inline-6 move up/down and the whole-thing can be mechanically set & balanced to be smooth. Here comes the twist: Some of those movements are caused by an internal combustion. This is now a whole NEW force to add to the equation. If the first cylinder fires, it pushes the engine AND you get an imbalance because it's happening on ONE end. To offset that you can fire cylinder 1 and 6. But then the whole engine is being pushed down.

Here is a revelation: ALL engines are inherently smooth when rotating ... but not firing or combusting. It's the combustion that add's the nasties.

V-designs offer more OPTIONS to deal with and handle these dynamic forces than an Inline does ... generally speaking. This depends on the number of cycles & powerstrokes and other factors which vary from design to design. But with a V, you can try more things to deal with the problem. Off course it adds it's own problems, too.

The one force not easy to "quell" is the spinning degree of freedom ... after all .... you want that coming out the back end to the transmission anyway. Engines shake the most on the spin axis, therefore. (This is where the Cummins has a natural disadvantage. Mine shakes my teeth out ... and my PSD is much smoother ... despite the hooey-fablooey web-tests you keep citing).

So anyway, harmonic vibrations ensue from the combination of the above, and harmonic dampeners (of course) are added. Only ... don't just look on the crankshaft. An inline-6 may, indeed, have very little there. dampeners can go anywhere on a drive train that you want.

Automatics have a natural dampening through the fluid coupler. Another PSD pro there.

I was reading the Dodge.com to check on the 4-valves claim, and I can't find anything ... in fact ... they don't give any info on their diesel at all. The cummins site has a one-page BS-level job. WHERE ARE THE SPECS ON THE CUMMINS 600?

Also found out that the manual transmission on the Dodge Cummins is MANDATORY. It comes standard and you have to order the auto. What a rip off. I bought my Dodge used, and didn't know that.

Okay ... class is over. I don't want to over-educate you all in one thread.

The Ironman

 

Ironman, good post. I certainly believe what you posted knowing your background. There are a lot of websites out there with bad information. That's the one real problem the internet has created. In the past, you had to be someone or have a lot of money yourself in order to be published. Now anyone can be published. I read an article about a year ago regarding the lower quality of term papers at high schools and universities. One of the main problems according to the article was the fact that students get a lot of their information off the internet. Just today I emailed a website that was brought to my attention regarding a part for the 7.3 PSD. There are 2 parts used for this engine, depending on engine serial number, and they had the numbers listed backwards. It just proves how easy it is to "publish" information on the internet that is not necessarily correct. Myself, I'm working on a PhD right now and although it's not in mechanical engineering I'm used to wading through the bad information to get to the truth.

 

The cummins went to 4 valves per cylinder in midyear 98'. The red lettering on the truck says "cummins 24 valve turbo diesel", till 2003 when they changed the badging. The new ones have it too.

 

PS. quit comparing ANY 96' diesel to ANY 04' SUV with a diesel. Its never going to be a fair comparison. Just to be objective like you say you are.