Matching rod weights

[Henry Schmidt]

On the Pankl titanium rods the material removed in the balancing process came off the sides of the big end.
By measuring them this conclusion is easily confirmed.
This flies straight in the face of what others have posted here.

There is no indication that any weight was removed from the base of the end cap.
You might also note that the area around the rod bolts is rounded not square indicating to me that the square points (corners by the bolts) on a stock rod may not offer much benefit.

[Henry Schmidt]

Two more rods coming straight out of unmolested engines. First one is 91 3.6. The second one is an 87 3.2.
I read somewhere that you should "trust the manufacturer. They know best."
While I don't blindly prescribe to this principle in this case, why not?

[afterburn 549]

this may not work for the race circuit...( but they have more $$ then I do ) But i did have my beaver take it off the bottom. That was 2 years ago and I flog the crap out of this engine....dont know if it will work for everyone, but dose for me.

[Henry Schmidt]

afterburn

That little critter seems pretty busy

2.7 rods are over engineered (READ HEAVY) and with the low power, minimal RPM potential of your engine, trimming the rod cap is really no issue.

[afterburn 549]

yup, but now after all this info wish I had them shot peened....we shall see.....maybe get ready for mass carnage?? I thoroughly expect someday

[snowman]

The sides is the WORST place to touch the rods. THe big round thing on th bottom does nothing in comparason to hold it togather. If you have ever found a rod that broke, in a primary failure, it will be the rod bolt, or the radius just above the bolt, never the bottom.

[afterburn 549]

my beaver was smart enough to take it off the bottom.....20/20 hind sight for sure

[Jeff Alton]

Hmmm glad when I balance mine I took it off the cap bottom..... Time will tell if that was a good move or not because this will be a 7500 rpm motor and I plan on using it. However, mine were all darn close out of the box, so it took minimal work to get them bang on.

Cheers

[Henry Schmidt]

Originally posted by snowman
The sides is the WORST place to touch the rods. THe big round thing on th bottom does nothing in comparason to hold it togather. If you have ever found a rod that broke, in a primary failure, it will be the rod bolt, or the radius just above the bolt, never the bottom.

Pankl and the Porsche factory would have to be dead wrong in order for snowman to we right. That's an easy call for me.
I will and have done just like the factory for over 25 years. Remember, you can only remove small amounts, 9 grams or less.

Who do you believe, the manufacturer or the guy who makes outrageous claims that anyone can disprove.

"All F1 and Cup teams use Carrillo rods." " Both wrong

Guess who said this?
"The bottom end is generally not critical, the sides of the rods are generally not critical, the top of he rod is generally not critical."

Which is it "the sides are the worst place" or "the sides of the rods are generally not critical"

Talking out of both sides of his mouth.

To be absolutely clear: I don't like the 3.2-3.6 rods. I believe the design is poor for a number of reasons. If performance engines are to be built using 3.2-3.6 cranks I recommend using an improved rod or at least rods bolt.

[snowman]

Henry, I am sorry, you are just plain WRONG. The bottom of the rods is the least sensitive place to remove material. Unless you can produce a written statement from anyone that it is not, shut the f up, because you are dead wrong.

Good luck in producing any such reference.

Carrillo is currently the biggest supplier of rods for any competitive event, period.

I suspect that you cannot believe this, yet Carrillo is the major supplier, in numbers and dollars of all rods used in any competition, period.

Any doubt, contact Carrillo. And if you do, please announce the results here. They are number ONE, period. IN terms of numbers, of dollars. in performance.

ANyone who has Carrillo rods need not worry, every thing else in your engine will break, before the Carrillo rod.

Henry, you need to learn more. Listen to the engineers, they DO know what they are talking about. After all they designed the very same engines you work on. They designed them to do what they do, nothing more. They also designed the F1 engines and all that they are about.

As an auto tech your place is not design, but building a reliable engine, based on every thing you know, but that excludes engineering as you basically have no control over this portion of the production. In other words you have to work with what you have.

What you have is not what the engineers desire, but what the production people desire, not optimum.

Your fine tweaking is a result of experiment, not design. It may be optimum, it may not be optimum. Its what you have done. Engineering provides the real optimum, you need to learn what that optimum is and to strive to achieve it. Until you know what the real optimum is you cannot strive to achieve it.

[Henry Schmidt]

Be specific: Where am I wrong?

Originally posted by snowman
shut the f up

Shame on you

Only small minded people try to suppress differing view points.
I will not succumb to your bullying. I will post my opinions and my point of view and let those who read these post to decide.

I believe it is important to point out where we agree.

1 st : I believe Carrillo makes a great product. I also believe that for most applications they're a great choice.
2 nd : I use your own words to illustrate your foolishness. In turn you use your own words to make yourself look foolish.


Last, you should try to understand, as difficult as it is, that you don't have to be an engineer to understand engineering principles.

[snowman]

Ok Henry here is a link to a picture of a rod with the high stress points shown in color. http://www.easa.aeat.com/case_studies/case_study_pics/connect_rod/Connecting_Rod_Results.JPG Note that the bottom of the rod is blue, ie lowest stress, while the sides, where the bolts go thru have a high stress concentration where the halves join. Even when the bottom is stressed, the stress is spread over a very large area. Compare that area with the much smaller, more highly stressed parts of the rod. You would have do a whole lot of damage to weaken it enough to match the higher stressed areas of the rod.

Here is an indepth article on rods thats quite interesting.
http://www.autosteel.org/AM/Template.cfm?Section=PDFs&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTFILEID=3390

Page 39 of this article shows the critical points of a rod, points 1,2,3, and 4. Even the smallest nick in one of these areas and the rod will break, sooner rather than later.

This article also makes a point about rods. They wear out! They fatigue and eventually break. This is a good reason to always use new rods in an all out race engine. No one can recondition a used rod in any way that will extend this lifetime. How do you tell how much of that life has been lived in a used rod?

There is one good reason not to use a rod that is much lighter than the others. If all the mechanical dimensions are very close, WHY is it lighter? Could it be a big defect hiding under the surface?

As to the side of the rods, the place where the bolts go thru, I kind of suspect that they were designed that way. The area, where the rod halves join is highly stressed. Therefore if makes sense that the rod would be wider at that point.

[Henry Schmidt]

Originally posted by snowman
..............Note that the bottom of the rod is blue, ie lowest stress, while the sides, where the bolts go thru have a high stress concentration where the halves join. Even when the bottom is stressed, the stress is spread over a very large area...............

[snowman]

See those little arrows. Notice their spacing is wide at the bottom, but they get closer togather as you go to the bolt area. The green is a couple shades darker (less stress) than the very light green areas, and much much less than the red areas, thats the highest stress area. Look very carfully at all the pictures. Also think about it, the same stress on a small part and a very big part. The small part is always going to break first.

[Henry Schmidt]

As I've stated many times before, I'm not an engineer but
as far as the arrows go, don't the longer arrows indicate larger(greater) stress?

Originally posted by snowman
....... The green is a couple shades darker (less stress) than the very light green areas...........

Once again your just making ***** up.
In the picture I posted from your link, the legend clearly shows that the light green (teal) represents less stress than the dark green. How do we take you seriously if you don't even get the simple things?

To see the legend for these pictures follow the 2nd link posted by snowman.

[snowman]

No henry, the arrows show that the bottom of the rod has less stress per square inch than the sides of the rod. I am an engineer and I know how to read the diagrams. I am not making anything up.

The critical areas of the rods are the areas that are depicted in RED. Thats where they break. Thats where the sample rods in this paper broke. Think about it, the small end endures almost as much as much stress as the big end, yet it is much much smaller and thiner than the big end. Think about where all the manufacturers add balance pads, at the bottom of the big end (including Carrillo) and at the top of the small end. Those areas and under less stress per square inch than anywhere else, so thats why they put the pads there. The small end also has to contend with bending in addition to the tension. Look at the broken rods in this paper, this is where rods break, why? because those are the most highly stressed, critical areas.

[Henry Schmidt]

Wow let's see that degree. Post a copy, I'm sure we'll enjoy that.

Removing weight from a rod is a function of the rod design. If material is added to the sides of the rod with the intent of using it for balancing then the material should be removed from the sides. If a weight pad is added for the purpose of balancing then the weight pad should be used.

It is obvious that rods are design differently and the the Porsche factory designed their rods to be balanced on the sides.
If they didn't design them that way I doubt they would balance them on the sides.
The rib at the bottom of Porsche rod is not a weight pad.

ENGINEER JACK

[Jim_Brown]

Snowman-

You appear to be basing your argument that the bottom material is less important than the sides on the analysis of stresses that lead to fatigue failures/cracking.

One other design consideration with a rod is the need to prevent excessive deformation that will result in premature failure of rod bearings.

Henry's post showed contours of axial displacement. Based on that post, it looks to me like the critical design consideration for the bottom end of a rod is to provide enough material such that excessive deformation doesn't make the opening out of round.

Because the allowable deformation is small, the stresses in the bottom of the rod will be lower than areas of the rod where deformation isn't as critical.

Deformation of the side of the big end occurs due to elongation of the rod bolts. If you take material off of the sides of the cap (where it appears that Porsche opts to remove material to balance the 3.2-3.6 rods) you are removing material from an area that has little impact on deformation of the big end opening.

Cheers,
Jim

[afterburn 549]

WoW, at least were getting back on track, other then the stone throwing I rate it up there in numero 1 some where

[snowman]

Mr. Brown,

Your analysis is not correct. Look at the 2nd article I cited and look for the RED spots on any of the cycles shown. The stress on those places is far higher than any other portion of the rod. Again I will restate, look where the rods actually broke, same areas as the red spots and none of the red spots are on or near the bottom of the rod. Stress causes deformation. The bottom of the rod is not stressed much, therefore there is little likelyhood of any deformation and very little metal is required to keep the rod round. Look at the small end, its stressed much much higher than the bottom yet there is much less metal there.



The bottom of the rod only has to support the weight of some of the rod and the piston and wrist pin. The top of the rod has to support all the same weigh PLUS the force of the power stroke. The power stroke also causes significant twisting on the rod at the wrist pin and the top half of the bottom of the rod. Far more forces than the bottom has to endure. Note that a high stress point is exactly where the rods join together, much higher stress than the bottom of the rod sees. It would be foolish to ever use this area for rod weight pads. If any elongation of the rod bolts ever occurs, the bolts will break within a couple hundred cycles, in other words a few seconds. Rod bolts must always exert a positive clamping force that is never exceeded by the forces of high rpms. The power stroke shouldn't be anywhere near the worst force on the rod bolts. Locating pins or fractured rod construction must take care of all lateral forces on the rod joint. Twisting is mostly confined to the narrow portion of the rod shaft, as it is the weakest portion of the rod to that kind of force. That’s why many people like H beams over I beams. I beams supposedly present less drag due to slightly better aerodynamics. Grocery getters, like a typical Ford or Chevy were never intended to operate at high power or high rpm so they can get away with using the rod bolt to locate the rod halves. The newer Chevys and Fords use fractured rod construction because they do have to live up to 6000 rpm or more and they have to guarantee the engine (for smog) for 100,000 miles. To accomplish this they had to make a better engine.

approx stress vs color
Red highest about 600
yellow about 480
light green about 350
dark green about 250
blue about 60

Go to the article for more accurate information



The last photo shows the most critical areas in yellow and red.