Anyone have a picture of the setup for weighing the rod ends separately? Is it as simple as supporting the rod horizontally with one end onthe balance and one on a solid support?

The only way I have ever seen it done proplerly is on the balancing scale made just for the purpose in a well equiped automotive machine shop (like ours) This is expensive professional grade equipment and the only way to do this job.

From what I remember from my younger days... 26 or 27 grams to an ounce. so 1/2 gram is GOOD.

I have very accurate balances available to me. I would hope I caN replicate the setup. The only two ways I can think of are the one already mentioned (supporting the end not being weighed such that the axis through both ends is horizontal) or having the end not being weighed pivoting on its bearing surface and the end being weighed on the scale pad.

THe rod is horizontal. The one end on a scale, the other on an ideal pivot, ie no friction so that only the end on the scale is weighed. Anyone with a good scale and any decent ball bearing that will fit into the other end is equiped to do the job. A level for the horizontally challenged could make a difference, but only minor.

Yeh and 1/2 OUNCE is good, 1/2 gram is, well, really really good.

The following photo shows how the big end of a rod is weighed on a commercial rod balancing setup.

First the big end is weighed, the lightest rod becomes the "standard" that all others must match.

All the big ends are machined to weigh the same, by removing weight from the big end. Usually by grinding from a pad specifically provided for this purpose or by even removal from the bottom of the rod.

Finally the small end is machined to match the overall weight of the rod to the lightest or standard rod. The reason the small end is not weighed like the big end is that it isn't necessary. Why? Because if all the big ends are the same and all the small ends are the same, the overall weight must also be the same. THerefore if the overall weight is the same, the small ends must also be the same. or in other words you can do it either way, but the overall is easiest.

For the math types:
Total rod weight = big end + small end

http://forums.pelicanparts.com/uploa...1131510693.jpg

http://forums.pelicanparts.com/uploa...1131510875.jpg

note that ball bearings are used to support both ends of the rod. The rod is perfactly horizontal and the supports are adjustable so that no side loading is possible. Any home made fixture could easily do the same thing. Even knife edges could be used instead of ball bearings. The big round adapter also seems to supurfulous, ie any bearing should work, just so no side load is present. No magic at all just a simple scale. like frys sells for $10 would do as good as this big buck contraption.

Thanks for that picture. I can replicate that close enough.

An important PS

The small end is hung from a short vertical length that has a bearing on both ends. TO tell if there is a horizontal load one just lifts up the small end and sees if the vertical support wiggles or moves. If it does, then the horizontal support distance is adjusted until the small end can be lifted without any movement of the small end vertical support.

In my shop we balance rotating assemblies to a tolerance of 4W/N where W = the weight and N= the speed. That is the API tolerance that was developed from submarine technology where vibration = noise = boom. That is about twice as tight as the ANSI recommended tolerance. Balancing to a tighter tolerance than that doesn't make and difference, it just wastes time and money and gives the uninformed a warm and fuzzy.

One of my customers asked me if I would balance his stuff to 2W/N. He figured that tighter is better. It aint. I told him to just send me a check for an extra $1000 and I would pretend to do what he asked. My balancing machine (Schenk-Trebel CAB 802, worth about $80K with the stand) simply isn't accurrate at the tolerance requested so even if it said we hit the tolerance we would be fooling ourselves and the customer. I have about $10k worth of calibration equipment just ot make sure it is as accurate as possible.

Tolerances are there for a reason. People who suggest a tighter tolerance than engineered is better usually don't understand the process or theory.
I don't personally perform balancing anymore but when I did run the machines I was pretty good at it. Even had a bunch of them square things hung on the wall with my name on em ;)
Even if the measuring equipment and procedures can repeatedly and consistantly provide an accurate measurement, it is prolly a waste of time and effort. After a point of diminishing returns the effort makes no measureable change in the vibration amplitude or severity.
Did I mention that I also have some square things on the wall for vibration analysis from CSI? ;)

Thanks for the input and insight....if you have the time, could you go into your balance theory a little bit more so some of us not so enlightened can get a grip on w= and n= (speed) I am sure I did not digest that all at once and need an other serving just to make sure I liked it.
A Big Thanks!!

This series of posts is one more reason why choosing Supertec was the right choice for me.

Quality repair and a sense of humor
You have to admit, that is funny.

In all this talk of grinding I have not read any mention of how Porsche themselves balances the rods when new. There are no telltale grinding marks that I have ever observed (unlike many other manufacturers) and contrary to Snowman's assertion 911 rods don't have the customary balancing boss on the bottom of the big end that would otherwise offer and easy place to grind excess weight from.

My understanding for the last 30 years has been that Porsche balances their rods on a lathe by turning a small annular step on the two outer surfaces of the big end. This is the surface that will be adjacent to the crank web when the rod is installed. All the 911 rods I have seen have this small step and in the absence of grinding evidence I took this as gospel.

Does anyone know if this is wrong? Or right?

It seems sufficiently over the top to be a Porsche only affectation. They go all the balancers I have heard of one BIG step better. Not only concerned with end to end balance they are concerned with rotating balance. Again an over the top solution that is one of the reasons we are so enthralled with these cars.

Scott Johnston

How a rod is balanced is not important. As long as the big ends all weigh the same and all the small ends weigh the same, all is well. Usually all the big ends are matched, then the total rod weight is made the same, using only the small end, the overall rod is then balanced. The rods all weigh the same, the big ends all weigh the same and finally all the small ends weigh the same. ITS BALANCED!! It dosen't matter how the weight is removed, or added. Lathe, mill, drill, grinder, file, whatever. Just so you do not take metal off a critical area. 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.

Jack;

Thanks for the reply to my inquiry about how Porsche balanced their rods. What you say makes sense about a balanced rod being a balanced rod and that would be my gut response too. However perhaps we are missing something.

In my experience good engineers don't do things for no good reason.

While many engine designers do leave bosses on both big and small ends of the rods that are clearly for material removal and balancing, Porsche does not. Could we infer from this that Porsche engine designers have used another engineering solution to meet this need? If so why (other than Teutonic oneupmanship)?

Could it be that Porsche felt that, from a structural standpoint, those big end sides were the only place to remove the matrerial? To me that seems the more likely reason.


Scott

Porsche does leave an area on the big end that can be used to balance it. Its not a balance pad per se, but you can grind on the big round piece of metal on the bottom, without harming the rod. Of course you would do this as far around the entire bottom as possible, so as not to make a big NICK in the rod. However Porsche does it is not important, the rods are very close to begin with, so only minor ammounts need be taken from any part of the rod.

In my opinion all rods should be shot peened after all other work has been done on them. This critical step prevents cracks from developing or propagating. Polishing just dosen't cut it. Metal improvement company is the ONLY company that I know of that can competently shot peen rods. Carrillo and the factories may have solid shot peening facilities, but they are not generally available to the public.

If you have anything shot peened and the company does not give you a bunch of slightly bent metal strips back with your job, they were not competently shot peened and may not be as good as a non peened product. These thin metal strips are the only control the company has on their process, if they do not use them, do not use that company.

Porsche doesn't really balance their rods. They actually just assemble weight groups. They manufacture the rods and weight them to determine weight variances. Then they put them into weight groups.
They(Porsche) believe that 4 grams is close enough. We have seen many rods in first time tear down that were as much as 9 grams out from end to end. (Same overall weight).
I know it sound strange but it is true.
We would never run an engine with rods more than 1 gram out and generally get closer (equipment limits) than that. I know it's not necessary but setting up the tools is almost as much work as balancing the rods. We feel that a job worth doing is worth doing right.

What is right? I guess we all have to figure that for ourselves.

I had my rod inspected by a woman recently who reported that it seemed heavy. I let her go ahead and work the rod for a bit, and it seemed like she was trying to take some material off. Eventually, the rod did get lighter. She didn't charge me anything, but she did use a special tool.

woman are the best inspectors...they know what and where to look for...

Snowman says:

"Porsche does leave an area on the big end that can be used to balance it. Its not a balance pad per se, but you can grind on the big round piece of metal on the bottom, without harming the rod. Of course you would do this as far around the entire bottom as possible, so as not to make a big NICK in the rod. "

I don't think you would want to take any significant weight off of this area. That web around the rod cap sure looks structural to me, acting like a weight efficient gusset or flange or web to keep the cap round. Chevy rods and the like have a honking big squarish block on the cap tailor made for grinding off some weight as might be needed. But not the 911 rods I am familiar with. I once had some 911 rods balanced by a shop that does US stuff. They ground a whole lot off some of my rod caps, down to half height on some. The concensus was they ruined the rods. I got another set. It only takes having a rod cap get loose once to make one rather cautious about this part of the engine.

And the rod cap needs all the stiffness it can get, seems to me. I had a top end disaster (was it the piston that pulled apart at the wrist pin, or the valve whose head pulled off? Can't remember), and the rod cap bent so there was plenty of air between the inner mating faces (luckily the good aftermarket bolts, though both bent, held and I didn't lose the case and all the other stuff).

The balancer I usually use is one of those perfectionist crusty old machinist types: we do it my way or you can get someone else to do it. He might polish the cap web a little, but mostly he takes a little off the square corners on top and bottom of the sides by the rod bolts. Presumeably most of the stress is in the cylindrical area around the bolt axis, so these areas are structurally superfluous. A previous post had a picture showing a rod balanced this way.

And this lack of good meat to grind pretty much limits how much you can remove, buttressing the common sensical notion that you should start out with a pretty closely matched set before doing any balancing anyway.

Walt Fricke

The area on the bottom of the rod is not critical, only around the rod bolts is. Sounds like your crusty machinest is taking it off the wrong area. And as Porsche rods are generally balanced pretty darn close to begin with you only have to take off a very small ammount. Of course you must have the rods re shot peened after all machining has been done. All rods should be shot peened. as an aftermarket supplier I would only trust a company called Metal Improvement Company to do the shot peening. Is not that expensive. Metal Improvement Company is a division of Curtis Wright, you know the company that invented airplanes and airplane SI engines.

Rods are really tough. I have rods that have been twisted, by sticking a bar in the small end and holding the big end in a vice. How many twists? 4 complete twists and the rod looks like a pretzil, but it didn't break. Some rod bolts can stretch to several times their original length, without fracturing. But usually with cycling, like an engine does when the bolt is over stressed, will cause a break. If your lucky it will just hammer the rod and crank to junk. The bolt is always the weakest link in a rod so grinding a small ammount from the rod is no problem, as long as it isn't in a critical area like the rod bolt radius.

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.
http://forums.pelicanparts.com/uploa...1162397053.jpg
http://forums.pelicanparts.com/uploa...1162397075.jpg

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?

http://forums.pelicanparts.com/uploa...1162405132.jpg

http://forums.pelicanparts.com/uploa...1162405162.jpg

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.

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.

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

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.

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

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

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.

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.

Be specific: Where am I wrong?


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.

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.

http://forums.pelicanparts.com/uploa...1162603725.jpg
http://forums.pelicanparts.com/uploa...1162603754.jpg

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.

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?

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.

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.

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

http://forums.pelicanparts.com/uploa...1162839660.jpg

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

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

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

http://forums.pelicanparts.com/uploa...1162860590.jpg http://forums.pelicanparts.com/uploa...1162860646.jpg http://forums.pelicanparts.com/uploa...1162860672.jpg http://forums.pelicanparts.com/uploa...1162860691.jpg http://forums.pelicanparts.com/uploa...1162860704.jpg http://forums.pelicanparts.com/uploa...1162860715.jpg

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