Why is one 340 connecting rod bronze color?

[JoeSBP]

so going with the theory of multiple suppliers, with different SOP's for each supplier, a mixed bag of connecting rod colors is the result

I say this myth is plausible.

 

[lilcuda]

It was undersized and they sprayed metal to make it in tolerance....

This is correct. If it the big end was too big, they would just dip 'em real quick and re-hone them.

 

[lilcuda]

Wrong. Copper is way soft and would not hold up to the beating of a rod journal or piston pin can dish out. Copper is the material but it was done merely for corrosion resistance. I have seen engines with all of the rods copper coloured. The bean counters surely put a stop to it. J.Rob

Not true. It's for size. Why would only one end of one rod in an engine be plated copper for corrosion resistance? Makes no sense.

 

[mguner]

This is correct. If it the big end was too big, they would just dip 'em real quick and re-hone them.

Except that there is no sign of the copper where the bearing rides only the exterior surface. That lends credence to the use of copper plating as an inhibitor of the carburizing process so that only the bearing area gets hardened.

 

[lilcuda]

Except that there is no sign of the copper where the bearing rides only the exterior surface. That lends credence to the use of copper plating as an inhibitor of the carburizing process so that only the bearing area gets hardened.

I reconditioned hundreds of rods in my 10 years as a machinist. I have personally honed the big ends of many rods where the bearing surface had copper all over it. I've pressed factory pistons off of rods and found the honed pin bores with copper in them.

It's done for size, trust me.

 

[krazykuda]

Did you hear about the Polish Olympian that won a gold medal and had it bronzed????

 

[JoeSBP]

I reconditioned hundreds of rods in my 10 years as a machinist. I have personally honed the big ends of many rods where the bearing surface had copper all over it. I've pressed factory pistons off of rods and found the honed pin bores with copper in them.

It's done for size, trust me.

This post is about why the whole rod body is copper plated. I'm not saying that don't plate the big/little for clearance, but I kinda doubt they quote the whole thing for clearance..

 

[66fs]

I reconditioned hundreds of rods in my 10 years as a machinist. I have personally honed the big ends of many rods where the bearing surface had copper all over it. I've pressed factory pistons off of rods and found the honed pin bores with copper in them.

It's done for size, trust me.

All the original copper coated rods I have seen had copper in the big bore. Total rod coating is all I have seen. I figured they needed the extra weight to get them to balance correctly. I am a rod racist, if I get a copper coated rod I get rid of it.

 

[mguner]

Crank Works - CWI Pro Rods

Heat Treatment
Our rods start with a copper plating of the non-critical areas. They are then heat treated to stringent specifications by a Nadcap, ISO, and AMS certified heat treating facility. This process substantially hardens the rods for increased strength. From there, the rods are stripped of their copper plating so that they can be properly shot-peened.

Apparently nobody bothered to read this or follow the link so here it is again...... They remove the copper before shot-peening so it is done to all rods prior to heat treating so that only the bearing and pin holes get surfaced hardened from carburizing and the rest of the rod will bend before breaking.... Apparently some of the OEM rods skipped the removal process and or shot-peening. The proper way to size rods is simple and would be a lot cheaper than copper plating. Think about it. If the rods were "dipped" then the cap and rod mating surfaces would be covered too (defeating the purpose of adding metal)and still require machining which is the way to resize the rod anyway.....

 

[66fs]

Apparently nobody bothered to read this or follow the link so here it is again...... They remove the copper before shot-peening so it is done to all rods prior to heat treating so that only the bearing and pin holes get surfaced hardened from carburizing and the rest of the rod will bend before breaking.... Apparently some of the OEM rods skipped the removal process and or shot-peening. The proper way to size rods is simple and would be a lot cheaper than copper plating. Think about it. If the rods were "dipped" then the cap and rod mating surfaces would be covered too (defeating the purpose of adding metal)and still require machining which is the way to resize the rod anyway.....

Those are not OEM factory big number production rods. I have seen my share of copper coated rods and that does not appear to be what happened. I did not work at the factory making rods, and do not know for sure. What I stated above is what I believe.

 

[Krooser]

Way old post here and quite a few more covering the same subject... I found some info that sez the copper is plated on the rods to protect them from the carbon...

Here you go gents, has nothing to do with corrosion resistance, it revolves around the hardening process. Or to be more precise, preventing the hardening process. It allows you to have hardend bearing surfaces, while preventing the hardening of the full rod body, so she will bend, rather than fracture. What did we ever do without the Google machine?? Grab a cup of coffee and enjoy the read...

...A connecting rod in an internal combustion engine provides linkage between the piston and the crankshaft. Particularly in two stroke cycle internal combustion engines, this linkage is done in a low lubricant environment. To accomplish this linkage, the connecting rod generally uses rolling element bearings between the crankshaft and the connecting rod at a first, large end of the connecting rod and also between the piston pin and the connecting rod at a second, small end of the connecting rod. The first, large end of the connecting rod includes a large end hole. Conventionally, after a rod is forged or cast, the rod is cracked in a brittle manner to form a two component connecting rod that is assembled on to the crankshaft through the large end hole. Thus, after cracking, the connecting rod may be reassembled with bolts in a manner that gives optimal registry. Cracking of connecting rods is known in the industry.

It is also known that the connecting rod may be forged from a low carbon steel alloy having, at the very least, less than 0.70% carbon by weight, and usually having less than 0.20% by weight. However, in these conventional connecting rods, the rolling element bearing cannot successfully run on the forged surface because the low carbon steel is not strong enough to resist mechanical deformation caused by the load transmitted from the piston through the roller bearings during the combustion process. To resolve this problem it is known to carburize low carbon steel connecting rods to increase the carbon level near the surface area. The higher carbon level material can then be heat treated to form a specific microstructural constituent known as martensite.

Carburizing is the addition of carbon to the surface of low carbon steels at temperatures generally between 850° and 950° C. (1560-1740° F.) at which austenite is the stable crystal structure. It is known that austenite has a high solubility for carbon and therefore it is ideal to carburize at the austenite temperature. Hardening of the carburized surface is accomplished when the high carbon surface layers are quenched to form martensite. Thus, the carburization process allows for a high carbon martensitic case with good wear and fatigue resistance to be superimposed on a tough, low-carbon steel core.

During the martensitic heat treatment process after carburization, the low-carbon steel connecting rod undergoes a solid state transformation. Initially, the part is in a body centered cubic (BCC) structure at room temperature. The BCC structure is a fairly soft metallic state and is only able to dissolve a limited amount of carbon. During the heat treatment, the part is heated until it reaches a temperature where the low energy condition of the material is preferable to transform into a face centered cubic (FCC) structure. In the FCC structure, many more carbon atoms are able to fit into the interstitial portions of structure as compared to the BCC structure. After the carbon molecules have diffused to the interstitial positions, the part is rapidly cooled or quenched. During the quenching process, the part is transformed at a temperature where the structure is generally of the BCC type. However, if the cooling is sufficiently fast enough, then the carbon atoms do not have enough time to diffuse from the interstitial positions of the FCC structure, and the carbon atoms remain packed in the interstitial positions. At room temperature, the diffusion coefficient of carbon is very low and carbon will essentially be trapped in the position it is in. Since the BCC structure cannot contain this much carbon at room temperature, a third structure, martensite, with a body centered tetragonal (BCT) structure is formed. This crystalline structure has a very high amount of internal stress. Due to this internal stress, the product is extremely hard but brittle, usually too brittle for practical purposes. This internal stress may also cause stress cracks on the surface of the product. From the quenched condition, the part is tempered to increase the toughness, but only slightly, as a surface hardness of 60-63 hardness Rockwell C is desired. The tempering process is well known to those in the art.

Forging is a manufacturing process where metal is shaped by plastic deformation under great pressure into high strength parts. There is no melting and consequent solidification involved. Forging's plastic deformation produces an increase in the number of dislocations resulting in a higher state of internal stress. This strain hardening is attributed to the interaction of dislocations with other dislocations and other barriers, such as grain boundaries. Simultaneously, the shape of primary crystals (dendrites) changes after this plastic working of the metal. Dendrites are stretched in the direction of metal flow and thus form fibers of increased strength along the direction of flow.

Conversely, the manufacturing process of casting consists of pouring or injecting molten metal into a mold containing a cavity with the desired shape of the casting. Metal casting processes can be classified either by the type of mold or by the pressure used to fill the mold with liquid metal. Since casting is a solidification process, the microstructure can be finely tuned, such as grain structure, phase transformations and precipitation. However, defects such as shrinkage porosity, cracks and segregation are also linked to casting's solidification process. These defects may lead to lower mechanical properties in some castings. Subsequent heat treatment is often required to reduce residual stresses and optimize mechanical properties in cast products.

The connecting rod is machined to a near-net shape before the heat treating process. This is done because the cost to machine large amounts of hard material is costly and it is also difficult to create the hardness profile that is required for the part. Unfortunately, the solid state phase transformation distorts the connecting rod. Particularly, this distortion occurs during the quenching operation of the current process when the crystal structure changes from FCC to BCT. Such connecting rods are measured for distortion and straightened by bending. Accordingly, it is desired to create as little distortion as possible of the connecting rod from heat treatment through the phase changes. Ideally, the distortion is limited to less than the final grinding allowance. Thus, in conventional connecting rod manufacturing, the connecting rod has to be straightened before it can be used. Such straightening is a non-value added operation during the manufacturing process of a connecting rod.

Problems also arise if the connecting rod is completely carburized. The section of the connecting rod between the ends usually has a configuration of a thin-walled I-beam. Carburization of the thin-walled I-beam results in an unfavorable through thickness hardness condition. While this condition has good strength properties, it has poor fracture toughness. Thus, the connecting rod is subject to brittle fracture from any impact type loading, and an engine misfire event could cause a fractured connecting rod.

To address the through thickness hardness condition, connecting rods are normally copper plated. Since the diffusion of carbon in copper is very low, the copper effectively masks the carbon and prevents diffusion. After the copper plating process, the connecting rod may be selectively machined to remove the copper in areas where the part is to be carburized. As aforementioned, these areas are typically where the bearing rollers contact the rod at the thrust faces of the first and second ends of the connecting rod. Since these areas have to ultimately be machined, the copper plating is not considered to be a value added operation.

 

[MoparMike1974]

Here is another stumper. I have found that many distributor hold down clamps are also copper plated.

 

[66Dvert]

These are the comments I found on google...

dipped in copper at the factory to bring it into weight specs.
the copper flash plating was to fix rods that got a few tenths too big when they were honing the big end

GM, and Chrysler do it quite a bit, though I cant say I have ever seen a copper coated Ford rod. It was done at the factory to save rods that were finished just a hair too big. Dip them in the copper and you can get them back to the correct size. I do not beleive any rebuilders do it, it would not be cost effective. I bet I see at least 5 or 6 rods each year that way. Does not seem to hurt anything at all.

ding,ding,ding. winner here. (but not on the weight thing, just the resizing and all big 3 automakers did it, I knew one of the shops owners that replated em and it was a mainly a ford vendor but they did GM and Chrysler too.)
Got laid off at my McGraw glass plant and was shipped to Trenton engine, Detroit Axle and Dodge main for a few years before I could go back to the glass plant so I learned a few gimmicks they did to save money.
I worked at Trenton Engine plant (worked on the rod line for the V8's) running the natco's that did the piston small end right before that went into the broach machine for the big end. If either end didn't make final inspection and was under the .02 oversize limit they went into a bin and when the bin was full it was shipped to the platers to get resized, returned and re-ran through the 2nd and final honing to correct size. Guess what color they were? yup copper. over the .02 limit they went to scrap. some big ends were done due to operator error or just plain dull tooling (broaching them usually either works or tears the crap out of the big end and ruins the rod), but mostly for the small end since the pin is a press fit and needs to be tight.

 

[JoeSBP]

Hmmm. So if the rods are copper plated to prevent the rod body from being hardened, at what point would that copper be removed? When they were tossed into the NO-GO bin, were they still copper platted? At what point do the rods get shot peened?

 

[Krooser]

Hmmm. So if the rods are copper plated to prevent the rod body from being hardened, at what point would that copper be removed? When they were tossed into the NO-GO bin, were they still copper platted? At what point do the rods get shot peened?

Are production rods ever shot peened? If so why was 'shot peened' rods such a big deal for the first 50 years or so of hot rodding before the atermarket got involved? I remember getting my stock rods shotpeened because the factory units were not...

I would imagine the copper was removed after being heat treated maybe by being blasted, going into a shot tumbler or maybe by running thru an acid bath?

Don't know... just asking.

All I know is I'm taking some copper rods to my engine guy this week to be sized and have new bolts installed... these will replace the one's that were damaged during the last engine failure.

 

[66Dvert]

Hmmm. So if the rods are copper plated to prevent the rod body from being hardened, at what point would that copper be removed? When they were tossed into the NO-GO bin, were they still copper platted? At what point do the rods get shot peened?

?? no production rods at Trenton engine during the time I worked there were ever shot-peened. They came (raw blanks) in a bulk bin that hit 8 different workstations to process through the system.
1. blanchard mill to grind the sides to spec on the rods. (it's fun when a 400lb grinding wheel starts to chunk off and vibrate, can you say run for your life and keep going at least 100 yards or you WILL get hit.)
this is a tiny one that is similar to the cap blanchard. 18" tall and 42" in diameter. the rod blanchard was 24" tall and 48" diameter.

2. then on a overhead conveyor to go to the 4 natco's that drilled the wristpin end.
3. broached on the big end size and cap mating surface. (no caps on yet)
4. rods bolt holes and bearing locator drilled and ground right after the broach for rod bolts and mating surface
5.Caps went similar to the rods Blanchard mill for the sides, natco or bhures to drill the cap end and the bearing locator groove then through a smaller broach to do the bearing surface.
6. Cap and rod are now matched using a bolt press and torqued to spec. hung on the conveyor going through a washer to go to the next station.
7. major honing station for both the wristpin adn crank end. rehung and rewashed to final hone.
8. final honing and gauging (good goes on and bad hit 1 of 2 bins (under.020 or scrap)

copper rods come in from the platers in bins and only go through the final hone and gauging then on to the engine assembly line.

 

[stixx]

Awesome in depth information!

 

[JoeSBP]

I’ve heard that the resizing process can misalign the ends.
How are they trued in a mass produced setting?

 

[66Dvert]

I’ve heard that the resizing process can misalign the ends.
How are they trued in a mass produced setting?

Resizing in the mass production line just wasn't done(other than the copper plating 1 time only).
The rough hones at the rank end did a side hone on both rod and cap to true up any mismatch in width and just the wrist-pin hole was honed to rough size. go,nogo(checked in final hone).
Final hone did the same except in much finer tolerances. if plated rods didn't meet sizing then is was scraped. It's all about the cost of the rod vs amount of labor to make the rod right.
I think resizing in the aftermarket is they take a bit off the cap or rod mating surface to make it tighter and then have to re-hone the inner bore to make a circle to spec again. The factory would never do that since it take too much time and labor, making another rod was so much cheaper to produce.

 

[Junior340]

This is good to hear as my 340 has one rod colored the same and I never knew the reason or reasons.
thanks

 

[pishta]

66Dvert, where is the Looney tunes industry music while reading this?

 

[Junior340]

 

[nm9stheham]

That is very interesting that the ends are broached for the big and small holes. Fast, but sure would seem likely to leave some stress in the materials. Not surprising that it either worked or destroyed the piece; that would take a lot of force to broach!

 

[RustyRatRod]

I’ve heard that the resizing process can misalign the ends.
How are they trued in a mass produced setting?

Well that's certainly wrong. Proper resizing assures perfect alignment and roundness. That's what the process is designed to do.

 

[JoeSBP]

I meant the copper plating process, not the actual machining.