"Breaking" rod big ends...

[rjamesohio]

I watched a video on manufacturing new BMW moto engines yesterday and was amazed to see how they split the big ends for rods. I'm still scratching my head, but maybe some of you enlightend fabricators can vouch this would actually work....

They manufacture the rods with both ends closed. Then - to get the split into the big end so they can be assembled to the crank they have special tooling that 'wedges' into the big end and creates a split by applying pressure.

I am amazed that they can control this 'cracking' process so precisely. I don't know how it works, but it is some amazing stuff.

Has anyone ever heard of this and can you explain how they control the splitting with such precision such that is accurate for this application?

BTW - the reason they do this is to have each and every rod be a perfectly matched big-end; the 'break'  apparently creates a precision fit un-matched by milling or other machining methods.

Ron

[oldbike54]

 This process isn't new , Honda has been doing it for years also , and probably every other major manufacturer . It gives a really precise mating surface .

 Dusty

[Aaron D.]

I think McCulloch invented the process.

[nc43bsa]

Link to the video?   

[rjamesohio]

Link to the video?

https://youtu.be/Z2DGhCk2aFo

The rod process is around the 25 minute mark but the entire video is fascinating to watch.

[kirby1923]

I think McCulloch invented the process.

Yes and not only that they produced a 4 cylinder opposed drone engine w/out any rod caps at all!

clever, less weight.

:-)

[bigbikerrick]

Fascinating video! Thanks for posting.
Rick

[LowRyter]

The Chevy LS motor V8 like in Camaro and Corvette as well as Mustang V8 use cracked rod caps. 

[oldbike54]

I think McCulloch invented the process.

 A slightly different process , those were roller bearing engines , the races were case hardened steel . Plan bearing rods require a different process .

 Dusty

[John Ulrich]

The Chevy LS motor V8 like in Camaro and Corvette as well as Mustang V8 use cracked rod caps.

Anyone passing thru Buffalo NY, stop at the GM Tonawanda plant to see this in person.   

[Matt Story]

I have the impression that the technique is decades older than this 1984 GM patent I searched which is presented as an improvement to the process.

https://patents.google.com/patent/US4569109

[rjamesohio]

Anyone passing thru Buffalo NY, stop at the GM Tonawanda plant to see this in person.

John - they are actually a customer of mine but they never showed me this process. Pretty cool though seeing all those LS blocks and heads EVERYWHERE.

But - I'd never seen this process before. I'm hoping someone can explain how they control the cracking so tightly - that still boggles the mind!

[Matt Story]

The rod is scored on one or more sides where the fracture is intended to occur.  It's akin to scoring glass before its 'cut' or maybe even drywall.

An earlier patent from 1948 was referenced in the other patent;

https://patents.google.com/patent/US2553935A/en

[John Ulrich]

John - they are actually a customer of mine but they never showed me this process. Pretty cool though seeing all those LS blocks and heads EVERYWHERE.

But - I'd never seen this process before. I'm hoping someone can explain how they control the cracking so tightly - that still boggles the mind!

See if you can tag along on a club tour.    My Corvette club got the royal treatment.  They had a lifelong employee (retired) do the tour... excellent man.  Knew everything about the place and processes (the ones for public only).  He was on the line when the last 427 went down it.

[cliffrod]

Knowing less about this specific process than splitting crystalline material in general, it's fairly straightforward to produce an accurate break in specific brittle material with a known or predictable crystalline structure.  A casting is generally easier and more predictable to break than a forging. Providing or producing a score or relief as a stress riser to direct the break is SOP in certain methods where accuracy is a priority.  These methods applied to metal are simply a rehash of stone work.

As metaphor, it's easier to accurately break or split much harder granite (igneous stone, analogous to a casting) in two planes than it is to split softer marble (metamorphic stone, analgous to a forging) in any plane.  Very dynamic work can be produced when it's done properly, far beyond a small break that measures approx 1/2" square.  This 6' tall granite memorial was sawed perfectly flat when I began work.  The method is called Shell Rock Pitch.  All breaks end perfectly at the sculpted details.  No tool marks remain on the broken stone and nothing artificial is done to camouflage them.  It's all virgin stone.  100% success or 100% failure.  My cousin and I still do it professionally, but we are the only ones.  It is considered to be a lost art.  Very cool stuff and the ultimate extension of splitting technology & methods being done long before 1948....





Some materials can be temperature treated (hot or cold) to an enhanced state of hardness (also typically more brittle).  Metals offer different resource than stone because some can be heat treated to make them brittle & easier to break, then annealed to a different state of temper where toughness over brittleness/hardness is an asset.  breaking rod ends makes sense.

[boatdetective]

Yup- the process is common enough in large diesels also. As I recall, there are tradeoffs with cracked rods. Some builders machine mating serrations in the rods and caps to achieve roughly the same rigidity when the assembly is bolted up. The other technology becoming more common is TTY (torque to yield) bolts.

[LeRoy]

In the video from 25:17- 25:30 the rod cracking process is shown and explained:
"In the cracking machine the eye of the conrod is lasered to create a predetermined cracking point. A wedge then breaks into two halves. Through this special procedure perfect formed closure is obtained."
As is evident from some awkward English phraseology and mis-pronunciation in other areas of the video, the English language version is an imperfect translation from the original German. [https://www.youtube.com/watch?v=ycJvrmodggM] Thus, while the quotation above is spoken in English, the words have the kind of awkwardly literal flow found in a Google translation. The German original is much more precise. Still, you get the idea.

Having been involved in an earlier life in producing, narrating and translating similar videos, it irks me to find sloppy, inaccurate or misleading voice-over. This often comes from a script writer (and narrator) who is insufficiently familiar with what is being filmed or shown. It can also be the result of a literal translation, rather than actually conveying the true sense of the spoken words. So, pardon me if I whine a bit about a few things:
 - The description of the cracking process is a good example of literal translation. It gives you an idea of what is going on but fails on several points to clearly state the process and outcome.
 - In the English video the raw conrod is referred to as a cast part. In the original German the raw part is referred to as a forging. Sloppy translation.
 - Similarly, the raw crankshaft is referred to in English as a cast part. In the German original it is called a forged blank (geschmiedete Rohling). More sloppy work.
 - The title screen states: "Exceptional Engineering The World's Biggest Motorbike Factory." This claim is not part of the original German version. I'm also more than skeptical, considering that companies in China and Japan out-produce BMW by a huge factor. And I expect that they do it in much larger factories.
 - At several points in the video it refers to the BMW factory in Berlin as "Germany's only motorcycle factory." It's a quibble, and cottage industries by comparison, but I'd ask the folks at Horex and Maico about this.
 - The paint's clearcoat is referred to as clear varnish, another Google-style literal translation.

Sorry, I'll stop whining now.

[Rough Edge racing]

 Not a fractured steel rod, but how The R&R aluminum rods in my race Triumph 650 are constructed to prevent fretting on the joint..

           

  I believe that only powdered metal forged rods are fractured ?..Higher performance forged solid steel rods are not fractured but machined in the usual fashion.