577 SOHC Post Mortem

[turbohunter]

Also, are the striations where the flaw is or are the striations next to and a result of the flaw.

[WConley]

Doug -

Hard to tell without a close inspection, but it's possible that something happened during processing.  A dull/ broken tool or interruption in machining coolant could have caused a hot spot or tear in the material.  If there was a flaw embedded in the material, and it ended up exposed on the surface (during machining), that would be really bad.  Even a ding or nick in handling can start a problem.   Tough to tell from far away!

X-ray inspection is great for spotting voids / flaws deep in the material.  The surface is tougher for X-ray, because it creates lots of shadows.  That's where magnaflux steps in and shines.  You can see surface flaws or cracks that extend up near the surface very clearly with a magnaflux inspection.  Deeper than about 1/8", I was taught, magnaflux is not effective.

I'll let the real experts chime in, because I haven't done this stuff in almost 30 years.  Been mostly on the design side since then...


Edit:  Turbohunter-  The striations radiate away from the flaw - the epicenter.  Imagine all of those rings surrounding a point, in this case on (or near) the surface.  The crack started at that tiny point, and grew as the rod was cycled.  The striations are witness marks from the crack growing.

- Bill

[turbohunter]

Aah, thank you.
I was 180 out thinking that the rough spot in the middle of the beam was the weak point.

[Cyclone03]

Bill if you don't mind,and understanding your just seeing a picture, can you give us an idea of why the broken rod would have the different colors ? I'm sure I am 100% wrong, are the gold areas marks of high heat ? I see the bright silver as spots that got hit or hammered. I also see some deep grey ( looks like iron color).  Then in the center of the rod those 3 dark spots .


Back years ago my Dad then I worked in a non ferrous foundry the workers from Mexico would heat their lunch's on the edges of the crucibles, 1350* a few inchs away will heat your tacos real well. Anyway one day somebody dropped a foil wrapped taco in the pot then "forgot" to scoop it out or tell anybody. 400lbs of aluminum was trashed along with 1/2 a day of production. The problem was found in by a machinist after heat treat,,straitening ect... a single piece of foil and taco grease. I got to see some of the parts they had small black specs inside and dimples on the surface after machining. The machinist was the first to notice the pour surface finish.     

[WConley]

Cyclone03 -

You are correct that the shiny spots are generally where hits occurred.  If the rod hadn't hit anything, you would probably see the darker color all across the fracture surface where it separated rapidly.  The gold is also in areas that got hit.  That could be material transfer from aluminum (+ heat or ??). Edit - Looks like scrape marks in those gold spots, so it probably is heat.   Hard to tell from a photo...

Edit - Gotta laugh at the tacos in the vat story!  At Ford's Essex Aluminum Plant, they had stacks of old Maytag washing machines.  The aluminum frames had just the right alloy content to sweeten the mix they were melting for cylinder heads.  The foreman would do a quick composition test of the melt, then order "Four Maytags" (or whatever number) to get the alloy just right 

[turbohunter]

Thanks for all the explanation Mr. Conley.
Really interesting stuff.
Curious what Crower would have to say.

[WConley]

No need for formality guys!  I don't feel that old and stuffy.  Just about to turn fifty in a couple of weeks 

Things like this cause my inner nerd to come out.  Most of the time I'm busting my knuckles in the machine shop, or trying to fix crappy designs on a CAD workstation.

Bill is just fine 

[Barry_R]

Those "beach marks" sure are one of the "best" images I have seen for quite a while to illustrate a fatigue failure caused by some sort of flaw.  Really sorry to see that - even though they pretty much exonerate you from any fault in the engine's demise.

As Bill noted - you can usually follow the marks to the epicenter of the failure.  It might just be an artifact of the photo - but in the second image it appears that there might be a couple suspicious rounded spots just inboard of the surface near the failure centerpoint.  The piece just starts breaking open in small sections as cycles accumulate until the remaining cross section is no longer capable of supporting the load.  Then it separates.

My engine assembly guy - Marc - might be able to add some commentary since his job description involved the lab work of breaking expensive things at Howmet and American Axle for a while.

[Qikbbstang]

How about a time frame guys?  I'd been wondering IF Jay could have been correct on his LOL "Mother's Intuition"  and actually heard something starting of the impending carnage when he was concerned about the noise just prior to leaving for Drag Week when he was going to have it aligned. Ironically when you consider she blew on the very, repeat VERY first run - that says for sure there was less then one 1/4 mile run since Jay heard the noises.  Did all those "beach marks" and other indicators happen in only 2-3 seconds of WOT on the fatal run or is it more likely Jay showed up at Drag Week with a Race Horse that already had a bullet in it?..................
    Have to say I'm confused on the fatigue being checked for by Magnafluxing and X-Ray "inspections". Sure I can understand a spec of debris within or inclusion that the "inspections" likely may catch. I think of the "paper clip" example given. Are you actually telling me you bend the Paper-Clip one time and it has a degree of fatigue, you bend it five times and obviously it now has five-times more degrees of fatigue, but at that point is there anything in Magnafluxing and X-Ray  that will say yes this Paper Clip has more fatigue then a brand new part?......... What I'm saying is I'd believe there could be a hell of a lot of "paper clip bends" before Magnafluxing and X-Ray can tell the difference between a brand new clip and a clip that has been flexed nearly to the point of fatigue that initiates failure. Those suggesting "using" the remaining "tested in combat rods" after they have been Magnafluxed and X-Ray'd is hard to comprehend.
   As mentioned "the" one rod may have died from defect/fatigue but the brothers and sisters are likely very similar and dam well came from the exact same source. Remember a AA/FD only turns the crank over about 250 times or less on an entire 1/4 mile run.

I found it amusing that Carrillo under HP Ratings says essentially nothing
http://www.cp-carrillo.com/Tech/RodTech/tabid/76/Default.aspx#hpr

Looks like ALL Carrillo Rods are Forged and then Machined they are not simply a chunk of billet steel they CNC

"All Carrillo connecting rods are manufactured from an oversized forging resulting in the proper grainflow as well as the surface removal of any potential inclusions or surface conversions generated by the forging process. "

[WConley]

BB -

That rod fatigue failure has been going on for a long time.  A tiny crack probably started during the first couple of hard runs - back in 2009.   As the crack got bigger it grew faster, until that fateful run at DW2014. 

Fatigue happens relatively slowly, so you can catch it with regular inspections.  Magnaflux exposes even micro-cracks invisible to the naked eye, as long as they are near the surface.  You put a bright-colored magnetic powder on the surface and then subject the part to a strong magnetic field.  Even the tiniest cracks will disrupt the magnetic field, causing the powder to line up along the cracks.  This effectively "paints" the cracks (even if they are below the surface a little bit) so you can see them.  A good operator can catch a fatigue failure happening early on, before there is much danger of failure.  Yes, you could see the little cracks on a paper clip after the first bend.

Unfortunately, such non-destructive inspections are not foolproof.  The little flaw in the titanium compressor disc on that Sioux City United DC-10 went undetected for years, despite regular inspections.

[Qikbbstang]

Bill Just got a chuckle thinking about the good old Sat Night Live/Mr Bill and Toonces the Cat
https://www.youtube.com/watch?v=ywQEcv22Mdk

thanks for your perspective... It never dawned on me Jay's rod failure could go way back that far, but it makes sense ...I was just nervous about stating the "torn" up rod could have allowed new noises and Jay could have been correct with the motor concerns on bothersome noises.  The fact someone else told him the sound was header leaks kind of hurts.   I've bent the hell out of a few combination wrenches to get the correct angle and hammered them right back - Forged steel is tough, to think a high perf rod could just snap cleanly like a pretzel is very odd -  I knew better.
  I kind of disagree on a paper clip indicating via x-ray and Mag testing a simple bend/ they are plated and formed (I believe) certainly not plated after forming -- think about a valve spring that may go through hundreds of millions of cycles.  One of my customers makes industrial steel cable and I've witnessed the testing/ destructive testing -- wonder how often they test rods?

[blykins]

Certainly a temporary wrench in the works, but it will give you nothing but experience.  And as they say, if you're building enough engines, you will have an issue from time to time.  It's statistics...

Give David Crower a call personally and shoot him the photos...

[Barry_R]

The question lies in the fact that - absent a failure initiation point - the rod would have gone many, many more cycles before failure from simple fatigue.  Once you have a stress point - be it a notch or an inclusion in the forging - you have a place that bending/stretching forces tend to focus upon, concentrating loads and accumulating fatigue stress in a single small and vulnerable area.

[My427stang]

I agree completely, after seeing the tracks, my guess is that rod had structural issues.  Do you have your notes on big end side clearance, bore concentricity and/or do you check to see if the they straight before you assemble?  Not that you missed something, that anyone else would have seen, but it'd be interesting if that one had any twist in it from earlier damage.

To the NDI guys, is there any cost effective test for the remaining rods that would allow Jay to trust them?  You mentioned mag and x-ray, does that tell him enough?  Needless to say, in an engine that costs that much and makes that much power, even a new set of 8 should be checked

[jayb]

I did check all that stuff on assembly, Ross, but didn't keep any notes on it.  If there was something a little odd, though, I think I would have caught it...