Broke connecting rod?

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swampbuggy
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Re: Broke connecting rod?

Post by swampbuggy » Wed Sep 19, 2018 8:37 pm

Brian, what you described in the above replies exactly what happens on every exhaust stroke pretty much. Mark H.

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Re: Broke connecting rod?

Post by Newold1 » Wed Sep 19, 2018 9:18 pm

What Brian is trying to describe is that form of tensile loading on the rod. It's the opposite of compressive loading on the rod. Happens every time the piston changes direction and is pulled back down when the crank is changing the direction of the piston and it starts traveling back down in the bore.

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Re: Broke connecting rod?

Post by MadBill » Wed Sep 19, 2018 9:40 pm

On the power stroke at WOT, there is several hundred psi cylinder pressure assisting to decelerate the piston in the vicinity of TDC, whereas on the exhaust it's only a few psi and on closed throttle it can be up to ~12 negative, adding slightly to the rod tensile loading.
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Re: Broke connecting rod?

Post by lance flake » Wed Sep 19, 2018 9:56 pm

Kevin Johnson wrote:
Wed Sep 19, 2018 5:49 pm
It is possible that the bluing seen in the collection photograph is an optical illusion ?? But you appear to see it as well.

https://www.efatigue.com/training/Chapter_3.pdf

When you bend a paperclip wire back and forth it generates heat in the area of plastic deformation. Eventually failure ensues. If the rod was accidentally dropped or struck and a small unnoticed nick was created that would be a stress raiser. There could also have been an invisible internal flaw in that area.

Send the pieces to be looked at by a trained metallurgical engineer.
Yea the pic had a shadow in it. I had to go back and look at the rod to be sure it wasn’t discolored

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Re: Broke connecting rod?

Post by lance flake » Wed Sep 19, 2018 9:59 pm

kosky racing wrote:
Wed Sep 19, 2018 7:03 pm
What parts were carried over on the three engines that broke? -Ignition- fuel- manifold?
Yes those 3 things, ati balancer, and comp belt drive. Nothing else not even head studs!

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Re: Broke connecting rod?

Post by lance flake » Wed Sep 19, 2018 11:51 pm

Newold1 wrote:
Wed Sep 19, 2018 7:16 am
I am not thinking it was a hydraulic situation based on some broken rods I have seen over the years. Usually in a hydraulic cylinder situation there is some bending movement laterally or horizontally in the rod beam and there is usually some bearing compression marking. That rod broke and pretty much stayed in a straight vertical shape other than the tearing and beating it took during and after seperation.

Put the pin on a piece of glass or a super flat surface and roll it to look for a bend. If the cylinder hydrauliced the PIN WILL BE BENT!
The wrist pin is out of round about .003-.0035.

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Re: Broke connecting rod?

Post by digger » Thu Sep 20, 2018 1:12 am

Kevin Johnson wrote:
Wed Sep 19, 2018 5:49 pm
It is possible that the bluing seen in the collection photograph is an optical illusion ?? But you appear to see it as well.

https://www.efatigue.com/training/Chapter_3.pdf

When you bend a paperclip wire back and forth it generates heat in the area of plastic deformation. Eventually failure ensues. If the rod was accidentally dropped or struck and a small unnoticed nick was created that would be a stress raiser. There could also have been an invisible internal flaw in that area.

Send the pieces to be looked at by a trained metallurgical engineer.
There a difference between things getting a bit warm to the touch and going blue

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Re: Broke connecting rod?

Post by Kevin Johnson » Thu Sep 20, 2018 7:21 am

digger wrote:
Thu Sep 20, 2018 1:12 am
Kevin Johnson wrote:
Wed Sep 19, 2018 5:49 pm
...
When you bend a paperclip wire back and forth it generates heat in the area of plastic deformation. Eventually failure ensues. If the rod was accidentally dropped or struck and a small unnoticed nick was created that would be a stress raiser. There could also have been an invisible internal flaw in that area.

Send the pieces to be looked at by a trained metallurgical engineer.
There a difference between things getting a bit warm to the touch and going blue
That is correct but failure analysis involves analyzing empirical data. The scientist or engineer should not discount physical evidence simply because it seems unlikely to her or him. In modern times that is akin to "if we cannot model it then it must not exist." When bluing of the metal surface was mentioned the person in possession of the item explicitly confirmed the presence of the bluing and even offered an alternate theory for its presence.

There are many resources to see the typical physical progression of a fatigue crack (beach marks, for example) and a college course chapter was provided. The bluing seen radiated from a locus as would be expected from a stress raiser.

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Re: Broke connecting rod?

Post by kosky racing » Thu Sep 20, 2018 8:26 am

With the wrist pin being bent -firing at the wrong time took place-is this a crank trigger-was the wire from the trigger near a plug wire?

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Re: Broke connecting rod?

Post by digger » Thu Sep 20, 2018 8:56 am

Kevin Johnson wrote:
Thu Sep 20, 2018 7:21 am
digger wrote:
Thu Sep 20, 2018 1:12 am
Kevin Johnson wrote:
Wed Sep 19, 2018 5:49 pm
...
When you bend a paperclip wire back and forth it generates heat in the area of plastic deformation. Eventually failure ensues. If the rod was accidentally dropped or struck and a small unnoticed nick was created that would be a stress raiser. There could also have been an invisible internal flaw in that area.

Send the pieces to be looked at by a trained metallurgical engineer.
There a difference between things getting a bit warm to the touch and going blue

That is correct but failure analysis involves analyzing empirical data. The scientist or engineer should not discount physical evidence simply because it seems unlikely to her or him. In modern times that is akin to "if we cannot model it then it must not exist." When bluing of the metal surface was mentioned the person in possession of the item explicitly confirmed the presence of the bluing and even offered an alternate theory for its presence.

There are many resources to see the typical physical progression of a fatigue crack (beach marks, for example) and a college course chapter was provided. The bluing seen radiated from a locus as would be expected from a stress raiser.
It's not going to get hot enough to go blue

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Re: Broke connecting rod?

Post by canada1 » Thu Sep 20, 2018 10:26 am

What does the piston skirt look like?
What does the cylinder bore look like?

Piston seizing in the bore? Just a thought I had.

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Re: Broke connecting rod?

Post by lance flake » Thu Sep 20, 2018 12:20 pm

Kevin Johnson wrote:
Thu Sep 20, 2018 7:21 am
digger wrote:
Thu Sep 20, 2018 1:12 am
Kevin Johnson wrote:
Wed Sep 19, 2018 5:49 pm
...
When you bend a paperclip wire back and forth it generates heat in the area of plastic deformation. Eventually failure ensues. If the rod was accidentally dropped or struck and a small unnoticed nick was created that would be a stress raiser. There could also have been an invisible internal flaw in that area.

Send the pieces to be looked at by a trained metallurgical engineer.
There a difference between things getting a bit warm to the touch and going blue
That is correct but failure analysis involves analyzing empirical data. The scientist or engineer should not discount physical evidence simply because it seems unlikely to her or him. In modern times that is akin to "if we cannot model it then it must not exist." When bluing of the metal surface was mentioned the person in possession of the item explicitly confirmed the presence of the bluing and even offered an alternate theory for its presence.

There are many resources to see the typical physical progression of a fatigue crack (beach marks, for example) and a college course chapter was provided. The bluing seen radiated from a locus as would be expected from a stress raiser.
I could see the shadow you were talking about in the pic. I had to go back and look at the rod with my own eyes to make sure there was no blueing of the rod. Does the pics I posted last night give you the answer you were looking for about the blue mark?

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Re: Broke connecting rod?

Post by lance flake » Thu Sep 20, 2018 12:21 pm

canada1 wrote:
Thu Sep 20, 2018 10:26 am
What does the piston skirt look like?
What does the cylinder bore look like?

Piston seizing in the bore? Just a thought I had.
No sign of seizure

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Re: Broke connecting rod?

Post by Kevin Johnson » Thu Sep 20, 2018 1:28 pm

digger wrote:
Thu Sep 20, 2018 8:56 am
Kevin Johnson wrote:
Thu Sep 20, 2018 7:21 am
digger wrote:
Thu Sep 20, 2018 1:12 am


There a difference between things getting a bit warm to the touch and going blue

That is correct but failure analysis involves analyzing empirical data. The scientist or engineer should not discount physical evidence simply because it seems unlikely to her or him. In modern times that is akin to "if we cannot model it then it must not exist." When bluing of the metal surface was mentioned the person in possession of the item explicitly confirmed the presence of the bluing and even offered an alternate theory for its presence.

There are many resources to see the typical physical progression of a fatigue crack (beach marks, for example) and a college course chapter was provided. The bluing seen radiated from a locus as would be expected from a stress raiser.
It's not going to get hot enough to go blue

Rods are commonly blued in service. Here is a SpeedTalk discussion about it from five years ago:
https://www.speedtalk.com/forum/viewtopic.php?t=37469

This occurs despite all sorts of oil droplets flying around in the crankcase landing on the rod surface, so, an amazingly similar environment --- all that is required is the loss of the hydrodynamic wedge and constant flow of oil to reject heat from the bearings. In a fatigue crack being cycled likely well over two hundred times a second (twice the RPS) it is very easy for localized galling of projections/asperities to occur. This generates heat just like failing bearings generate heat.

This is beside the point that if a fait accompli exists with bluing then it is the responsibility of the scientist/engineer/technician to accept that empirical evidence.

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Re: Broke connecting rod?

Post by Kevin Johnson » Thu Sep 20, 2018 1:36 pm

lance flake wrote:
Thu Sep 20, 2018 12:20 pm
I could see the shadow you were talking about in the pic. I had to go back and look at the rod with my own eyes to make sure there was no blueing of the rod. Does the pics I posted last night give you the answer you were looking for about the blue mark?
I will certainly accept that your subsequent inspection showed no bluing.

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