[DeepBrainThrombosis]

Referring to this thread here:

https://www.yellowbullet.com/threads/failure-analysis.2703478/?post_id=74688893&nested_view=1&sortby=oldest#post-74688893

I post this not to pound my chest, but for legitimate educational purposes.. we can all benefit from understanding failures like this.

Do you think the valve snapped off first, or the connecting rod broke first? Study all his pictures and think it through. Which failure happened first? Vote and then explain your reasoning here. Let’s all learn together.

 

[Jrsfox87]

looks like piston hit the valve went to shit and out the door

 

[DeepBrainThrombosis]

looks like piston hit the valve went to shit and out the door

That doesn’t answer the question of which broke first - the valve, or the connecting rod?

 

[68468]

Valve broke first.

That doesn’t answer the question of which broke first - the valve, or the connecting rod?

Valve broke first.

 

[Jrsfox87]

That doesn’t answer the question of which broke first - the valve, or the connecting rod?

well if the piston hit the valve common sense would say oh so the valve broke something u lack

 

[DeepBrainThrombosis]

well if the piston hit the valve common sense would say oh so the valve broke something u lack

I don’t even know what to say to this.. you’re both very right and very wrong in the same post. That’s.. an achievement of sorts.

 

[Warp Speed]

I've witnessed a bunch of dropped valves over the years, but I can't remember ever seeing one break a steel rod....?

 

[GARYB69Z]

Ive broken a valve before and only damage was on the top of the piston and comb. chamber..I doubt that could break the con rod.

 

[DeepBrainThrombosis]

I've witnessed a bunch of dropped valves over the years, but I can't remember ever seeing one break a steel rod....?

But if the rod broke first, how do you explain the dozens of dents in the piston and combustion chamber from the piston being jammed into the head with the broken off valve pinched in between? And no witness marks from the valve contacting the piston where it would have in the valve relief has the piston broken it off?

 

[DeepBrainThrombosis]

Ive broken a valve before and only damage was on the top of the piston and comb. chamber..I doubt that could break the con rod.

I took apart a 6.4L Hemi years ago that broke off one of it’s sodium filled exhaust valves, destroyed the piston and snapped the connecting rod. Very much the same as this engine. I don’t think dropping a valve means guaranteed connecting rod failure, but like the OP says, his rods already had a ton of passes on them, more so than the manufacturer recommends. So it was very likely already weakened to some extent.

What cannot be explained, if the rod broke first, is the extensive damage to the piston and combustion chamber from the piston repeatedly pinching the broken off valve between the piston and head. And yet, NO witness marks where the valve actually would have contacted the piston had the piston hit the valve and caused it to break off.

I would bet that if you took that engine to a real forensic professional to determine the cause of value, they would conclude the valve broken first.

 

[VinnyVette9340]

Valve snapped first. Rod had to be connected to the crank to repeatedly beat the top of the piston on multiple cycles. If the rod broke first it would have had one wack at the piston top / broken valve head squeezed in the chamber because the piston would have been disconnected from the crank and the piston would be more or less floating or jammed in position.

 

[Hollow65]

Valve snapped first. Rod had to be connected to the crank to repeatedly beat the top of the piston on multiple cycles. If the rod broke first it would have had one wack at the piston top / broken valve head squeezed in the chamber because the piston would have been disconnected from the crank and the piston would be more or less floating or jammed in position.

This. Valves are like water, they don’t compress.

 

[Topfun99]

Only an narcissistic idiot would start a poll like this. And what's funny, is him thinking that it matters what the results of the poll matter to me.

Anyone who thinks the valve dropped first is welcome to read my analysis and debate what I wrote directly in the thread. However, I think Warp Speed, perhaps the most experience engine builders on this site, made a pretty simple comment that means more than the results of a superficial poll.

 

[axel breaker earl]

Valve first.

 

[Warp Speed]

But if the rod broke first, how do you explain the dozens of dents in the piston and combustion chamber from the piston being jammed into the head with the broken off valve pinched in between?

The piston bouncing off the crank/broken rod and being sent back up into the top of the bore?

And no witness marks from the valve contacting the piston where it would have in the valve relief has the piston broken it off?

If the rod broke first, how would the piston stay aligned so the valve would hit it directly in the pocket?!?
While the top of the piston is beat to shit, you can count the strikes in the chamber........
Rod broke! Imo

 

[DeepBrainThrombosis]

The piston bouncing off the crank/broken rod and being sent back up into the top of the bore?


If the rod broke first, how would the piston stay aligned so the valve would hit it directly in the pocket?!?
While the top of the piston is beat to shit, you can count the strikes in the chamber........
Rod broke! Imo

Laughable. You could rotate that piston around in the bore and not one of the existing witness marks line up with where the intact valve would have hit it. They are all in random spots around the top of the piston. And what is imparting all this rotational force on the piston? Why do we seen damage concentrated in two spots on the bottom of the piston and not all the way around? The idea that the loose piston was actively rotating around the bore as it is magically propelled up and down 50+ times is utterly laughable. And remember, this propulsion of the loose piston up into the chamber needs to be done with precise enough timing to contact the open valve within a roughly 20° window of crank rotation in order to even make contact. So we have magical piston rotation in the bore, magical pumping up and down 50+ times, and magical timing.. it’s just laughable.

So once again, you believe that the loose piston was somehow propelled up into the chamber with enough force to break a valve off, then continue to bounce up and down the cylinder another 50+ times, somehow magically making contact with the crank at just the right time to keep this process going 50+ times? It’s just laughably absurd. Of all people, you know better.

 

[Warp Speed]

Laughable. You could rotate that piston around in the bore and not one of the existing witness marks line up with where the intact valve would have hit it. They are all in random spots around the top of the piston. And what is imparting all this rotational force on the piston? Why do we seen damage concentrated in two spots on the bottom of the piston and not all the way around? The idea that the loose piston was actively rotating around the bore as it is magically propelled up and down 50+ times is utterly laughable. And remember, this propulsion of the loose piston up into the chamber needs to be done with precise enough timing to contact the open valve within a roughly 20° window of crank rotation in order to even make contact. So we have magical piston rotation in the bore, magical pumping up and down 50+ times, and magical timing.. it’s just laughable.

So once again, you believe that the loose piston was somehow propelled up into the chamber with enough force to break a valve off, then continue to bounce up and down the cylinder another 50+ times, somehow magically making contact with the crank at just the right time to keep this process going 50+ times? It’s just laughably absurd. Of all people, you know better.

It's obvious you don’t see this type of failure much?

 

[DeepBrainThrombosis]

It's obvious you don’t see this type of failure much?

It’s obvious you aren’t capable of forensic analysis? Compare the two theories and see which one requires more precise lineup of all the holes in the swiss cheese. Make an honest judgement and there is no comparison. Valve breaking first easily explains all the damage without any holes in the cheese lining up. Rod breaking first requires precise crank to piston timing to push it up the bore at just the right time to make contact with the open valve, while retaining enough force to do so despite other forces slowing it down, while also rotating actively in the bore from some unknown force, and doing this 50+ times without any of the swiss cheese holes closing up. Which is the more complicated theory?

 

[Warp Speed]

It’s obvious you aren’t capable of forensic analysis? Compare the two theories and see which one requires more precise lineup of all the holes in the swiss cheese. Make an honest judgement and there is no comparison. Valve breaking first easily explains all the damage without any holes in the cheese lining up. Rod breaking first requires precise crank to piston timing to push it up the bore at just the right time to make contact with the open valve, while retaining enough force to do so despite other forces slowing it down, while also rotating actively in the bore from some unknown force, and doing this 50+ times without any of the swiss cheese holes closing up. Which is the more complicated theory?

😂

 

[Breadburner]

Valve...