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?

 

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?

 

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.

 

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.

 

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.

 

Valve first.

 

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

 

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.

 

Valve...

 

MNN begging for attention attention.

 

You’re a retarded busy body Karen troll. Only a loser gives a flying fuck what anyone else is up to Gladys.

 

A good friend of mine had a rod fail at 8500 rpm in pretty much the exact same place as this one. Rod journal and bearing was fine, as the big end was still intact.

Being NA, there was no pressure entering the chamber to push the piston back down the bore, but the dome, chamber and valves were beat beat up pretty good. The intake valve was bent pretty bad, but didn't break.

I believe Randy's analysis is extremely plausible that the rod failed first.

 

What does it matter what broke first,It broke! And is going to cost him the same to fix it no matter what broke first.

 

How about this? Understanding what broke is the first step towards making improvements to prevent it from happening again.

 

OP ain't never built a bicycle. FACT!

 

My failure analysis says another thread fail by the OP!!!

 

Well, if you really think the valve failed first you either did not read my posts or did not understand the physics involved.

 

100% agree. There’s way too much piston damage to have happened on one stroke, and as soon as the rod broke the piston would have stopped.

This is where dumb dumb's lack of experience shows.

In this case, intake pressure would have continued to push the piston down into the crank and rod causing it to continue to beat itself to death.

DBT hasn't ever built anything, has never done any real failure analysis, etc. Doesn't know the difference between the failure in a NA engine versus FI.

 

There is no intake pressure in a NA application. There is a negative pressure drop “vacuum” created by the piston drawing the intake charge on the downstroke. The piston would have to remain connected to the crankshaft to create an intake draw. There would be no compression in the combustion chamber due to the broken valve head. If the piston was still connected to the rod with the valve being broken air would be forced back into the intake manifold when the piston is on the upstroke.

 

I don’t see anything in his post that mentions boost. I’ll take your word for it.

First step in failure analysis, gather your facts.

First I will revise one part of my "theory". After the rod broke the piston wouldn't stop because 23lbs of boost on a 4.125" piston would be equivalent to 307lbs of force that kept pushing the piston down after the rod broke.

 

There’s nothing in his thread post that mentions boost punk.
This is the info provided.

“I posted some information about my engine failure in TOBT but I wanted to start a thread in the Tech Section that was focused on the failure analysis.

Engine details - 4.125" bore, 3.40" stroke SBF (363ci). Rods are Oliver "Standard Light" (5.400" length) rated at 1300hp. CP pistons are used. Cam is pretty mild, hydraulic with 242deg duration and around .587/576" lift on intake/exhaust. Springs are PAC Beehives with 216lb on seat and 455lb open.

“It appears to me the Oliver rod broke first. The piston first hit #7 intake valve and knocked the head off which was laying almost intact in the cylinder. The broken rod beat against the bottom of the block's cylinder walls and knock some sections out of that. At some point the camshaft sprocket's dowel pin, ARP retaining bolt AND chain broke while the engine was still running and the other cylinders have bent valves. I believe those components driving the camshaft broke when some of the broken rod debris got wedged between the cam and the block temporarily jamming it.

Someone has suggested that the head of the intake valve may have broken first. That caused the rod to fail when the piston came up and the broken valve head overloaded the rod when the piston came to TDC and the valve head acted as a "stop". This caused the rod to fail in compression.

I'm not convinced of what happened first but the intake valve stem missing because the valve's broken head is "stuck" close to it's normal closed position. I would think if the head broke off first, that valve stem would have gone up into the guide further than normal. In other words, if the valve head broke off the valve stem wouldn't be bent and stuck in the guide.

Anyone have any ideas/suggestions. I'd certainly like to know what happened first so I can do my best to avoid the same failure in the future.”

 

Minimum amount of movements? How about this.

First I will revise one part of my "theory". After the rod broke the piston wouldn't stop because 23lbs of boost on a 4.125" piston would be equivalent to 307lbs of force that kept pushing the piston down after the rod broke. Then as the remaining section of the rod came back up it would smack the bottom of the piston pushing it back up. This meant that if the intake broke after the rod broke it would have been have been hit multiple times with enough force to cause the dings we see in the piston top. Also, look at the combustion chamber. It had minimum damage and as I stated, shows no dramatic witness mark from the tons of force it would have seen had the valve being used as a "stop" would have caused.

Post #19 in its entirety.

You haven't even been here long enough to know what members have what for cars. Another shit talking newbie that don't know shit. Right there with DBT.

 

I used the information HE provided punk!

Still but hurt over your drilled rotor bling? 🤣🤣🤣🤣🤣🤣

 

Just from personal experience I would guess it was a valve failure first. I have had that happen several times and the damage was similar to your pictures. The engine that had a rod failure did not damage the valvetrain. There is nothing worse than a valve head breaking off at 8500 RPM. It destroys everything in the engine.

 

Perhaps you missed what I wrote in another post. The camshaft sprocket drive dowel, ARP retaining bolt AND the timing chain chain all broke before the engine stopped. Probably from a piece of the rod debris getting caught between a cam lobe and the block, I found a lobe with damage that would fit that scenario. Once the cam stopped of course some of the valves would stay open and get hit by the pistons in their respective cylinders. That accounts for the "damage" to parts of the valvetrain.

 

Because it's a forced induction engine, and the failure happened at higher RPM, in boost, it makes it much more difficult to ascertain exactly the chain of events.

I've seen valve heads break off on their own. I've seen them break from pistons hitting them.

To run the piston into the valve the valve would have to be hung open or the piston would have to be moving up at the wrong time. On the normal compression stroke the valve should be closing or closed as the piston approaches. If the rod is off and flopping around it would have had to upright itself enough to push on the remainder of the rod, or the wrist pin boss or something to that effect.

 

That valve head was being shaken in the cylinder like a ball bearing in rattle paint can. You can’t have that much damage from multiple hits of the valve head across the entire top of the piston if the piston is disconnected from the rod. If the rod let go first one or two marks on the piston from the smack that broke the valve. No more piston action.

 

There is a decent amount of good information here... if you weed through the middle school bullshit. That's why this place sucks compared to what it was 10-15 years ago...

(or 10-15 user names ago depending on who's reading this)

 

That's why I posted. Truth is, I have several contacts in the industry that I've discussed this with, I like to learn from them as much as possible. But by posting, I am trying to provide valuable information, with pictures and my analysis. As you wrote, hopefully if one weeds thru the BS, I believe there is some good information.

 

Regardless on what happened ..At this point its just opinion now...

 

I disagree. I spent a lot of time looking at the damaged parts and almost every piece tells a story. For me it's like a mechanical jigsaw puzzle where the pieces put together form a picture.

 

I been on here 16 years. You been on here little over 1 year. You have over twice the post count I have IN ONE YEAR. To me that says you're an internet shit talker. While you're on here talking shit I'm building bad ass cars.

 

Nobody cares. 😭
The more you complain the more butt hurt you are.

 

Appears to me the piston had a plenty of motion after the rod broke broke. The rod hit the underside a few hundred times. You don't think those impacts are strong enough to return the piston to the top of the bore with high velocity?!?

 

No doubt the piston went up and down many times due to the manifold pressure and crank/rod driving it back up.

 

The more I think about it the more curious I am. Even if the valve broke off first, it's odd the piston stayed together but a steel rod broke. Just my opinion, the piston should have been disintegrated before the rod broke.

 

It's what I've said from the beginning. I've seen Many valves fail, but I've never seen one break a rod. I've seen many dropped valves completely destroy the piston, and the engine finally failed after the rod knocked a hole in the bore and all the water leaked out and overheated. Rod was still there in one piece though.

 

Vinny you gonna laugh at me for this? So apparently you have a picture of a shop full of 1000 HP engines you're building all at the same time????

Online punk ass bitch that don't have shit and ain't never done shit.