Were the rod bolts still intact?

 

Yes and all bearings, including those in that intact rod big, looked good.

 

Where are all the pieces of the rod. See if the rod bent like a Z. That will tell you what broke first the valve or the rod.

 

LOL

The largest piece remaining of the middle section of the rod is about the size of my little finger. The rest were broken fragments in the oil pan.

 

What brand valves? I know Manleys like to pop the heads off if the valve guide isn't perfectly perpendicular to the seat. If the valve seat moves at all in the head or sinks on one side it will side load the head and you hit the endurance limit pretty quick.

 

Ferrea valves.

 

The piston is beat to shit, if the rod broke it Would only have a few dents, the valve broke first

 

I agree with vega.

The multiple valve marks on the top of the piston makes me believe the valve broke first. The rod had to be connected for it to make all those marks. If the rod broke the piston would have had one run at the valve and it would have been over.

 

Can you take a zoomed in pic of the valve stem still in the head. Any inclusions in the metal where it broke?

 

I'll have to try with my wife's phone later. She has a new one with the better camera.

 

I'm not discounting the theory of the valve breaking first. But then I question a few other clues.

The biggest clue to me is how bad the bottom of the piston is beat up. It's so bad the spiral locks came out on one side. I am thinking the rod broke first right below the pin since there is only a short section left there. After this happened, the remaining long end of the rod kept jack hammering the bottom of the piston as it came to TDC trying to push it up. The valves opening would have kept nudging the piston down so it could be hit again. The top of the piston has a lot of hits but the hits on the bottom of the piston are much more spectacular. And if the valve broke first, to break the rod in compression I would expect to see a very large witness mark on either the piston top and/or in the cylinder head combustion chamber. Instead the marks are multiple but nowhere near as impressive as what is on the undersize. So it's obvious that after the rod broke, the piston kept getting beat upwards yet kept coming back down in the cylinder enough to get beat again and again. Yes, eventually the intake head broke off but the piston was still being beat upwards by what was left of the rod. But the force pushing the piston back up was much less than what it would have been if the valve head broke off first and acted like a "stop". Again, if that piston/rod was still intact and hit that broken valve head, I would think the force to break that rod would have left a SPECTACULAR witness mark in both the piston and cylinder heat, not the smaller multiple hits seen.

Again, I'm not saying I'm convinced totally but I'm leaning towards the scenario I just described.

 

Not necessarily, because the energy behind the hit has more effect than anything. A connecting rod flailing around has much more weight and velocity than a valve opening, so it stands to reason that the rod would cause far more damage to the underside than the valves ever could.

I’ve taken apart a number or engines that broke timing belts, and the valves bent and in some cases broke, leaving small dents on the pistons, but often not that bad. The connecting rod is large and heavy and has way more energy behind it and is moving much faster, so I would absolutely expect it to do lots of damage.

 

How many runs did the valves have on them....??

 

Same as the rods, 480.

 

I'm following along. Could the valve had broke first, banged around and then locked that cylinder up, then breaking the rod?

 

Read my analysis. If someone can point out the problem with that analysis I'd be glad to take that into consideration.

 

dropped a valve first … everything else came next

 

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.

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I think its the pac springs I literally just had my dart LS do this luckily all i did for me was fuck up the end of the spark plug and probably dinged up the piston and head a bit as it let go after the 1/8 after i already let out.....I was told from a big engine builder PAC springs had a bunch of bad springs and that cars running them have had valvetrain failures...

Because i have roller tip stainless steel jesel rockers with MAST heads with a factory stroke only turning 7400 RPM at the shifts and mine still failed it lost a valve retainer luckily for some reason the valve didnt break off or keep falling down it is stuck

 

For everyone that thinks the valve broke first, answer a simple question.

How many TONS of force do you think it would take to break that rod?

 

The valve head likely broke off first, otherwise the many marks on the top of the pistons would not be there - the piston was pounding the valve head into the chamber over a number of engine revolutions.
The valve being incompressible is likely what cause the rod to buckle, and once it was folded up, the crank beats the bottom of the piston, then, after the rod breaks completely into 2 pieces, the remaining part of the big end which is still attached to the crank, also beats the bottom of the piston.

My opinion is that the valve failed first - look for the cause of that. - possibly the guide was sticking causing piston to valve contact, or the valve overheated and the material failed ....


MANY - approximately like trying to compress a stainless steel valve head

 

Yea I agree with Randy. If the valve did break off first there would be a huge hit from the valve in your combustion chamber. Your chamber and top of piston only have light hits in it. I would think to break a rod in compression the valve would be imbedded into the piston like .5inch deep.

 

Here’s an experiment for you. Grab a scrap forged piston, mount it in a vice, and hit it with a hammer. See how much force it requires to make a dent “a half inch deep”.

Aluminum is softer than steel, but some of you seem to think it’s soft like lead apparently.

You seem to forget, with the valve head broken off, the piston will only squeeze it into the head at near the top of the cylinder, where piston speed has slowed down substantially.. the actual pinch point might only be a handful of degrees of crankshaft rotation on each pass. We’re not talking about the piston encountering pushback halfway down the cylinder when piston speed is at it’s fastest. It’s right near the top, and just for a handful of degrees of crankshaft rotation.. but it’s still a lot of stress on the rod, that is cumulative over dozens of such passes.. each hit stresses the rod and pushes it that much closer to failure. You’re thinking in terms of the rod failing the first time it hits the valve. You should be thinking about the fact that it was probably stressed over 50+ cycles of pinching that valve between piston and head. Each cycle it got weaker, until it failed.

Think about the opposite scenario - rod breaks first, piston is now free to move.. do you actually, really believe the rod flailing around is going to drive that piston all the way up to the top of the cylinder with enough force to not only just happen to time it perfectly to hit ONLY the open intake valve and NOT the exhaust, but do it enough times to break off the valve? The piston was forced back up the cylinder by the flailing rod and just happened to hit the intake valve ONLY at just the right time, multiple times to break the valve off, then continued to travel up and down the cylinder 50+ more times with enough force to create dents? That’s an absurdly unrealistic scenario that is simply not believable.

 

There is no BIG witness mark in the combustion chamber to have caused the rod to fail in compression. Thousands of pounds of force pushing the valve into the head and piston is NOT present. The valve head broke off after.

 

You obviously have not seen many catastrophic engine failures. This is textbook dropped valve damage on top of the piston. How on earth do you think the valve is going to hit the piston and combustion chamber dozens of times and hard enough to leave dents with a broken connecting rod? That is purely nonsensical.

 

There are like maybe 20-30 hit marks. If the valve broke at say 7000RPM then the piston is moving up and down. 116 times per second. Your theory doesn't add up. Plus the top of that piston has barely any damage. I have ran pistons with more damage. That is not anywhere near the damage you see when a valve head comes off.

 

After looking at the pictures again this morning. The piston head does not have the damage i thought it did. When I first looked at the picture, I thought there was holes through the piston. I beleive the rod broke first (changing my previous opinion). The boost pressure held the broken rod and the piston together (hence the minimal damage and witness marks), the centrifugal force of the broken rod pushed the piston into the valve brakeing it. That cylinder is now a pneumatic piston being pushed up with the remnants of the rod and back down with boost pressure every crank revolution, not following the cam events.
The question about the force to compression break that rod? Would not guess a number, but it would be large. I think that is plausible but unlikely. Rods do fail on the compression stroke as you know.
How many passes on those rods?

be safe, schick

 

After looking at the pictures again this morning. The piston head does not have the damage i thought it did. When I first looked at the picture, I thought there was holes through the piston. I beleive the rod broke first (changing my previous opinion). The boost pressure held the broken rod and the piston together (hence the minimal damage and witness marks), the centrifugal force of the broken rod pushed the piston into the valve brakeing it. That cylinder is now a pneumatic piston being pushed up with the remnants of the rod and back down with boost pressure every crank revolution, not following the cam events.
The question about the force to compression break that rod? Would not guess a number, but it would be large. I think that is plausible but unlikely. Rods do fail on the compression stroke as you know.
How many passes on those rods?

be safe, schick

480 runs and 30k street miles. I was running those rods right at their HP rating - 1300hp.

When we discussed this with Callies while inquiring about their rods (1500hp rating), they were surprised they lasted 480 runs. So in the future I will have to be more conservative on the number of runs at this level even with their rods.

 

Where those Oliver Speedway rods?

 

IMO, Randy's thought that the rod broke at the small end first is probably the most plausible. The valve probably broke from the piston stalling at the top of the cylinder after the rod broke, hitting the opening intake valve, causing it to break. After looking at all the pics, there's just not enough damage to the top of the piston, compression chamber or cylinder walls to make me think the valve broke first, not like the extensive damage under the piston.

 

They are called "Ford Small Block Standard Light 302 Windsor".
5.400 length and rated to 1300hp.

Ford Small Block Standard Light 302 Windsor | Oliver Racing Parts

oliverracingparts.com

 

So Callies is saying that was a lot of runs on the rods, what were they suggesting in terms of capping the runs?

 

Didn't get that specific in the conversation but they suggested at the power level I run the rods should be inspected at more frequent intervals including checking for change in length. Honestly, without a very precise jig I don't know how someone could check for a "change in length".

 

How then do you explain dozens of distinct hard hits on the piston and combustion chamber that could only be caused by the broken valve being pinched between the two dozens of times? Look closely and you can see clearly just from the pictures that some of the marks obviously line up. A close up analysis in person would surely make it even more obvious. That doesn’t happen dozens of times without the piston going up and down dozens of times with the broken valve bouncing around loose inside the cylinder as the piston repeatedly goes up and down.

You can see the very obvious witness marks from piston to valve contact on other cylinders, yet there are NO such marks in the valve reliefs on the piston that actually broke the valve. Ask yourself, if the piston hit the valve hard enough to break it, why didn’t it even disturb the carbon, let alone leave big divots like we see on other pistons?

It is impossible to conclude that the rod broke first. Simply impossible. NO piston to valve contact in the intake valve relief on the cylinder that dropped the valve. Look at it with your own eyes. The damage on the piston is everywhere but where you’d expect to see it.

 

How then do you explain dozens of distinct hard hits on the piston and combustion chamber that could only be caused by the broken valve being pinched between the two dozens of times? Look closely and you can see clearly just from the pictures that some of the marks obviously line up. A close up analysis in person would surely make it even more obvious. That doesn’t happen dozens of times without the piston going up and down dozens of times with the broken valve bouncing around loose inside the cylinder as the piston repeatedly goes up and down.

You can see the very obvious witness marks from piston to valve contact on other cylinders, yet there are NO such marks in the valve reliefs on the piston that actually broke the valve. Ask yourself, if the piston hit the valve hard enough to break it, why didn’t it even disturb the carbon, let alone leave big divots like we see on other pistons?

It is impossible to conclude that the rod broke first. Simply impossible. NO piston to valve contact in the intake valve relief on the cylinder that dropped the valve. Look at it with your own eyes. The damage on the piston is everywhere but where you’d expect to see it.

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I thought it was quite clear in my explanation that the piston WAS going up and down many times before it finally stopped. If you look at the picture below, the side of the relief has a couple of hard hits from the valve. I took the head of the valve, placed it in the relief and it matched those marks. I'm sure what happened was after the rod broke, the piston was pushed up but was either cocked in the bore or could rock enough enough for the head of the valve to hit the side of the relief where those witness marks are. After the rod first broke and the camshaft was still turning, the piston being driven up into both the exhaust and the intake valves while the were open. The exhaust valve WAS hit (it's bent) but there is NO witness mark on either valve relief because the piston wasn't hitting with the same force it hits if the rod was intact. The force of the piston coming up after the rod broke was still enough to break the intake valve (without a doubt it hit the valve several times) and bend the exhaust valve.

The engine was turning at 6500rpm when the failure occurred. That means in 1 second the crank made 108 revolutions and drove the big end of the rod up into the piston each time until enough of the rod's big end broke off and could no longer reach the piston. That 's why the piston ended up down in the cylinder. It kept getting pushed down and pushed up until the big end stopped hitting it.

Once the camshaft stopped turning, the other valves that hit the other pistons were hit by a piston still being driven by their intact rod. So yes, they had very distinct witness marks that actually dug into the piston material. But being attached to a still intact rod, the forces were much higher than the "loose" piston being thrown up into the open valves and the piston could cock/rock in the bore.

If this doesn't explain it clearly to you than nothing will.

And despite your claim, it is possible to conclude the rod broke first. ALL of the damage follows the scenario explained in my analysis.

 

I kindve feel the rod broke first and that's why it didn't beat the valve into the head, by that I mean the valve is still round and not smashed and stuck in the head like I see with most other valve problems

Either way sorry it let go but it was good to see you at drag week especially after having your hips done good luck with getting it all back together

 

Around 9:1 or 10:1? How far in the hole was the piston at assembly? I think that's playing into the difficulty in diagnosis. There is significant light damage to the face of that piston; the valve head made a lot of light contact, as it had more room than it would with high compression. I think the valve head broke free, bounced around, and fatigued the rod until the small end broke. The broken end of the broken rod could strike the bottom of the piston repeatedly. All in a matter of seconds. My 5 beer diagnosis ha ha. What I learned...replace springs and valves around 400 passes. Sorry that happened. You have to admit, you got a lot out of the engine before it let go.

 

Valve,piston,rod. What's the strongest piece in that mix? I'd think if the valve broke first,there would be a lot more damage to the top of the piston and the chamber IF that is what broke the rod. There's a lot more damage to the bottom of the piston.

Rod first IMO,but just a peasant here, no king.

 

Valve,piston,rod. What's the strongest piece in that mix? I'd think if the valve broke first,there would be a lot more damage to the top of the piston and the chamber IF that is what broke the rod. There's a lot more damage to the bottom of the piston.

Rod first IMO,but just a peasant here, no king.

If the piston hit the valve first, causing it to break, why is there no half moon witness mark on the piston inside the valve relief in the position it would be in of that hard contact had taken place? That exact kind of witness mark exists on at least one of the other pistons, but it does not exist on the piston where the valve actually broke.

That MUST be explained, as it is impossible for a piston to hit a valve hard enough to break it off and have it NOT leave a corresponding mark where the valve would have smacked it inside the valve relief. The only marks we see on the pummeled piston are everywhere else on the piston except where it would be had the piston made first contact before it broke.

Undamaged piston shows obvious piston to valve contact in the expected location if the piston hit an intact valve. Read that again and look at the picture again. There is OBVIOUS piston to valve contact with an intact valve on the largely undamaged piston. Now, look at the badly damaged piston in the exact same place and it shows NO such witness mark from piston to valve contact with an intact valve. NO witness mark from piston to valve contact with an intact valve on the beat up piston. How on earth do you explain that if the valve broke only AFTER being hit by a piston? You can see it clear as day:

 

Firstly sorry for your loss. I think the rod broke first. I run the same heads & block. I broke a rod on cyl #1 & my #7 intake valve head broke off & went through the thick dome on a heavy use nitrous piston in another cylinder without braking that rod. I have been trying to find the pictures.

 

Yeah, if the valve broke first the interaction between the broken valve head, piston and cylinder head would be dramatic to break the steel rod.

 

The marks/damage to the piston top is all over the place because it was no longer connected to a rod,unlike the other pistons.