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Old 07-06-2008, 12:51 AM   #1
benw
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Default broken valve, catastrophic failure, with pics

Hi there. Here's the result of my last trip to the circuit for high speed touring. On the 5th session of the day, I was rounding the final corner onto the main straight, when the engine let go. As I shifted from 3rd-4th, I lost all power, the engine stopped, and a magnificent spy-hunter smoke screen filled my rearview. Pulled the plugs and #2 was smashed beyond recognition and the others were saturated with oil. Oil was also found throughout the intake tract.

Car is a stage 2 STI, conservatively tuned on 91 octane but was running straight 104 unleaded all day. The new forged build gets underway next week!




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Old 07-06-2008, 12:57 AM   #2
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What is the round circular piece on the bottom of the last pic?
Thats a really cool looking logo!

But wow, savage failure!
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Old 07-06-2008, 01:05 AM   #3
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Quote:
Originally Posted by moosecakes View Post
What is the round circular piece on the bottom of the last pic?
Thats a really cool looking logo!

But wow, savage failure!
the head of the valve that broke off!
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Old 07-06-2008, 01:07 AM   #4
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But where did that little picture on that peice come from?
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Old 07-06-2008, 01:13 AM   #5
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that looks awesome I will try and do that much damage to mine nice I love destruction
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Old 07-06-2008, 01:47 AM   #6
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you know you did good when the ring is off the piston. wait, where is the piston?
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Old 07-06-2008, 02:23 AM   #7
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Quote:
Originally Posted by n2oiroc View Post
you know you did good when the ring is off the piston. wait, where is the piston?
when we rotated the engine on the stand, it sounded like someone turned a gumball machine upside down. so to answer your question, it might be more appropriate to ask "where ISNT the piston?"
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Old 07-06-2008, 02:46 AM   #8
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Quote:
Originally Posted by benw View Post
when we rotated the engine on the stand, it sounded like someone turned a gumball machine upside down. so to answer your question, it might be more appropriate to ask "where ISNT the piston?"
at least the piston pin stayed in place.
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Old 07-06-2008, 09:08 AM   #9
kevinh211
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wow! that is a catastrophic failure. you should be proud of yourself!
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Old 07-06-2008, 09:59 AM   #10
St.race
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What do you think could cause it? You do not think it's a bad front O2 sensor?
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Old 07-06-2008, 11:26 AM   #11
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Ouch - sorry to see it go like that. Good luck with the new build though.
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Old 07-06-2008, 11:38 AM   #12
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Well the fact that it was tuned for 91 and running 104 could be part of it.. when running high octane fuel it will lean out you mixture. When I was still running my fp green I did the same thing and the car had sereral problems, once 92 was used again the probs went away...
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Old 07-06-2008, 01:53 PM   #13
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Quote:
Originally Posted by Sinister redlines View Post
Well the fact that it was tuned for 91 and running 104 could be part of it.. when running high octane fuel it will lean out you mixture. When I was still running my fp green I did the same thing and the car had sereral problems, once 92 was used again the probs went away...
I have never experienced High Octane fuel leaning out a mixture, I've experienced quite the opposite. High octane gas like C16 for example has a higher specific gravity that regular 93 octane and usually results in a richer mixture.
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Old 07-06-2008, 02:18 PM   #14
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100% true, actually its not "richer", it burns more completely with a higher igniting temperature and a lower combustion temperature (theres actually scientific terms for it) but all and higher octane on a low octane tune with "technically" make your a/f's rich, that is why you can tune 12-12.5-1 on 110 leaded...

Anyway thats some freakish carnage, well done on destroying it in a sweet way, sorry to hear it though! GL with your new build.

Btw, by the looks of things, it looks like you kissed the intake valve, bending the stem, causing it to tear into your guide. That would explain why the valve broke and why there is damage in your intake port, away from larger chunks.

I'm probably wrong though..
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Old 07-06-2008, 02:27 PM   #15
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you guys are smart! yes, the fuel was probably to blame. I was running very conservative ignition timing and overfueling, in an attempt to prevent engine damage (talk about backfiring in your face). I guess this caused the combustion event to occur much later, even into the exhaust stroke, which could toast the exhaust valve.

Quote:
Originally Posted by JSarv
Btw, by the looks of things, it looks like you kissed the intake valve, bending the stem, causing it to tear into your guide. That would explain why the valve broke and why there is damage in your intake port, away from larger chunks.
Intake ports are all fine. It appears to have snapped off and fell into the #2 jug where it went bonkers.

I am waiting for some of the built motor "pros" to arrive to chime in, though!
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Old 07-06-2008, 02:37 PM   #16
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I had the same thing happen to my vw golf back a few years ago. Looking at the valve damage as well it being down. Check the tension on the springs. As some spring manufactures are not as good as they claim. If that is the cause kick there butt.
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Old 07-06-2008, 03:47 PM   #17
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My opinion is that the piston broke first not the valve. I've seen valves break before and usually they get stuck into the port or piston and you don't see this type of damage. Also the guide is broken so the valve had to hit something and bend, the head didn't just pop off. Did you stop as soon as you knew something was wrong and get towed in or did you drive it back to the pits?

The other thing I see is it looks like the piston was hitting the head on the intake side. The impression is strong enough that you can see it after the other damage so I'd guess it was hitting pretty good.
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Old 07-06-2008, 04:30 PM   #18
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Quote:
Originally Posted by gumby647 View Post
My opinion is that the piston broke first not the valve. I've seen valves break before and usually they get stuck into the port or piston and you don't see this type of damage. Also the guide is broken so the valve had to hit something and bend, the head didn't just pop off. Did you stop as soon as you knew something was wrong and get towed in or did you drive it back to the pits?

The other thing I see is it looks like the piston was hitting the head on the intake side. The impression is strong enough that you can see it after the other damage so I'd guess it was hitting pretty good.
+1. I am no professional, but I bet the piston cracked earlier in the run. A piece finally was dislodged, came off (ringland) and moved to the top of the piston where the valve tried to open to. I suppose it could have gotten between the valve and the head, but either way it weakened the valve shaft, put it off-center and when it tried to close, popped off. I am guessing this was at high rpm there is so much damage. I believe this because there are so many depressions from being hit by little fragments of metal in the head and a majority of them are around the broken valve.
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Old 07-06-2008, 04:37 PM   #19
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Quote:
Originally Posted by gumby647 View Post
My opinion is that the piston broke first not the valve...
Probably, but a rod bearing could've let go, causing the initial and subsequent hits as well. Either way, the carnage is just as complete.

BTW, those big chunks? There's your piston, at least part of it.
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Old 07-06-2008, 09:05 PM   #20
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Honestly that looks incredibly hard to diagnos. I know for a fact for a short period of time your valve was running bent, maybe even just one duration, but it was bent and tried closing.

I honestly doubt your fuel was the ultimate cause. It could have been a number of things including oil starvation (which seems to be likely) it could have been a fuel starvation, causing a catastrophic detonation or hell it could have been a million things, but I really don't think it was due to over fueling.

It really looks like your valve closed several times while bent, but that could have also been the valve or piston chunk getting tossed around.


I love seeing carnage pictures like this (hate for it to happen) but I had a Civic VX for a DD and hit 1st instead of 3rd getting on the freeway and bent EVERY single valve and drove it 3 miles back home with 2 valve riding on the piston (made about 3hp, over the 85hp stock, but it ran...) Never actually broke a valve just dropped 2 retainers. Anyway the point is, it sucks, but it goes to show how badly things can get in a real quick way.


again good luck... Get a tune for the higher octane next time, its well worth the power and longevity.
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Old 07-06-2008, 10:48 PM   #21
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It's hard to judge an overheated exhaust valve on these engines since they just use sodium-filled stainless valves, not inconel/nimonic. The types of temperatures which destroy the high-end valve materials usually also turn the exhaust piping a white-ish color, due to excessive oxide formation, IIRC.

Standard stainless can be overheated at pretty low exhaust temperatures, even sodium-filled, if the thermal flux becomes too much for the conductive mechanisms to remove before the next exhaust stroke. (which means higher exhaust gas density even at the same temperature can be enough to do it under certain conditions)
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Old 07-06-2008, 11:11 PM   #22
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Interesting...but what are you saying happened?
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Old 07-06-2008, 11:34 PM   #23
benw
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thanks for the theories, I appreciate it!

some facts:
- occurred at the track, 10-turns, 1.8 mile road course
- track temp was 90+
- oil temps were high. 125-130C
- oil used was fresh german castrol 0w-30

ECU map details:
- AFR was 11:0 tapering to 10.6 at 6500 (shift point)
- ignition advance was 11 degrees rising to 22 at 7000
- I never had this map knock a single time on 91 octane, it's my super conservative daily map.

As soon as the failure occurred, the engine shut down and stopped. A total of about 1/2 a second. The car was running great right up until the event, I never had any indicators or anything.

Tonight I got my donor block split and taken apart. It has a perfect crank and rods, and the bores look great. I will be doing CP 99.5mm pistons, CP rings, ACL bearings, and Eagle rods, and am considering some Brian Crower stainless valves for the new heads I've got.
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Old 07-07-2008, 04:53 AM   #24
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A dropped valve has nothing to do with fuel used.

There are two common ways to drop a valve.
A valve breaks off when the valve stem fatigue cracks, usually due to the engine being slightly over rev'd bad enough to float the valves and very slightly bend that valve.

After that each time the valve closes, the valve stem bends slightly as the valve springs and combustion pressures force the valve head back in full contact with the head/valve seat. Eventually that continuous bending will work harden the valve stem and it will break.

Been there done that.

It can also happen if a valve spring breaks, or it tosses a keeper and drops the valve down into the chamber while the engine is running.


A lean out might have burned a valve or melted a piston but it would be very unlikely for it to cause a valve failure all by itself.


If you can still see the fracture line on the valve stem, and it looks like a beach with high water marks on it, that is a sure sign it was a fatigue failure. If you have pieces of valve spring in the valve cover or munched cams/retainers and buckets, I would bet on a broken valve spring or tossed keeper (and or a major over rev sometime prior to the failure).

It is very common for this sort of failure to happen on throttle lift entering a corner or on a shift.

That said the way that piston came apart makes me think the piston broke/siezed in the bore, possibly when a ring butted due to insuffecient ring end gap, and yanked the top of the piston off at the ring groove. If the valve breaks first the valve head usually slices and dices the piston crown up into little pieces and the piston tries to push the valve head out through one or more valve ports, frequently dishing the crap out of one or more valves as they almost get stuffed through the valve seat. I see there are very few if any clear impressions of the valve head hitting the head edge on, which would be numerous in my experience if the valve head came off first. When my 401 V8 sucked a valve it dropped the entire piston down into the pan in very small pieces, as the valve head cookie cuttered the piston crown and turned it into confetti. In my failure it was a tossed keeper caused by the outer valve spring breaking. If the ring siezed in the bore you might be able find a clear vertical score down the cylinder wall not aligned with the wrist pin ends, or an obvious "bite mark" where the ring dug into the wall just as it yanked the piston crown off at the ring groove/wrist pin hole.

Larry

Last edited by hotrod; 07-07-2008 at 05:11 AM.
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Old 07-07-2008, 11:04 AM   #25
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have you checked to see if the valve stem is still in the guide? if not, check for it on the teardown.
It (or the lack of clearance for thermal expansion) could be the cause of the failure and I'd also be sure to maganflux or trash those cams.
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