1 breaks loose. Rod spinning around hammers the other one til it blows too.

 

It's trash. I bet the crank is tweaked, and the heads have bad mojo.

If he reuses ONE part, and it grenades, he will wonder what if ..............

 

Assuming a piston broke free that would throw a hell of an imbalance on that section of the crank. This is a stroker engine which has minimal clearance between the rod cap bolts and the block. It would be interesting to see if there is evidence of them striking the block. As tough as a crank looks, if it has an imbalance it will flex significantly. And if it hits resonance that will amplify it. Now as this occurred on acceleration that gives an excellent chance of hitting an RPM that matches the resonance frequency somewhere along the curve. A disclaimer here, I don't know what the resonance frequency is on a crank and maybe the engineers have designed them to keep the resonance frequency well above normal operating RPM's so this continues to be supposition. But even without resonance, the base vibration could be enough to have started a catastrophic chain of events. Consider that at 6000 RPM the pistons are cycling more than 30 times per second. If one piston is gone the the imbalance could be enough to cause the other to overextend on its stroke. It may be a testament to the engine that it held together long enough to destroy the second piston.

 

I felt the piston discussion issue was important enough to start a new thread... this thread got kind of bogged-down....

https://www.corvetteforum.com/forums...endations.html

 

I added more pictures to the first post

See below for replies, thanks all for chipping in! The shop will revise the heads and inspect the crank in January. They will also check out the camshaft.
Their first reaction to the bearings were: bad for the 5K mileage, but not worn yet.

The motor was built in two stages. Bottom end was done by a professional shop in my country. I was not present during the build-up, but them not using callipers and micrometers would highly surprise me.

They:
- clearanced the block,
- zero decked it (with my fel-pro gaskets I came exactly at 0.040 compressed thickness for 'ideal' quench),
- bored it 0.030 over using torque plates and, of course,
- also honed it,
- installed the crank for me (as I did and do not have the proper tools (or knowledge/experience ) to do so myself),
- installed the camshaft bearings and,
- connected the rods to the pistons.

They also did some work on the heads: cc-ed them and made sure the spring pressure was equal.

The second part was my own:
- Installed pistons rings (checked gap)
- Installed pistons
- Installed cam
- Installed oil pump (melling HV) + checked pan-pickup clearance
- Freeze plugs, and all the rest of the engine

What is interesting is that several of the other pistons have either a piece of the skirt chipped off or a crack in the side. I'll take your advice into considering should I build another engine.

I think this is where the nitrating process helped. It's a strong cam, however that probably did not prevent it from bending a bit. This is yet to be determined though.

Local shop says bearings were not looking good for the mileage but not bad enough to be the most likely cause. Crank shows some discoloring which could be a sign of either oiling/cooling issues at some point in time.

I expect this to be the case.

Definitely...

I hope I have better karma, but that is one of my considerations in the course to follow. Same goes for the affordable LSx swap: if I buy used and that one has issues, then I will probably beat myself up for not building a new engine.

For now the re-use list is: carb, intake, ignition, rockers, lifters, timing chain and gear.

Oil pump unsure; probably needs a very thorough cleaning and of oiling was an issue...

Oilpan (hamburgers' with baffles and windage tray) ... probably trash too.

Thanks! Very interesting read

 

New cam, new lifters. You don't want those.

 

Since you have more info now, it would be interesting to the group to come to a final conclusion on the cause of failure. The presence of two missing pistons, and several others with cracked skirts certainly sounds like that could be the primary failure point. Especially since the valves were intact. However did you have any of the contributing issues to hyper piston failure?
As in:
Sounds like you had 9.5 compression.
How hard did you rev it?
What Octane gas? 87 or 92 or ?
Were all the rod bolt big-ends still attached to the crank?
Ever have any detonation / pinging? At full or part throttle?
You mentioned E85. Is that recent? Did you have the carb re-tuned for it?
Any idea on the spark / distributor timing curve? Stock timing or more aggressive?
I don't remember seeing any camshaft specs?
Personally I am curious as to whether the 15% ethanol in the E85 had anything to do with it. It should burn hotter, leaner and faster, and get worse MPG. I'm suspicious of the hotter and leaner tendency may have over-stressed your pistons, if you ran it hard.
If the E-fuel you mentioned is E-85, the entire fuel system needs to be modified, including the carb:
https://www.hotrod.com/articles/conv...or-the-street/

 

A piston came apart and the rest of the carnage was after that. I think it would be a good bet that detonation killed this engine.

 

"One of the first things taught in introductory statistics textbooks is that correlation is not causation. It is also one of the first things forgotten."
-Thomas Sowell

"Most of you have heard the maxim correlation does not imply causation."
-Nate Silver

 

"The Patriot"
Militia Corporal Gabriel Martin: [After colonial militia killed some redcoats who had their hands raised] Those men were about to surrender!
French Major Jean Villeneuve: Perhaps. We will never know.

If it is assumed the first thing to break was a piston, the next question is why did it break? Detonation - maybe. Another possibility would be latent defect which weakened some part of the piston and which had been propagating each time a cycle above some threshold stress caused more damage until sudden rupture. Detonation could have accelerated that. But I doubt there is any way of telling without thousands spent in forensic analysis of whatever is left and then trying to recreate the failure. The real question is as the OP is really interested in, how to avoid this in the next engine. Lower the power or get higher quality and stronger parts (or a mix of both). No guarantee in there since even the best quality parts can have a defect. But if they are inherently stronger (forged pistons vs. cast) the additional strength can be more tolerant of defects at a given stress level.

Another quote - Gilligan's Island:
Country girl next door Mary Anne: Money can't buy happiness
Millionaire's wife Mrs. Howell: Nonsense darling, you're just not shopping in the right places

In general, I'm with Mary Ann (or wish I was - but I digress

But conditionally, on this one I side with Mrs. Howell. If happiness is being 99.9999% certain that when you put the pedal to the floor nothing is going to break despite going from 0 to 60 in 4 seconds, then more money is the only thing that can buy that.

And the last quote:
"The right stuff"
Gus Grissom : "No Bucks, No Buck Rogers"

 

money can't buy happiness, but a lack thereof will buy a whole bunch of misery. as vince said. it looks like a piston failure. I bought a set f 8 forged OEM pistons to get 1 good one for my 454 boat engine. 6 were covered with detonation holes. actually burns small hole in piston with each ping. they were ugly. I threw them out. but they would have held up if I installed them. spend the money on the best pistons and get them correctly fitted. and make sure ignition is set up correctly. small blocks don't like more than 34 degrees mech without vacuum figured in. 46 with vac.

 

SBC don't like more than 34* mech total? Huh? What? Does Lars know this?
And 46* w/ Vac? What? Huh?

Do I have to do mine all over again? I thought I was good to go at 36 / 52.

I bet you were running a whole lot more than 36* with your detonation issues. Likely from a faulty timing light or incorrect timing tab or a slipped harmonic balancer.

 

I think it was revised down in his latest paper. Something about modern gasoline and flame propagation.

 

Sorry for the late reply. Holidays...

Calculations say around 10.5, 10.6 static compression with 5cc flattops (2 valve reliefs), zero deck and 0.040 compressed thickness head gaskets.

Kick-down and well over 100 mph with a TH350 3 speed and 26" inch tire diameter... at least 4500 - 5000 rpm

Dutch gas is not quite the same. I usually fill up with "Euro 98" which is 98 RON. This particular day I had no choice but to fill up with "Euro 95" which is 95 RON. Only since October all fuels have 5% bio-ethanol added due to European environmental legislation.

Yes.

Not that I know of. Hard to say with sidepipes perhaps.

E5; 5% bio-ethanol added.

More aggressive per Lars' paper for peak performance; different springs, weights and vacuum thingaminga.

CompCams XE274H: http://www.compcams.com/v002/Pages/389/XE274H-10.aspx

I think it's a case of overstress too. Possibly in combination with a lack of oil or cooling, Did have a 7qt oil pan (Hamburgers with baffles and windage tray) and a Melling HV pump. Running Valvoline 5w50 VR-1 racing oil.

 

Quote: " This particular day I had no choice but to fill up with "Euro 95" which is 95 RON." "Ever have any detonation / pinging? At full or part throttle? "Not that I know of. Hard to say with sidepipes perhaps."
There's your problem.
Too much compression and too low of Otcane. And aggressive timing. And too much cylinder pressure. And you couldn't hear it ping. You had detonation and didn't even know it. And Cast Hypereuetic pistons don't like detonation.
With your recent 10.6 Compression Ratio, Next time I'd suggest a CR below 10, like 9.9 with a cam like that, and Forged Pistons, and a little less aggressive spark curve.And still the best gas.An even lower CR like 9.5 if you want to run the cheap gas. Then it should run well for decades.
With that cam and 10.6 CR you had 8.6 Dynamic CR and that would require the best street gas, and a careful timing curve. Unfortunately that day it got neither.
FYI: I ran almost that exact same compression in my 70 LT1, only with a 10 degree more aggressive cam that helped kill some cylinder pressure. I raced it hard and tuned it for 25 years. It ran it's best on 98 Octane (93 blended with 5 gal race gas). To run it on street 91-93 Octane (your 98RON) I had to detune the timing some 8 degrees initial, and total and limit the vacuum. Or I got bad part and full throttle detonation, especially coming off light throttle cruise mode. The timing changes were not ideal for power, they pulled 30HP out of it. I had it setup so I could change the timing in 2-3 minutes to suit the "gas mix of the day". I eventually got tired of the Race Gas mixture and just left it in the detuned mode.

You had the same setup, but without the timing detune, and then a tank of even lower 95RON (our 87 Octane) was just too much for it.

So sorry for your loss. But at least you know how to build the next one so it won't happen again.

 

To OP:
Was looking at pistons (not yours) and remembered something which caused me to think of your engine failure.
A great many pistons have an "offset wrist pin."
Pistons with offset wrist pins available without regard to cast, hypereutectic, forged, material choice.
Depending on orientation, this offset can be used to mitigate slap/noise or to reduce stresses on skirt.

? I ask, do your pistons have offset wrist pins ?

 

Thanks all for taking the time to read through my post and putting in your thoughts, opinions and knowledge to help me assessing my engine failure!

Though not completely certain I can conclude a combination of circumstances and the way I built my engine have led to this happening.

Now I will need to decide on which direction to head into next. For that I will first draw out a few possible routes and then get back here.

Keywords: 383 SBC GEN1 vs. Big Block vs. EFI vs. LQ4/LQ9/LY6/LSx

 

No, these were not offset. You can check Jegs for specs they still offer the same Eagle 383 kit I used.

 

efi bbc?

 

< = 500 Gross HP engine? 383 GEN 1 with EFI or carb.

>500 Gross HP LS3