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Old 01-31-2009, 06:58 PM   #1
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Default Awesome Rod Failure Carnage (dialup beware)

So I pulled the blown engine out of the car today and tore it down to investigate the engine condition after the engine failure discussed here:
https://www.miataturbo.net/forum/t29521/
This is the event preceding the engine build to be shown here:
https://www.miataturbo.net/forum/t30899/

First of all special thanks to Barry who came by with his fantastic engine hoist and gave me a hand with the engine/transmission removal/teardown. From start (engine in the car, on jack stands) to finish (torn apart engine) took less than four hours. Engine tilt attachment on the engine hoist FTW!

After tear down and accident reconstruction process, I am almost certain that this failure was caused by an overstressed rod that collapsed, and not brought on by detonation or hydrolock. This is my hypothesis on how the failure happened:
1. Cold temperatures and slight overboost created cylinder pressures too high for the rods.
2. On the power stroke the #4 piston rod buckles, twists, and collapses, greatly shortening the piston to crank distance.
3. The #4 piston travels downward and impacts the crank.
4. BANG!
5. In rapid succession the piston skirt shatters, then the piston wrist pin 'caps' fail, tearing the wrist pin completely out of the piston skirt.
6. The wrist pin and connecting rod begin flailing wildly around in the bore, smashing two holes in the block (one on each side), damaging the windage tray, and breaking the connecting rod into bits, along with several other parts.
7. The wrist pin is ejected from the engine case, along with several pieces of piston.

For complete photos of the carnage go to this link:
Picasa Web Albums - John - Engine Removal

Here are some of the key photos with descriptions below:

Last edited by ZX-Tex; 01-31-2009 at 09:07 PM.
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Old 01-31-2009, 07:01 PM   #2
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Barry contemplates the meaning of power and its consequences


Look, Daddy blew his engine! Hahaaaa!
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Old 01-31-2009, 07:07 PM   #3
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The hole clear through the block. Turns out there was another hole behind the starter that could not be seen until the starter was removed. The starter is OK and was cleared by paramedics at the scene.

Last edited by ZX-Tex; 01-31-2009 at 07:27 PM.
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Old 01-31-2009, 07:11 PM   #4
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The #4 piston stuck in the bore. Note the extreme failure of the piston wrist pin 'caps'.


All the bits and pieces of the #4 piston, wristpin, and connecting rod, gathered from all throughout the engine and engine bay. Check out the awesome bend and twist in the center section of the rod.
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Old 01-31-2009, 07:15 PM   #5
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This is what happens when the rod end is turned into a high-speed rotary hammer.


Here is where the piston hit the crankshaft. Otherwise the crank looks great. Hopefully it is reusable; I'll see what the machine shop thinks.
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Old 01-31-2009, 07:22 PM   #6
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Ugh, that gives me the chills.
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Old 01-31-2009, 07:30 PM   #7
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*Walks outside to dial down MBC*

Damn. Was the engine fully warmed up when this happened? Or was it 1/2 warmed up? Perhaps it seized a piston, which caused the rod to stretch/fatigue/fail?
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Old 01-31-2009, 07:34 PM   #8
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This is starting to sound like the old days when everyone pushed their engines and we had lots of 99+ blow-ups in the 250+ range. I think you get some god motors, but most eventually give up and exit the block!
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Old 01-31-2009, 07:38 PM   #9
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Oh yeah, I almost forgot to mention... When we were cleaning up I picked up the remaining piston/rod assemblies and noticed that another one of them is also bent! I do not know which bore it came from.



The fact that a rod other than #4 was bent (not due to a hot cylinder), the lack of any detected detonation when it happened, the lack of signs of detonation on any of the components (no chipped rings, plugs, pistons, etc) not-extremely-aggressive timing, no head gasket leaks, and good AFR, leads me to conclude that this was simply an Euler column bucking event brought on my too much boost.
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Old 01-31-2009, 07:46 PM   #10
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Quote:
Originally Posted by patsmx5 View Post
*Walks outside to dial down MBC*

Damn. Was the engine fully warmed up when this happened? Or was it 1/2 warmed up? Perhaps it seized a piston, which caused the rod to stretch/fatigue/fail?
Nope, engine was completely warmed up.
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Old 01-31-2009, 07:46 PM   #11
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Quote:
Originally Posted by [email protected] View Post
This is starting to sound like the old days when everyone pushed their engines and we had lots of 99+ blow-ups in the 250+ range. I think you get some god motors, but most eventually give up and exit the block!
I agree. I do not think there is anything sinister at work here other than my EBC tuning
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Old 01-31-2009, 07:58 PM   #12
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must be the cold winter air.
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Old 01-31-2009, 08:26 PM   #13
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Quote:
Originally Posted by y8s View Post
must be the cold winter air.
Yes I believe that also contributed; A highly knowledgeable IC Engine R&D Engineer buddy of mine suggested this as well. It was a cool morning when it happened, in the upper 40s to lower 50s IIRC. Most of us know from experience the fact that engines tend to make more power in cooler weather, all else being equal.
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Old 01-31-2009, 08:32 PM   #14
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God damn that is impressive.
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Old 01-31-2009, 08:33 PM   #15
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Holy ****
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Old 01-31-2009, 08:55 PM   #16
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I don't think I would re-use those parts.
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Old 01-31-2009, 09:11 PM   #17
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Dang it, my last hopes of saving the #4 components are dashed against the rocks. Corky I was going to see if you guys could weld that stuff back together for me. Then I could drill and ream the rod end. I thought I could also bend the rings back into shape. I also figured I could patch the holes in the block with some JB Weld and bits of sheet metal.

Corky you know this is all your fault. Your stuff works too well. I think you owe Barry and I a Margarita.

I am just glad it looks like the head was not damaged, and the crank is OK (hopefully). It could have been... worse?

Last edited by ZX-Tex; 01-31-2009 at 10:29 PM.
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Old 01-31-2009, 11:01 PM   #18
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I like how not only is the south Texas miata crew full of big-time turbo cars but also full of people who could kill me...instantly, lol.
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Old 01-31-2009, 11:04 PM   #19
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speaking of corky's stuff working too well,I met a guy at the NASA TT today with an MSM and a BEGi kit which was driven in 3-classes by 3-drivers...and its a daily driver. lol
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Old 01-31-2009, 11:22 PM   #20
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Quote:
Originally Posted by Corky Bell View Post
I don't think I would re-use those parts.
Due to Corky's experience and wisdom, I am going to concur. Do not reuse those parts.









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