Balance shaft pics? Does it still rotate?

The BS assembly was fine, untouched, and rotates. No chipped teeth on either gears.

So... in the Quest for knowledge... we forge onward. This is a piece of rod I found in the oil pan.... and i've placed it where it seems to best fit.

Wow! Hmmmm, Thats one theory that may be laid to rest.

Been studying you pics with a local engine builder who specializes in race engines only, not regular rebuilds (albeit he has never touched a DI motor, and dosen't care to) he thinks all the oil "may" have entered the IM when the piston went sideways.
He also said that without looking at all your parts in person it's just speculation!
He has lots of broken rods laying around and the twisting, shear, and snaping of yours is leading him to think off center force against piston/rotating assembly. He suggests checking all the other rods for any signs of twist/bend with the proper measuring equipment. (not eying)

I will say this. Any metal fatigues over time. If the extra power run on an engine is above the failure threshold at some time in its life, it will fail - it is essentially a ticking time bomb. This failure threshold follows an S-N curve similar to the one below

http://cal.vet.upenn.edu/projects/sa...er_13/13F2.jpg

As you can see, the part will fail at a much lower stress as it is cycled more and more. The rod should be designed such that stock load should be below the lower point of the curve as it ages (or at least for the warranty period). This failure is due to microcracks forming and expanding over time weakening the beam.

However, the odd car that is never driven hard (or is stock) that bends rods is just a mystery because that is compressive overload (or twisting force) that shouldn't happen at a few psi. The BS is probably not locking but excessive crank endplay and clutch being pushed in under load, stuck injector, oil in combustion chamber, preignition are all possible culprits.

To learn more, read this: http://www.forging.org/FIERF/pdf/FatigueBehavior.pdf

Well, I remembered tonight... that way back on the "fateful" day, I picked up some pieces that were on the back of the flat bed... after we got my car off. One of those pieces was the missing chunk of connecting rod.... yes it managed to get out of the block... and the engine bay, and rattled it's way onto the tow truck's bed.

Great documentation!

Lex, excessive endplay is exactly what my local builder ask about!
Seems like a lot of people are popping while shifting!?
Again, just spectulation though!
Wouldn't that explain the twist of the rod causing abnormal stress and early failure, as you posted above?

What are the black dots on the fracture surface here? Are those impurities embedded into the rod?

http://www.mazdaspeedforums.org/foru...mbly-endon.jpg

thats funny we just went over testing metal in my engineering class tonight

Hahaha, lex i was just gonna ask you if you saw any manufacturing flaws in the rod, but you managed to beat me to it. We'll see if that is indeed some sort of flawed inclusion.

Staple gun kid, your kicking ass, i just want to thank you a ton for documenting this so damn well. Your helping us all out man, and imo we owe you. When you are done with your diagnostic stuff, you should at least send the rod with possible flaw to lex, and maybe more pieces. But til then, keep snapping away!

Man, in a strange way I almost HOPE the rods are flawed. And we have proof. What a huge victory that would be over those fuckers. No wonder they are so tight lipped about these engine failures.

It would be interesting to know how high the temperature gets in the engine/combustion champer in these cars? I mean to high temperatures eventually weakeness the rod and such.. just speculating.. :)

Sorry, I think it's the angle of the photo. Those are just smoothed areas, due to an impact on the surface. Not black impurities.

are the stock pistons and rods cast?

i thought i read somewhere that they are forged, but i dunno.

rods are forged, pistons aren't.

heres a theory posted by many from day1. The rods are weak, mystery over. Why is everyone still digging for a reason why these things blow? Name any mazda engine with strong rods.....

Well now that you solved that mystery can you please start working on the no big power one please lol.

http://us1.webpublications.com.au/st...9/2921_7lo.jpg

i dont even know what engine you posted.

well isn't just only that, theories ...

im glad their is someone out there trying to confirm what causes these engine to blow.

BPC8

Well ive waited to post to this tread, it seems to me that the piston seems to have cracked before the rod failed as evidensed by 3 of the 4 cylinders being dry and only one being wet with oil.

I am also going to bet that the pin boss area failed first and the piston stayed together until the other side slowly cracked, this is evidenced by the cracks in the crown around the boss that did not fail, the engine noise and imbalance in the weeks before, and the burning oil in the days prior to total failure.

I dont see anything that indicates that it was a heat related failure since nothing is blue, melted, or scored and the piston has no coking on the underside. I also dont see anything that indicates that the pin siezed in the boss or that it contacted the cylinder wall due to a lock type failure.

I see no obvious signs of major detonation on the piston crown since the top ring area seems to be intact.

I think it was a straight up material failure, here is a paragraph about the hypereutectic pistons that we have that I ripped from a piston mfg web site:

Modern pistons are made from a variety of aluminum alloys and are produced using two basic processes. Most OEM pistons are made from alloys which contain a large percentage of silicon and are produced by a casting process. These high silicon alloys are known as "hypereutectic" alloys due to the silicon levels above 12%. A properly designed and manufactured cast hypereutectic piston offers excellent durability, light weight, and relatively low cost. However, these alloys are brittle and thus not very tolerant of detonation. High quality forged pistons are made from alloys such as 2618. These have a much lower silicon content (<1%)and this makes them less prone to cracking under extreme conditions. In addition, the forging process itself tends to produce a tougher piston.

Nice work with all the pics. :headbang:

It's crazy looking at these pics because it seems to be an exact clone of my rod and piston from my motor blowing up... only I had a LOT of the pieces exit the block and sit on the splash gaurd under the engine. Also... the cylindar where the rod snapped was dry but the other 3 were filled with oil on top of the pistons...And I blew while shifting...with FFS... On a good note though I got the warranty to go through and should have my car back Monday or Tuesday!!!

Piston cracking first was my first thought as well. The remaining skirt is so beat up that I also saw the rod breaking first and free spinning and breaking/cracking the piston at the bottom of the bore, finally pushing it up, as another possibility. Especially since there are no real signs of detonation on the piston surface.

It could be that the piston cracked which caused the rod to eventually fail due to the uneven loading, once the rod failed it smacked the piston a few times and pushed it up the bore.

I really dont think that crack in the piston crown was cause by anything other than the piston itself failing.

I took some shots of each cylinder, for comparison reasons.

Looks pretty normal to me.

LOL if this is the case.

"hi i'm mazda, spec ^these^ pistons and now lets develop a tune that constantly pushes our cars into detonation for minimum emissions. good bye"

I just wanted to ask a quick noob what could cause an engine to blow up question.

We brought up the topic before about how un-even flow in the IM or ports could cause un-even cylinder filling, and potential for lean cylinders and heating etc, but that hasn't been confirmed or denied.

Another question in my mind though, arising from the same scenario but not heat or afr related, is could the uneven cylinder filling cause an un-even loading on the crank from some cylinders exerting more power than others?

Interesting that I read this right after a post about MA Performance pnp intake mani.... They reduced the flow variance in the cylinders from around 26% to 5%... Not saying it's gonna be a magic cure for motors blowing but I can't help but wonder if the uneven air flow is part of the problem...

All located pieces of rod and piston have been packaged up and sent West to Lex. So that he can analyze them in his secret lab.

Here's a shot of the spark plug from #1 (the wet one), and some other plug (the normal one)

Is it just the pic or is the strap on the blown plug eaten away/smooth near the tip?

looks the same , look at the electrode in a str8 up line in relationship with the ground strap on both. prolly a lighting issue

I want to come back to scuffing of the bore. The cylinder that failed had the most scuffing on the exhaust side. The intake sideskirt broke off the piston when it failed. This is leading me to believe the ring locked in the bore with the piston going up. That put pressure on the intake sideskirt and on the exhaust side ring which broke along with the rod.

Can you tell me how the bore feels in the highligted area? Do you feel scuffing marks (does your fingernail catch on them?)

Grab a non broken piston ring and place it in the bore and push it down to the scuffing point. See if the ring lies flat touching the bore evenly or if there are any gaps forming between the bore and the piston ring in places indicating a bore that is not true. It may not be visible to the eye but worth a shot.

Also, I know this is a shot in the dark, but feel the bore all the way around from intake to exhaust where it is highlighted. Do you feel the bore being completely even and round?

Thanks again!

Pics for Lex.

Sorry to be asking for so much, but is it possible to get the other rod bearings? I am seeing some wear on the edge of these bearings that seems odd.

Bearings from rods 3 and 4. The large scratch in #3 was sustained during handling.

the pauter rods are insanely beefy

Here's a couple (not so great) shots of the wrist pin end bearing. Not nearly as photogenic as his bigger brothers.

This is from rod #4