fostytou

iTrader: (15)

Car is a '08 OBP GSR W/ SSS - tuned on e85 at the time with these mods:
Ghetto Intake, AMS UICP/LICP, Rexpeed O2 elim, Mil.Spec 100Cell Cat, Buschur billet cat-back, FIC 1100cc HiZ, Blaqops w/ Walboro 255, GM 3-Port BCS, Billet Al Gas Pedal


So, 8 months ago I had a motor failure. It was late at night, cold (more than usual), and I went from 50% throttle to WOT twice in 2nd and 3rd gear. The tach dropped to 0 and I smelled oil. The next day I saw oil in the cylinder closest to the trans and assumed the worst.

Months later, I finally got a chance to get under the car and check out what the problem was. To my surprise, the rod was hanging right out of the oil pan:



When I pulled the oil pan off I found the complete, clean looking wrist-pin as well as the wrist-pin side of the rod looking crushed, but crushed in like it had hit the cylinder wall / casing while spinning around. The bearing on that side was completely in-tact. One of the rod bolts had the head pulled off, and the other had pulled its threads out of the rod. Looking at the bottom of the piston it appeared it was slightly turned (more on that later). I assumed the rod bolts had given way after the rod had hit the block since the bottom of the cylinder and edge of the block was beat into a bloody pulp. The tach had gone to 0 because the rod had sheered most of the teeth off of the crank angle sensor on its way out.

I tried to place a long screwdriver on top of the piston and hit it with a hammer, but the piston didn't seem to want to move anywhere. At this point I assumed I had put a hole in the cylinder wall (possibly thanks to my tuning, possibly thanks to excessive boost due to cold), lodged the piston in that hole, and ripped the wrist-pin relief off of the bottom when the crank continued to pull the rod down. I assumed this because although I could not see a hole, it was strange that the piston was rotated and I thought it was "stuck" in a hole since it would not move down in the cylinder.

------ Fast forward a couple of months

Tonight I finally got some time to finish pulling the motor and getting the head off. To my surprise the piston was actually turned >90* in the cylinder:



...but even more surprising was the fact that it popped right out the top with very little effort and the cylinder walls were almost completely clean in any of the piston's movement area:




At this point I'm wondering what caused the failure. Unfortunately my full-time logger decided to stop logging *1 day* before this... extremely frustrating. I'm not sure how the rod could have pulled away the bottom of the piston like that. I would think detonation could crack the top of the piston or cause some failure there, but without the piston being "stuck" somewhere I'm not sure how the bottom could just fall out like this.

I welcome any theories. My most reasonable thought is some twisting related to the rod bolts right now since I'm going back to the drawing board, however it appears the top of the rod hit the block and cylinder walls many times before breaking off so I would think that disproves that theory.



High res copies of any photos will be here (next to a smaller copy): http://thefrost.net/randomfiles/rand...0111101.Motor/


I can try to snap more pics of the rod / carnage on request if you can think of anything specific.

murlo26

iTrader: (9)

Woa, I haven't seen one fail like this yet. Very interesting. I'd still bet your rod bent and/or broke and led to this. The rods are almost always what I see go, especially on close to 400wtq cars like yours. But this still looks very strange.

I wonder if the Rod did the whole "s" shape deal and somehow broke the botttom of the piston. I still am confused how it flipped though lol.

fostytou

iTrader: (15)

The flip was just a convenient location to set it upside down (for anyone who that wasn't obvious to).

I guess i should grab some better pictures of the rod later. From my recollection it looked pretty damn straight. My friend's that were broken looked more like a C shape.

David Buschur

iTrader: (53)

It is hard to say if the pin boss failed first or if the rod could have failed and then the piston/pin area. I'd guess the piston failed first but who knows. I've seen this in a few EVOX engines.

murlo26

iTrader: (9)

Whoops, I am noob lol. Where was the piston when you found it? I still haven't had enough caffeine today I guess.

fostytou

iTrader: (15)

Thanks David. In your experience would you say that a specific stress caused that or just a design flaw / weakness?

Piston was sitting in the top of the cylinder just hanging out. Didn't seem to want to go down, but popped up very easily. I guess that might have been due to the rings since they were hanging out a little bit.

PRS

iTrader: (2)

The factory rods and pistons aren't strong enough, unfortunately its a weak point in the design. There obviously could be other factors.

fostytou

iTrader: (15)

Any elaboration other than that? Gates ran 11,000 track miles at 560whp and this ran 15,000 at less than 400, though possibly too much boost the tune / boost was probably a factor here. The question is why did the bottom of the piston get ripped out if there was no cylinder wall damage?

scheides

iTrader: (10)

Holy fahk! So is either the block or crank still any good? Head ok?

STi2EvoX

Ouch.

fostytou

iTrader: (15)

Block is beat to hell at the bottom of the cylinder from the rod hitting it so many times. The cylinder walls in that cylinder has a bunch of tiny pock marks from debris. There are 2 small vents in the block, 1 right below the cylinder facing forward and another right above the crank angle sensor.

I'll post the comedic picture of how I held the rotating assembly and a few pictures of the rod shortly.

evofan_08

iTrader: (16)

Mrt performance says that the rods break at to high a boost level, they didn't disclose at what boost level but after hearing that I immediately turned my boost waaay down.

Evofreak21

iTrader: (2)

Was this on the stock turbo? What were you tuned for boost wise?

fostytou

iTrader: (15)

Holding the rotating assembly to get the crank pulley bolt off :


Rod images. Looks like there was a bit of a twist at the head but I can't tell if that was pre or post impacting the cylinder wall many times. You can clearly see that the rod bolt that didn't shear is shifted southeast (in the picture):












As always, full size images are in the link above.

fostytou

iTrader: (15)

Stock turbo. I was 28-30psi boost wise at peak (depending on weather/etc) so possibly a bit high, but the failure probably happened near 5,500 RPM, so it was probably lower... although the cold may have kept it up there. I'm not sure if being at 50% throttle then going WOT had put the boost correction up and lead to an overboost when it got to WOT.