Thanks to Clint for snapping this while he was there......

What do you experts think happened here?












Gurgen

 

Looks like detonation to me. With the pistons being damaged the way they are, that's a very likely sign. The rod likely failed from the excessive compressive loads while the crack journal was at about 90 degrees. This would place the greatest lateral load on the rods. What kind of fuel system were you running? It looks like either it leaned out badly or timing went way askew as the other rod looks like it twisted up a bit too. If it was kind of a freak thing, I would think only one piston/rod might be affected. But with at least 2, it sounds like a problem common to all the cylinders. Perhaps even the spark plugs. What heat range were they? And out of curiosity, which pistons were the rods associated with?

And wow, the heads on our motors are thick.

 

Damm Gurg... W/e happened, it doesnt look pretty lol! It looks like there was alot of detonation as mentioned already!

 

I am strongly suspecting the rod bolts.... Not sure at this point if I agree with the detonation assessment, I haven't seen it myself... It is definitely not pretty, a lot of carbon deposits. However... the engine WAS NOT detonating at the time when this happened... it could have done so before of course, which created some sort of a crack or weakness in the piston. The rod could have failed and cause a break in the piston... Also, another suspect could be the spark plugs...which had about 1000 miles on them, and they were in pretty bad shape. That's could be what caused it. Also, the carbon deposits look bad but are not abnormal (they look that bad partly because of the coolant that filled the cylinders and stayed there for 2 months). Just look at some working motor pictures with the heads off... they are pretty black...

 

Forgot to answer your question...

I was monitoring everything very closely... There was no detonation detected by the J&S (or audible), A/F was in the mid-low 11's, I was full throtte at ~4500rpm and the boost was 5.7 psi. I was taking out about 5-6 degrees of timing across the board..

Gurgen

 

hey gurgenpb, i'm just wondering, did you have a return line setup?

 

The reason I say detonation is that the ring lands are usually the first to go when that happens. Especially on cast pistons. While it is obvious the rod bolts broke, the question would be at what point. If the rod snapped, the broken rod would be flailing around at high speed. If it hits anything(the block) it's quite possible the rob bolts can easily break at this point. Looking at the cap, it looks like only one side came off at first and stretched the cap as the remaining piece of rod became detached from the crank.

As far as the carbon, it's possible your oil problems before could have been the culprit. I can't remember what specifically that problem was but I don't think it has a big bearing on this. And the plugs? Were they melted or was the insulation cracked? Very common with severe detonation.

If the rod bolts failed, I doubt you would see 2 rods bent.

 

It is easily possible that a failure in one of these safegaurds can cause the problem. If say the timing retard device failed abruptly it could easily cause a very immediate and catastrophic failure. Short of having a datalogger, something like this would be hard to catch even when monitoring it as you would have to be watching the guage as it happens and the guage would have to respond immediately. Just throwing out ideas. Either way the pistons show signs of detonation damage. I would like to hear specifically about the condition of the plugs when you took them out...

 

Wow there is a lot of carbon in there. Probably related to all the smoking you mentioned earlier.

 

If a failure originates in only one part of the rotating assembly, for whatever reason, can't that single event, as it unfolds, trigger cascading failures that radiate outward & away?

I'm thinking even though the contents of multiple cylinders were damaged, the triggering failure may have occured inside one cylinder. The resulting stresses created by the lone triggering event could have caused cascading failures elsewhere in the rotating assembly.

 

YEs I have a fuel return (short loop) fuel system with a fuel pressure regulator (rising rate).

Gurgen

 

Ckwik

The plugs were not broken of course... I would of course replaced them if this was the case. They (the rim) were just carbon-covered, and not nice and tan in color...

I concede that the detonation is an issue here as well. I am afraid that this is the price I paid for being a perpetual prototype test-mule for much too long... And the smoking issue ... I would immensely surprised if it wa only a coincidence... It has to do something with the broken piston... just like David of APS predicted...

Gurgen

 

Bullseye... you are right on... very possible

As far as the datalogger... that is exactly what I am going with now...

 

Dammit im so lost, if i go FI on any car i def. need to do ALOT more research, i thought i knew "alot" i know nothing LOL

 

yea, the last time my motor detonated to doom the piston lands cracked just like that. there also seems to be a hell of alot of stress damage to those rods, seems like a combination of things was goin on here. maybe you spun a bearing in the process casuing the rod to twist like that? look for tiny grey specks on the pistons, valves, or spark plugs as signs of detonation. the large amount of carbon deposits suggest that you were indeed running rich, but there may be a weak spot in your tuning where you may have run lean for a split second to cause detonation and crack your pistons like that. watever the cause, that is one deceased block!