Really? A rod defect? Not that the bearing spun, heated the rod, and broke it. The heat marks all over the big end suggest this. The black parts that came out of it would make me bank on spun bearing from detonation or lack of oil pressure.

 

Exactly!

 

Definitely looks like a spun bearing first which caused the carnage. How do the other bearings look? If the rest of the bearings are worn pretty bad then it most likely was an oiling problem, if the other bearings look fine then it's most likely an assembly error. I've been a technician at a dealership for 6 years now and every time something like this goes wrong it almost always leads to improper assembly, whether you'll be able to prove it or not is another story.

 

E75, a conservative tune, and a factory ECU don't make a good recipe for detonation. I see no signs of that, not in the cc, not on the piston crown, not anywhere.

A generalized oiling issue tends to starve #4 first, simply because that cylinder is the last one fed by the main gallery. That #1 failed alone tends to dissuade me from jumping into the oiling issue theory, unless there is ample evidence of that elsewhere in the engine.

Spinning a bearing to the extent that this type of damage results is usually indicated by at least some period of plainly audible knocking.

It seems the top of the rod and piston remain intact within the cylinder, so I see no reason to believe the cause of failure lies in that area.

That leaves the two most likely causes, those being a failure of the fasteners, or the rod itself (large end or beam). The ARP2000 fasteners are absolutely reliable when properly loaded. Over or under torquing them invites havoc. As for the spontaneous failure of an inexpensive (Chinese) H-beam rod, this wouldn't be the first time we've seen it, and won't be the last.

Photos of the disassembly may reveal more.

 

Its kind of hard to audibly hear rod knock while your going full bore down the drag strip/road coarse. The fact that the rod has heat marks on the big end, the rod cap, and everything else tells me that it spun a bearing and because of that the rod broke. It was either an oiling issue or an installed error that caused the bearing to spin.

 

90zcrex, we ran out of time to pull the rest of the motor apart, will call mechanic and ask him to pull the other 3 bigend caps off to see the bearing condition. thanks for the tip.

Ted B, thanks for your insight mate hoepfully when we fully strip the motor will get a better idea of what happened, will post up more autopsy pics when I get a chance.

 

Bean4g63, I'm also thinking it could of been bearing clearances, 1 bit of extra information I forgot to mention was my mechanic originally torqued the rod bolts up, when I found that out I asked him if he could redo them and use the stretch method and he did them to around 0.0060 which required approx 60-65 ft lbs of torque to achieve the desired stretch using ARP lube. I'm guessing this might of closed up the gap??

 

My point is, there is effectively no audible rod knock if the rod lets go almost instantly.


It's worth my repeating again that ARP2000 fasteners are absolutely reliable when properly loaded. If what you've said above is accurate, I believe those particular cap screws may have been significantly overtorqued, as I the torque preload to achieve 75% yield strength for ARP2000 3/8" cap screws is generally around ~40 ft/lb. If so, that would explain everything. Please look into it.

 

any pics of the crank journal?

 

n2oiroc: Forgot to take picture of journal, but it was BLACK as well. Will drop past mechanic this week and take some more pictures and will also remove the other 3 rods and pistons out of the block.

 

did the failed cylinder have more thrust wear than the others?

also, if the bolts failed and caused this, why would that create all kinds of heat? do you know what the rod bearing clearance was set to?

 

If the bolts are overtorqued, they will yield (stretch) first, then fail. If the engine is under load and at rpm, this will take place in a matter of seconds.

 

sounds like he over stretched them with the torque wrench then went ahead and figured it would be ok to get away with doing it by stretch gauge.

problem is, if he already over stretched them past their yield point they are trash.

also, arp lube is the last thing id be using on rod bolts based on all the information ive read on other forums about its accuracy. Id recommend loctite heavy duty anti seize for future build.

its easy to read a stretch gauge wrong also if its not perfectly center on the dimple on the rod bolt or properly preloaded.

 

TSCOMP: thanks for the info mate, will advise mechanic to use loctite next time, so far between yours and Ted B info it looks like he over torque/stretched the rod bolts... now preparing my shotgun and pay a visit to him lol

 

If your stretching the bolt how would you overshoot? I watch the gauge as I turn the wrench and stop after the needle reaches the target. Unless your not reading the dial right, why would you keep torquing?

I think it's interesting that both rod bolts snapped how they did, right above the threads and that the little end broke too. The chamber dont look that bad for the carnage underneath. What'd the piston look like? Ringlands?