catastrophic engine failure analysis

[eiuskoalman]

ok, so i know this guy whose got an 86 gn with a motor problem. seems that the crank is now broken (a 2 piece unit) and there are multiple piston skirts with damage (chips/chunks broken off). this damage did not occur with race gas or a race chip, just a simple street setup. my question to you, what type of problems usually lead up to damage like this?

 

[Intercooler]

Detonation, locking the convertor, general crank flex.

 

[S2V6RACER]

History of motor? Mileage? Mods? Need a lot more info on your problem. I have heard of cranks breaking back in the days from a problem with the damper fit(harmonics).

 

[eiuskoalman]

the motor was rebuilt and has less than 30K on it since the rebuild. it recieved a new crank (turbo correct). there were no known performance modifications made during the rebuild. the motor made good oil pressure (aprox. 20 at hot idle) and used zero oil. the car has been driven fairly aggressively on the street for the past 8,000 miles or so with NO mechanical failures. it has not seen any track time, not even a set of sticky tires. i'd assume a motor with harmonics problems would show some serious problems long before this one did, but its your opinion i'm looking for.

 

[MARINES185]

this wouldn't happen to be turbowannabe's car, would it?
I've been following the story and it seems kinda strange
on both parts. I can't believe that there wasn't no sign of
problems and this happens. I also can't believe that
turbowannabe didn't have a little fun with this car either.
the first thing i did when i got my 87 gn was a brake stand
then preceeded to see how fast i could getting going. this
was only 5 minutes after i owned the car. crank could of had
a stress crack and just finally went on poor turbowannabe.
his side of the story is that you lied to him about when it was
rebuilt and couldn't come up with paper work. Even if
turbowannabe beat the hell out of the car i can't see a
perfectly good running engine grenading like that. there
probabaly was a problem that you didn't know about.
things happen and i don't think this will be solved.

 

[eiuskoalman]

well, thats a totally different post and yes, we all have our own opinions on how a 16 year old might operate a new car. the opinions i'm looking for at this point relate to the mechanical conditions leading up to this engine failure. thanks

 

[RareT]

Sounds like some serious detonation. Running low octane gas (87) and flogging the car would cause it.

Ed

 

[azgn]

even 93 octane could do it......

 

[The Radius Kid]

From what I've seen,that kind of stuff happens when the stresses are relatively low on the crank.I've read more than once where a guy was justing accelerating onto the highway or freeway into traffic and the engine just died.Synopsis:crankshaft failure,busted in half[engine did a fair bit of high H/P racing before dieing in regular service].
Now,you say this engine was rebuilt 30,000 miles ago?Are you dead sure the same crank went back into the engine that was in there in the first place when you brought it in for a rebuild?
Could have been someone was looking for a low mileage crank for a race G/N and saw that one you had and swapped?
I don't doubt you looked after the car,but something sure smells rotten in Denmark,so to speak.

 

[clean86]

I bought my first GN in November, I bought because it had a fresh 2500 mile motor as well as some perf parts and was in very good shape. But the fresh rebuild was the kicker. After driving the car for two months getting use to it and fixing a few little things not to my likeing I was ready to go tho the track for some base line runs. On the way to the track I saw Woody going the other way. Being windy I thought the track may be closed but had to check. After seeing for my self that it was I headed home. Driving home the **** hir the fan 5 PSI OF OIL PREASURE and I had to stall the converter just to get it there. Very long story short the place who built the motor are a bunch of hacks!!! Non turbo crank, screwed up the front cover , cylinders out of round and so on. So my point is , finally, Just because it was fresh does not mean it was a pile of crap.

 

[blackbuick87]

EIUSKOALMAN, you state that the motor has 30k on it, but then you say the last 8000 miles have been all street, fairly aggressive, etc. Is it safe to assume that you only put 8k on the clock and the previous owner before you put 22k on the motor? If that is the case you have no idea what that original owner did with the car and all bets are off. Even if you took care of it perfectly the other owner could have beat the piss out of it from day one

 

[TurboDave]

I think I would still suspect the crank. Everybody involved says it was a turbo specific crank. BUT was it??? was it really? How verifiable is that info?

 

[texasturbo]

broken crank!!!!

Just my thought. Any indication the torque converter ballooned !!!! Might be kinda hard now, but what does the thrust bearing look like?????Where did the break occur????

 

[eiuskoalman]

blackbuick87, i didnt say the rebuild had 30K on it, it clearly says LESS THAN 30K. i'm not trying to be a smarta$$ but just making generalizations. and yes, the 8,000 miles represent those that i'm responsible for.

 

[Grumpy]

hmmmm how about a random victem SOB....**it happeneds.....Melissa's Limited T broke a crank while I was drivin it....just gettin on the highway an the car stalled....towed home an found the "2 piece crank"....motor had 189k an 700 -11 sec runs on it....then we had a 10k TTA have a crank failer....it is a used 15 year old car ....

 

[blackbuick87]

OK, so you really have no idea how many miles are on the rebuild, or its more than 8k and less than 30k? I am not trying to start anything either, just trying to make the point that someone other than you drove the car a significant number of miles and you have no idea how it was driven

 

[eiuskoalman]

ok, ok, lets put a number here for ya blackbuick. lets just say that the previous owner put 15K on the rebuilds, hypothetically speaking that is. i know that person and also know his driving habits. the motor was babied after the rebuilds because he couldn't afford to do it again. sure there were times he leaned into it but it wasnt abused like so many cars out there.