Carnage........Whats your take?
- Thread starter jdpolzin
- Start date
- Joined
- May 28, 2001
Balancer broke, crank went into a "speed wobble"?? The rest is history. I'm betting this didn't happen "just driving along".
Broken balancers are not uncommon. Bal loose, then cracked, knocked timing out of whack??
Broken balancers are not uncommon. Bal loose, then cracked, knocked timing out of whack??
Sorry for you luck, that sucks.
Here’s my guess
It's hard to see from the pictures, but it looks like there are striations from a crack forming in the crank between the 3rd main bearing and before #5. Striations form when a crack grows; the smaller the striations the longer the crack was growing. If they are truly striations, then this is likely a crack plane and the point of failure.
Once cracked then the rear piece of the crank was cantilevered. At high engine speed the crank would highly loaded (probably the rear main bearing will be torn up the worst) , the load, in addition to transferring torque from the front piece of the crank angled the rear piece of the crank. This angle would and put load on the wrist pins evenually ovalizing the wrist pin bores. Then the wrist pin pulled out from the piston, I noticed that #6 rod is similarly bent and I bet that that wrist pin is on its way out too. Once the wrist pin on #5 was free, it was free to smash into the crankcase which busted it out. All of this probably happened instantaneously.
The harmonic balancer damage was resultant and not causitive.
This is eerily similar to a crank I had fracture a few years back that I use as a paperweight right now.
Here’s my guess
It's hard to see from the pictures, but it looks like there are striations from a crack forming in the crank between the 3rd main bearing and before #5. Striations form when a crack grows; the smaller the striations the longer the crack was growing. If they are truly striations, then this is likely a crack plane and the point of failure.
Once cracked then the rear piece of the crank was cantilevered. At high engine speed the crank would highly loaded (probably the rear main bearing will be torn up the worst) , the load, in addition to transferring torque from the front piece of the crank angled the rear piece of the crank. This angle would and put load on the wrist pins evenually ovalizing the wrist pin bores. Then the wrist pin pulled out from the piston, I noticed that #6 rod is similarly bent and I bet that that wrist pin is on its way out too. Once the wrist pin on #5 was free, it was free to smash into the crankcase which busted it out. All of this probably happened instantaneously.
The harmonic balancer damage was resultant and not causitive.
This is eerily similar to a crank I had fracture a few years back that I use as a paperweight right now.
Car was a 484 block, .030 hypers, file fit rings, std/std polished crank, two billet caps, 215/220 roller, roller rockers, Champion Irons, Champion intake, E85, 120's, TT chip, 72GTQ, Balanced, crack checked,reconditioned rods, Lined, etc.
Now as much as I dont want to say, but I have to becuase it plays into the fail points, Austin isnt the best tuner in the world and plays with his stereo more than paying attention to the car so it had some detonation when he was trying to get the bugs worked out. Not that he doesnt pay attention at all but he could have done a little better job at it. One of those issues was that the cam didnt have the oil groove in it and neither did the cam bearings so the drivers side wasnt getting oil to the lifters and smoked a couple pushrods and a couple cups on the roller rockers. So he took the cam in and had the machine shop cut a groove in it. Now after this, we take the car on the Long Haul, had some more knock issues on that trip but ran pretty well. He then started to have some pretty bad issues with the crankcase getting pressurized. He did a compression check and everything was good.
I know Austin well enough to know he had some fun with it after that point but supposedly it was doing well until the noght it just blew the hell out. Like I said, he says he wasnt on it.
Giving Austin the benefit of the doubt on tuning and paying some attention to knock, my theory is that there was a balancing issue with the crank and it eventually just cracked everything under the caps and then gave the crank enough room to wobble and crack. Austin thinks it's the hyper piston #5 that gave out and caused the rod to pull out of the piston and then blow everything else out. I dont think thats the case becuase I've opened up plenty of motors with broken pistons and rods through the side of the block but never seen anything take out the entire bottom end and crack the balancer and front cover, usually the rod just breaks in pieces and windows the block.
Or, I'm also thinking that Austin may be partially right. I dont know how the wrist pin gets oiled in a 4.1 but possibly the groove the machine shop cut into the cam wasnt enough and didnt supply enough oil to the wrist pin on #5. Eventually the wrist pin seizes up and breaks out of the piston??
Or was the pressurized crankcase becuase of a damaged piston skirt, or cracked piston? The piston does have a chunk taken out of the top of it but no pitting and i think the chunk is from getting the beat down once it fell out of the bore.
What the hell would case the balancer to crack in this sort of a blow out? The front caps are still intack. Or did the balancer give out and then cause this whole thing as mentioned earlier?
Now as much as I dont want to say, but I have to becuase it plays into the fail points, Austin isnt the best tuner in the world and plays with his stereo more than paying attention to the car so it had some detonation when he was trying to get the bugs worked out. Not that he doesnt pay attention at all but he could have done a little better job at it. One of those issues was that the cam didnt have the oil groove in it and neither did the cam bearings so the drivers side wasnt getting oil to the lifters and smoked a couple pushrods and a couple cups on the roller rockers. So he took the cam in and had the machine shop cut a groove in it. Now after this, we take the car on the Long Haul, had some more knock issues on that trip but ran pretty well. He then started to have some pretty bad issues with the crankcase getting pressurized. He did a compression check and everything was good.
I know Austin well enough to know he had some fun with it after that point but supposedly it was doing well until the noght it just blew the hell out. Like I said, he says he wasnt on it.
Giving Austin the benefit of the doubt on tuning and paying some attention to knock, my theory is that there was a balancing issue with the crank and it eventually just cracked everything under the caps and then gave the crank enough room to wobble and crack. Austin thinks it's the hyper piston #5 that gave out and caused the rod to pull out of the piston and then blow everything else out. I dont think thats the case becuase I've opened up plenty of motors with broken pistons and rods through the side of the block but never seen anything take out the entire bottom end and crack the balancer and front cover, usually the rod just breaks in pieces and windows the block.
Or, I'm also thinking that Austin may be partially right. I dont know how the wrist pin gets oiled in a 4.1 but possibly the groove the machine shop cut into the cam wasnt enough and didnt supply enough oil to the wrist pin on #5. Eventually the wrist pin seizes up and breaks out of the piston??
Or was the pressurized crankcase becuase of a damaged piston skirt, or cracked piston? The piston does have a chunk taken out of the top of it but no pitting and i think the chunk is from getting the beat down once it fell out of the bore.
What the hell would case the balancer to crack in this sort of a blow out? The front caps are still intack. Or did the balancer give out and then cause this whole thing as mentioned earlier?
My theory is that the Balancer tore out after the crank snapped when the front of the crank decelerated quickly (hit something or really bad vibrations) and all the mass attached (balancer, pulleys, accessories) didn't. So the balancer was essentially twisted off the front of the crank from the inertia of that mass, the balancer failed first right at the keyway then failed at the other locations due to bending.
I circled where I think I see where a crack formed and propagated in your crank. Is there anyway you can take a close-up of this area? If these are striations then they almost had to form before everything exploded and this is likely where the initial failure was.
If I remember I'll take a picture of the crank that I had that failed in the same way, the rest of the motor did not explode in my case so I know that was the only thing that was wrong.
I circled where I think I see where a crack formed and propagated in your crank. Is there anyway you can take a close-up of this area? If these are striations then they almost had to form before everything exploded and this is likely where the initial failure was.
If I remember I'll take a picture of the crank that I had that failed in the same way, the rest of the motor did not explode in my case so I know that was the only thing that was wrong.
Attachments
TR Custom Parts
Mark Hueffman - Owner
- Joined
- May 25, 2001
Beat me to it! Bet they would run that in a second.
fastblackracing
Well-Known Member
- Joined
- Apr 7, 2009
Did you pull the main caps and see signs of fretting/detonation? how did the rod bearings look, I am curious to see the caps and bearings.
- Joined
- May 26, 2001
Compared to similar damage I have seen to turbo blocks, it appears the weak link let go - the 25 year-old, well used crank let go. From the big-block Buick V-8's into the turbo V-6's, the cast cranks have shown they flex a LOT under RPM and load. 
From my point of view, the crank is the heart and soul of the engine as it takes the worst pounding of all the major components, and the cast crank was never made to support the HP and RPM levels we now call normal, even though guys say "mine has run 10's or even 9's", but for how long will it last? Never seen a forged crank do that.
A crank will flex like a snake under load, and we can see this by the main bearing wear how much more a cast crank will flex over a forged or billet crank. The extra 30#'s of a forged crank should alone illustrate that it is much stronger than a cast one.
I also think the hyper piston was a casualty of the broken crank as being brittle it just shattered as the rod was twisted, not broken like we have seen with a forged piston. Same with the cast hub, it is not a steel balancer, it broke easily as they have done before even without a broken crank.
On a positive note, no mention of the converter or trans being damaged hopefully!
From my point of view, the crank is the heart and soul of the engine as it takes the worst pounding of all the major components, and the cast crank was never made to support the HP and RPM levels we now call normal, even though guys say "mine has run 10's or even 9's", but for how long will it last? Never seen a forged crank do that.
A crank will flex like a snake under load, and we can see this by the main bearing wear how much more a cast crank will flex over a forged or billet crank. The extra 30#'s of a forged crank should alone illustrate that it is much stronger than a cast one.
I also think the hyper piston was a casualty of the broken crank as being brittle it just shattered as the rod was twisted, not broken like we have seen with a forged piston. Same with the cast hub, it is not a steel balancer, it broke easily as they have done before even without a broken crank.
On a positive note, no mention of the converter or trans being damaged hopefully!
750H.P.V6
Brutal 6 Racing
- Joined
- Sep 4, 2001
Was the crank originally from the 4.1 or was it from a turbo application? The reason I ask is that a stock crank from a 4.1 should have seen far less abuse in it's lifetime than a turbo crank that has been in service for the last 25 years or so. Based on the pics of the broken crank (which might be due to the lighting ) it looks like there might have been a crack in the rod radius which was missed when the crank was magged prior to assembly.
Neal
Neal
Pittsburghkid
Displacement Replacement.
- Joined
- Mar 22, 2009
I think the engine has already dissassembled itself. Sorry to see his misfortune. Any plans yet for its replacement?
750H.P.V6
Brutal 6 Racing
- Joined
- Sep 4, 2001
All the 4.1's I've seen had rolled fillet crankshafts not the standard N/A cranks without rolled fillets on the rod journals.
Neal
