Crank bolt issue - WHAT is the cause? WHY does the bolt loosen?
03-19-2005, 09:37 PM
#1
Melting Slicks
Thread Starter
Crank bolt issue - WHAT is the cause? WHY does the bolt loosen?
WHY does the crank bolt come loose? Is it an issue with the bolt, or washer, or crank...? Is the bolt simply not torqued correctly at the factory? Is it an issue where the bolt is not sized correctly? There must be a REASON for this.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
03-20-2005, 02:02 AM
#2
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Originally Posted by Vet
WHY does the crank bolt come loose? Is it an issue with the bolt, or washer, or crank...? Is the bolt simply not torqued correctly at the factory? Is it an issue where the bolt is not sized correctly? There must be a REASON for this.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
Washer that isn't up to the task - new washer solves the problem.
03-20-2005, 10:59 AM
#4
Drifting
Originally Posted by DryHeat
Did GM eventually address the problem in later runs? My VIN is 08194- do I need to even worry about this problem? 
I believe the breakpoint where the problem was addressed is VIN 11039. All VIN's under this need to be checked IMHO, even though the percentage of cars with this problem seem to be low.
03-20-2005, 11:04 AM
#5
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Originally Posted by Brett Hunter
I believe the breakpoint where the problem was addressed is VIN 11039. All VIN's under this need to be checked IMHO, even though the percentage of cars with this problem seem to be low.
While I was in BG picking up my vert, during the plant tour this came up, and as stated above...even though the number of cars with the problem was low, they identified the fix and hopefully this has eliminated the problem from VIN 11039 forward. 
03-20-2005, 02:47 PM
#7
Originally Posted by Vet
WHY does the crank bolt come loose? Is it an issue with the bolt, or washer, or crank...? Is the bolt simply not torqued correctly at the factory? Is it an issue where the bolt is not sized correctly? There must be a REASON for this.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
Gee, what about just drenching the bolt in thread-locker and putting a heavy duty lock washer under it...?
What about just re-torquing the bolt only? If it's loose and you re-torque, will it become loose again on it's own?
I'd love to the know CAUSE of this wacky problem.
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
03-20-2005, 03:53 PM
#8
Originally Posted by shopdog
The harmonic dampener isn't keyed to the crank. It was in 98,000,000 previous generation small blocks. This heavy weight is only held to the crank by friction. Under high inertia loads (rapid change in engine RPM), the dampener can slip on the crank snout. This is a problem because the crank pulley is attached to the dampener, and the head of the crank bolt is pressed hard against it. So the bolt is unscrewed by the slipping dampener.
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
03-20-2005, 04:28 PM
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Originally Posted by shopdog
The harmonic dampener isn't keyed to the crank. It was in 98,000,000 previous generation small blocks. This heavy weight is only held to the crank by friction. Under high inertia loads (rapid change in engine RPM), the dampener can slip on the crank snout. This is a problem because the crank pulley is attached to the dampener, and the head of the crank bolt is pressed hard against it. So the bolt is unscrewed by the slipping dampener.
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
03-20-2005, 06:45 PM
#10
Safety Car
Originally Posted by shopdog
The harmonic dampener isn't keyed to the crank. It was in 98,000,000 previous generation small blocks. This heavy weight is only held to the crank by friction. Under high inertia loads (rapid change in engine RPM), the dampener can slip on the crank snout. This is a problem because the crank pulley is attached to the dampener, and the head of the crank bolt is pressed hard against it. So the bolt is unscrewed by the slipping dampener.
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
(Note that you don't have to be razzing the engine when it ultimately fails. Once the bolt starts to loosen, it doesn't take much to make it loosen further, and cause the belt shredding which is the ultimate failure.)
GM's "fix" is to add an abrasive washer between the dampener and the shoulder of the crank. The idea is to increase friction so the dampener won't slip on the crank snout. It is at best a marginal improvement. The correct fix would be to key the dampener to the crank as all small blocks did from 1955 until recently. GM doesn't want to do that because it would cost more. (Not much more, but pennies add up over a large production run.)
Now all of that would be incorrect if the timing marks were not on the pulley. But that would be silly.
03-20-2005, 07:10 PM
#11
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Originally Posted by TedG
You have me confused. IMHO The balancer must be KEYED to the crank. It would be virtually impossible to line it up correctly to align the timing marks. That being said, reading the replacement instructions, there is nothing about lining up anything. So that leads to the problem. It sounds like the pulley is not seated properly and is finally seating and leaving the bolt loose. Poor machining match? Anyway the abrasive washer would help when the pulley seats, but wouldn't give me a warm fuzzy.
Now all of that would be incorrect if the timing marks were not on the pulley. But that would be silly.
Now all of that would be incorrect if the timing marks were not on the pulley. But that would be silly.
03-20-2005, 07:16 PM
#12
Safety Car
Originally Posted by Av8ter
The balancer is pressed onto the crankshaft. There is no "keyed" slot as in the chevy motors of the past. The timing is maintained by 2 reluctor wheels, one on the cam and one on the crank. There are magnetic pickup sensors that read the reluctor wheels and transmit that information to the computer. The reluctor wheel on the cam is used for starting purposes only, then the reluctor wheel on the crank takes over.
03-20-2005, 07:34 PM
#13
Melting Slicks
Thread Starter
Ok, so if this indeed the problem (a balancer that shifts on the snout causing the bolt to loosen), AND if the "fix" is merely to add a special abrasive washer, then this whole issue is not really a big deal. Anyone who fears loosing the balancer can simply pull the bolt and check to see which washer they have... and if they do not have the correct washer, simply add it.
I'd probably make it routine to check the torque on that bolt with each oil change or whatever. I understand that the bolt can back out suddenly and very quickly leading to a sudden unexpected failure. But if that bolt, WITH abrasive washer, is torqued every now and then, nice and tight per the specs, the chances of the balancer slipping on the snout would be less, etc... I'd think it's better than not doing it.
I still cannot understand why they did away with the key. Is it REALLY so much more expensive to key the thing? Didn't they realize that this problem would exist, especially with this type of car/engine?
I wonder if there is any way to somehow key the balancer or add some type of locking bolt, or....??? Any ideas? The balancer could be slotted for a key, but the crank would be a problem.. not about to pull the crank.
I'd probably make it routine to check the torque on that bolt with each oil change or whatever. I understand that the bolt can back out suddenly and very quickly leading to a sudden unexpected failure. But if that bolt, WITH abrasive washer, is torqued every now and then, nice and tight per the specs, the chances of the balancer slipping on the snout would be less, etc... I'd think it's better than not doing it.
I still cannot understand why they did away with the key. Is it REALLY so much more expensive to key the thing? Didn't they realize that this problem would exist, especially with this type of car/engine?
I wonder if there is any way to somehow key the balancer or add some type of locking bolt, or....??? Any ideas? The balancer could be slotted for a key, but the crank would be a problem.. not about to pull the crank.
03-20-2005, 07:37 PM
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Originally Posted by Vet
Ok, so if this indeed the problem (a balancer that shifts on the snout causing the bolt to loosen), AND if the "fix" is merely to add a special abrasive washer, then this whole issue is not really a big deal. Anyone who fears loosing the balancer can simply pull the bolt and check to see which washer they have... and if they do not have the correct washer, simply add it.
I'd probably make it routine to check the torque on that bolt with each oil change or whatever. I understand that the bolt can back out suddenly and very quickly leading to a sudden unexpected failure. But if that bolt, WITH abrasive washer, is torqued every now and then, nice and tight per the specs, the chances of the balancer slipping on the snout would be less, etc... I'd think it's better than not doing it.
I still cannot understand why they did away with the key. Is it REALLY so much more expensive to key the thing? Didn't they realize that this problem would exist, especially with this type of car/engine?
I wonder if there is any way to somehow key the balancer or add some type of locking bolt, or....??? Any ideas? The balancer could be slotted for a key, but the crank would be a problem.. not about to pull the crank.
I'd probably make it routine to check the torque on that bolt with each oil change or whatever. I understand that the bolt can back out suddenly and very quickly leading to a sudden unexpected failure. But if that bolt, WITH abrasive washer, is torqued every now and then, nice and tight per the specs, the chances of the balancer slipping on the snout would be less, etc... I'd think it's better than not doing it.
I still cannot understand why they did away with the key. Is it REALLY so much more expensive to key the thing? Didn't they realize that this problem would exist, especially with this type of car/engine?
I wonder if there is any way to somehow key the balancer or add some type of locking bolt, or....??? Any ideas? The balancer could be slotted for a key, but the crank would be a problem.. not about to pull the crank.
03-20-2005, 07:38 PM
#15
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Originally Posted by TedG
Okey dokey. I was being silly thinking they would not key the balancer.
On the C5, you install the old crankbolt and torque to 240 ft pounds, remove that bolt, install a new bolt and tighten to 50 ft pounds and then turn it an additional 140 degrees. And believe me, its tight as hell and is not coming off.
03-20-2005, 07:43 PM
#16
Melting Slicks
Thread Starter
Originally Posted by Datawiz
Not a big deal???? Several members have lost their belts while driving which tore up the inside of their engine bay. How is that no big deal? I was lucky to catch mine before it caused any damage.
"Not a big deal" meaning that it appears to be a quick and easy fix. If one can simply pull the bolt and add a new washer, that is not a big deal.
HOWEVER, if one is not aware of this and the balancer and belt flies off and wrecks the car, that IS a big deal for sure!
Point is, it seems to be easy to PREVENT the problem, IF indeed this special washer is the magic cure. I think when I get my C6, I will probably replace the washer and retorque the bolt just for peace of mind, whether Chevy has supposedly taken care of this issue or not.
03-20-2005, 07:59 PM
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Just missed 11008 is my vin and it was built 12/4 so that must be the break build date for the fix. If mine had only been a little further down the line that day. No problems so far.
03-20-2005, 08:12 PM
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Originally Posted by shopdog
The harmonic dampener isn't keyed to the crank.
Did this start with the LS1/LS6 or the LS2?
03-20-2005, 08:12 PM
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Originally Posted by Vet
--------------------
"Not a big deal" meaning that it appears to be a quick and easy fix. If one can simply pull the bolt and add a new washer, that is not a big deal.
HOWEVER, if one is not aware of this and the balancer and belt flies off and wrecks the car, that IS a big deal for sure!
Point is, it seems to be easy to PREVENT the problem, IF indeed this special washer is the magic cure. I think when I get my C6, I will probably replace the washer and retorque the bolt just for peace of mind, whether Chevy has supposedly taken care of this issue or not.
"Not a big deal" meaning that it appears to be a quick and easy fix. If one can simply pull the bolt and add a new washer, that is not a big deal.
HOWEVER, if one is not aware of this and the balancer and belt flies off and wrecks the car, that IS a big deal for sure!
Point is, it seems to be easy to PREVENT the problem, IF indeed this special washer is the magic cure. I think when I get my C6, I will probably replace the washer and retorque the bolt just for peace of mind, whether Chevy has supposedly taken care of this issue or not.
03-20-2005, 08:30 PM
#20
Le Mans Master
Originally Posted by Av8ter
I keyed mine, 02 Z06, when I installed the supercharger. I dont exactly know why the bolt is coming loose on many of these C6's. There are 1000's of C5 running around with 1000's of miles and this has never been an issue. They must have changed hardware or the amount of torque on the crank bolt or something.
On the C5, you install the old crankbolt and torque to 240 ft pounds, remove that bolt, install a new bolt and tighten to 50 ft pounds and then turn it an additional 140 degrees. And believe me, its tight as hell and is not coming off.
On the C5, you install the old crankbolt and torque to 240 ft pounds, remove that bolt, install a new bolt and tighten to 50 ft pounds and then turn it an additional 140 degrees. And believe me, its tight as hell and is not coming off.
Most of us have not, fortunately, suffered this catastrophic failure. Hopefully, we never will. My guess (and hope) is that a properly assembled engine will not have a crank pulley issue. GM still feels this failure is not widespread enough to issue a recall for a retrofit of the new washer. At this point all I can do is monitor my belt and pulley bolt, and hope GM knows what they're doing.
