Tecnically Acceptable Repair?
#1
Crank Pulley Problem
I had the same thing happen to mine at about 2300 miles. It is at the dealer awaiting parts. A front suspension part was the only thing that kept the bolt from coming all the way out. They say there is no risk of any internal damage. Would anyone care to comment on that? The dealership has been far better than expected, but I also hate having something like this make me wonder about the car.
#2
Burning Brakes
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Originally Posted by bangbgC6
[QUOTE=UBETRUN]Happened to mine with 120 miles on the odometer. I can't remember if I read it here or heard it somewhere else but the problem only happens when the car is shifted at full throttle. That story made sense to me, I don't believe in breaking motors in gently A couple of good heat cycles and then it's time to seat the rings...
I just got to work today and brought the Vette my drive is 100 miles of wide open desert and mountains. It seems to be doing quite well now, 1490 miles and hit 142 mph this morning, it was only getting wound up. I pulled a couple of .74 g corners and I think hit redline more than a few times and best of all it still running great.. WHAT A BLAST!!!!!!! [/QUOTE]
Where can you get up to 142 (?)...so much traffic!
#3
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Originally Posted by bangbgC6
Many forum readers suggested single or double keying the pulley to the crank as an acceptable solution to the problem. I guess this a method utilized by builders that install superchargers.
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As far as I can tell the repair is satisfactory, I was only wondering if there was any need for the additional steps of "keying" the components to secure the pulley and crank together or is what has been done to correct it "technically acceptable".
...
As far as I can tell the repair is satisfactory, I was only wondering if there was any need for the additional steps of "keying" the components to secure the pulley and crank together or is what has been done to correct it "technically acceptable".
If the end of the crankshaft is tapered, they are using the center bolt to pull the harmonic dampener up onto the taper by stretching the bore of the dampener slightly. The resulting slight interference fit would allow the dampener to transmit low torque needed to run the accessory belt without a key. If the bolt loosens even slightly, you lose the interference fit and the accesories quit running. As the bolt loosens further, the dampener/pulley goes wobbly (belt frays), and finally if the bolt comes out, things really get destroyed. The time required for the entire process would depend on the rpm when the bolt loosens.
The only function of keys is to transmit torque through shear force across the key cross-section. People using keys for superchargers are transmitting more torque than the dampener/shaft fit was designed to carry, and they are augmenting the fit with keys. A key or keys, will not help your bolt loosening problem.
Further, cutting keyways in the crankshaft snout would be no easy task. I believe the only practical way to cut keyways in the crankshaft snout would be to remove the engine from the car and remove the crankshaft from the engine. I doubt that GM would pay for this work under warranty ($$$$), so you would be on your own.
The diamond embedded washer is in fact a high-tech lock washer and should stop the bolt was loosening up. I think I would give GM and the lock washer a chance...put it out of your mind and drive the car like it was meant to be driven. Then, if fails, the fix didn't work and the expense is on GM.
#4
Originally Posted by JmpnJckFlsh
I expect the harmonic balancer or dampener already has at least one key. It would have to have a key unless, of course, the crankshaft has a tapered snout. That could explain why the center bolt torque is so high. I have not heard about the LS2 having a tapered snout without a keyed dampener, but I am not that familiar with this engine.
If the end of the crankshaft is tapered, they are using the center bolt to pull the harmonic dampener up onto the taper by stretching the bore of the dampener slightly. The resulting slight interference fit would allow the dampener to transmit low torque needed to run the accessory belt without a key. If the bolt loosens even slightly, you lose the interference fit and the accesories quit running. As the bolt loosens further, the dampener/pulley goes wobbly (belt frays), and finally if the bolt comes out, things really get destroyed. The time required for the entire process would depend on the rpm when the bolt loosens.
The only function of keys is to transmit torque through shear force across the key cross-section. People using keys for superchargers are transmitting more torque than the dampener/shaft fit was designed to carry, and they are augmenting the fit with keys. A key or keys, will not help your bolt loosening problem.
The only function of keys is to transmit torque through shear force across the key cross-section. People using keys for superchargers are transmitting more torque than the dampener/shaft fit was designed to carry, and they are augmenting the fit with keys. A key or keys, will not help your bolt loosening problem.
Further, cutting keyways in the crankshaft snout would be no easy task. I believe the only practical way to cut keyways in the crankshaft snout would be to remove the engine from the car and remove the crankshaft from the engine. I doubt that GM would pay for this work under warranty ($$$$), so you would be on your own.
The diamond embedded washer is in fact a high-tech lock washer and should stop the bolt was loosening up. I think I would give GM and the lock washer a chance...put it out of your mind and drive the car like it was meant to be driven. Then, if fails, the fix didn't work and the expense is on GM.
Even a *slight* error in either taper can cause the dampener to snug up on the taper before pressing hard enough against the washer for the washer to do any good. Cutting accurate mating tapers is one of the hardest machining tasks to get right. Three things have to be exactly right on each mating part, the starting diameter, the angle of the taper, and the finish diameter. Get even one of them off even slightly and the interference fit will occur at a depth different than intended.
In my, slightly antiquated, engineering opinion, GM screwed the pooch with this design. They should have stuck with the tried and true keyed approach used successfully on 98,000,000 small block Chevy engines since 1955. You've never heard of this sort of problem with any of them.
#6
Safety Car
Originally Posted by RX4WRK
[/FONT]
I just got to work today and brought the Vette my drive is 100 miles of wide open desert and mountains. It seems to be doing quite well now, 1490 miles and hit 142 mph this morning, it was only getting wound up. I pulled a couple of .74 g corners and I think hit redline more than a few times and best of all it still running great.. WHAT A BLAST!!!!!!!
I just got to work today and brought the Vette my drive is 100 miles of wide open desert and mountains. It seems to be doing quite well now, 1490 miles and hit 142 mph this morning, it was only getting wound up. I pulled a couple of .74 g corners and I think hit redline more than a few times and best of all it still running great.. WHAT A BLAST!!!!!!!
Ft. Tejon Road westbound towards Mt. Emma Rd south east of the Lancaster area up towards Littlerock resevoir. The road is south of the main road and is not heavily traveled.
This thread is old, I've had the Vette up to 165 since then.
#7
Making CFOT Great Again
Originally Posted by RX4WRK
Where can you get up to 142 (?)...so much traffic!
And I'm not the only one: I saw a DSOM convertible heading eastbound just before I started my little speed run. He had probably just finished his...
#8
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Originally Posted by shopdog
Unfortunately, that is the way it is built.
I disagree. It is the inertia loading of a quick RPM change that torques the dampener, the attached pulley, and ultimately the bolt head. Stopping the dampener from slipping will stop the bolt from loosening.
A "dutchman" can be installed without removing the engine from the car, or the pulley and dampener from the crank. All you need is a mag base drill to drill a hole in the joining line between the dampener and the crank snout. Then you drive in a round pin. This gives the functionality of an ordinary key without the necessity of machining square slots in the mating parts. (You get half-round slots instead.)
It *may* work. It is far from certain, however. GM wants the washer placed between the dampener and the flange of the crank snout. That's where it has to be, of course, but because the snout is tapered, as is the dampener, the dampener won't necessarily press hard enough against the washer for it to work when the bolt is torqued to specification.
Even a *slight* error in either taper can cause the dampener to snug up on the taper before pressing hard enough against the washer for the washer to do any good. Cutting accurate mating tapers is one of the hardest machining tasks to get right. Three things have to be exactly right on each mating part, the starting diameter, the angle of the taper, and the finish diameter. Get even one of them off even slightly and the interference fit will occur at a depth different than intended.
In my, slightly antiquated, engineering opinion, GM screwed the pooch with this design. They should have stuck with the tried and true keyed approach used successfully on 98,000,000 small block Chevy engines since 1955. You've never heard of this sort of problem with any of them.
I disagree. It is the inertia loading of a quick RPM change that torques the dampener, the attached pulley, and ultimately the bolt head. Stopping the dampener from slipping will stop the bolt from loosening.
A "dutchman" can be installed without removing the engine from the car, or the pulley and dampener from the crank. All you need is a mag base drill to drill a hole in the joining line between the dampener and the crank snout. Then you drive in a round pin. This gives the functionality of an ordinary key without the necessity of machining square slots in the mating parts. (You get half-round slots instead.)
It *may* work. It is far from certain, however. GM wants the washer placed between the dampener and the flange of the crank snout. That's where it has to be, of course, but because the snout is tapered, as is the dampener, the dampener won't necessarily press hard enough against the washer for it to work when the bolt is torqued to specification.
Even a *slight* error in either taper can cause the dampener to snug up on the taper before pressing hard enough against the washer for the washer to do any good. Cutting accurate mating tapers is one of the hardest machining tasks to get right. Three things have to be exactly right on each mating part, the starting diameter, the angle of the taper, and the finish diameter. Get even one of them off even slightly and the interference fit will occur at a depth different than intended.
In my, slightly antiquated, engineering opinion, GM screwed the pooch with this design. They should have stuck with the tried and true keyed approach used successfully on 98,000,000 small block Chevy engines since 1955. You've never heard of this sort of problem with any of them.
Usually, on parts where rotation will loosen the fastener, they design rotation such that inertia will tighten the fastener, or use a left hand thread that will tighten rather than loosen. Changing the small block rotation would be unthinkable at this point, and using a left hand thread would result in moron gorilla technicians finding a way to twist them off in the crankshaft.
If they had to have a tapered shaft, maybe they should have gone with a full hydraulic fit...no center bolt required except for the pulley. The dampener is bored for heavy interference fit when properly seated. O-ring grooves are machined into the dampener hub with hydraulic fluid passages to the outside. When you are ready to remove the dampener, you install fittings and use a hydraulic pump to pressurize the dampener bore to expand it...pops right off. No problem transmitting ANY torque you want through the dampener, no keys, and no bolt to loosen. Standard procedure on heavy machinery.
#9
Originally Posted by shopdog
In my, slightly antiquated, engineering opinion, GM screwed the pooch with this design. They should have stuck with the tried and true keyed approach used successfully on 98,000,000 small block Chevy engines since 1955. You've never heard of this sort of problem with any of them.
#10
Safety Car
Originally Posted by c2c4c6
Does anyone know what the fix is from GM powertrain on the newer engines that are now being delivered? Do they use the same diamond washer or do they have a different fix on those engines?
#12
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CI 1-4-5-8-9-10 Vet
St. Jude Donor '03,'04,'05,'07,08,'09,'10,’17
Originally Posted by JmpnJckFlsh
If they had to have a tapered shaft, maybe they should have gone with a full hydraulic fit...no center bolt required except for the pulley. The dampener is bored for heavy interference fit when properly seated. O-ring grooves are machined into the dampener hub with hydraulic fluid passages to the outside. When you are ready to remove the dampener, you install fittings and use a hydraulic pump to pressurize the dampener bore to expand it...pops right off. No problem transmitting ANY torque you want through the dampener, no keys, and no bolt to loosen. Standard procedure on heavy machinery.
#13
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St. Jude Contributor
Originally Posted by Speed Inc.
BTW, I was told mine was only the 3rd in the country that came in for this problem.
Tom
Tom
Like the dealer would know how many are serviced for this failure. More than three....
#14
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Originally Posted by SimpsonH
...keys should only be used for alignment. Keys should not carry load.
I worked on a 3500 hp centrifugal compressor once with a straight shaft end and keyed coupling hubs. I believe it had two 1/2" square keys 180 deg apart. Regardless of how tight the "slip" fit was, the shaft was subject to fretting in the hub fit area and eventually shaft failure through cracking in the keyway...that illustrates why keys typically should not be loaded.
#15
Safety Car
Originally Posted by WhiteC5Vette
Like the dealer would know how many are serviced for this failure. More than three....
My crank pulley failure was on October 15, 2004 and I was told by GM during the case investigation that it was the third failure of a production vehicle, so FYI it wasn't the dealer that told me it was GM.
My car now has 7,900 miles and runs like a Bat out of Hell.
BTW, MY dealer was great during the whole thing, unlike many of the horror stories I hear on this forum from other Vette owners. I got treated like a King and would do it all over again if given the opportunity.
Last edited by bangbgC6; 03-08-2005 at 10:33 AM.