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.

 

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!

 

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.

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.

 

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.

 

You know: If it Ain't Broke...

 

Where can you get up to 142 (?)...so much traffic! [/QUOTE]

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.

 

I hit 160 yesterday on I-8 near Stanfield, AZ. The road is arrow-straight, and there's very little traffic; most of the time you're the only vehicle in sight from horizon to horizon. Which is precisely why I take I-8.

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...

 

I agree; they should have left it alone. Not sure what the motivation was...maybe saving a few bucks on machining keyways? That would be offset by the tapered snout and bore seems to me.

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.

 

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?

 

Yes, the engines utilize the DEW friction washer during assembly. There is a TSB thread floating around the forum somewhere that gives VIN ranges.

 

Not sure if the pulley-shaft have a proper taper fit, but keys should only be used for alignment. Keys should not carry load.

 

We use these on our electric driven natural gas compressors. And it is a major pain in the *** if one company makes the coupling (in this case damper) and another machines the shaft and FUBARs the machine work. Ask me how I know But those applications are for transmitting up to 15,000 HP (in our case). It would be overkill for driving accessories. In addition, the hydraulic pumps and fittings would make this task a bit more specialized than I would like to see. They should have just stuck with the old keyed shaft a la SBC . what WERE they thinking?

 

Like the dealer would know how many are serviced for this failure. More than three....

 

Technically speaking, that is correct. However, when you have a straight shaft with a slip fit on the dampener like the old small blocks, there is no alternative...the key has to take the torque load. At the low torque levels needed to drive the accessory belts (or inertia loading from high rpm shifts), key loading seems to have never been a problem.

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.

 

In case you didn't notice this thread is from November 3, 2004.

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.