davidfarmer

Just completely my Torque sheet for the Z06 C6, and noticed that the Z06 ONLY requires you to replace the front Cam concentric bolts anytime you take them loose. I don't know if they used aluminum/titanium bolts, and they are torque-to-yield, OR if there is a problem with gauling between the bolt and the C6 Z06 subframe.

Anyway, just wanted to point it out as a warning to you z06 owners.

outnumbered

Thanks for the heads up Dave.

Dan

ghoffman

That is because of the "smashed" so called lock nuts. If they did the calcs correctly, the total torque of the fastener must consider the running torque of the nut even before it engages the part. Since the nut has different values before and after installation, that is probably what they are doing. Our camber kit is available for the C6Z (and all C5's and C6's) and unlike the stock and other setups, the clamping force of the bolt and nut to generate friction to prevent movement is not part of the equation. Our system has been proven in World Challenge, National class SCCA and Solo competition. One competitor was hit so hard that the wheel was toast, but the suspension stayed put. We recently revised the camber plates so that they are all rectangular, black anodized, and laser etched for the offset in mm. We offer a specific C6Z kit. The complete kit is still only $200 and the custom 17-4PH stud kit for the upper arms that allows rapid camber and caster changes is only $80 for the C5 and C6 and $150 for the C6Z (because of the rears so that there are 2x more of them).
Old style on far left, new C5/C6 in the center, and C6ZO6 on right.


http://hardbarusa.com/hardbar/produc...products_id=41

davidfarmer

Good info Gary. I'll have to crawl under a C6Z06 and take a look. Funny that they changed only the Z06 to this style nut.....

ghoffman

They didn't, I had them all over my C5, and I use a tap on them to clear out the smashed portion. BTW, here is a free download of ISO (metric) fastener grades versus SAE.
http://hardbarusa.com/Fastener%20Grades.xls

davidfarmer

I thought they looked familiar. I wonder why they don't require the nut replacement in the other cars. The C6 manual (online) clearly requires new nuts on the Z06's, but not on the others.

btw, I agree about the (lack of) friction causing the concentrics to rotate. However, in my experience, the only time I actually had it happen, the nut had come loose (due to a blown shock). I think it depends a lot on what part of the curve the concentric is on.

Thanks for the info.

davidfarmer

Gary, I wonder if the "squashed" nuts in combination with the Magnesium cradle has some influence in this? I don't know why it would matter, but maybe the interaction of the two together changes the torque/strain capabilities??!!

Just thinking out loud!

ghoffman

I doubt it, but who knows? The friction under the head of the fastener is such a huge component of the torque, so with a new fastener at least you are consistant. These are huge M14's so the shear area has a high margin so it must be a concern about generating enough clamping force. Check out this discussion and note how much the initial lubrication varies the torque. The only real way to do this is to directly measure strain, like you do on a rod bolt strech guage. At TRW, we used bolts with a strain guage imbedded in them for the large booster vehicle (like a Titan 4) adapter bolts. This was only used in critical situations.

What is the Proper Torque to Use on a Given Bolt
by Joe Greenslade:
http://www.zerofast.com/torque.htm

95jersey

Great, just another issue with this damn C6Z06...anyone want to buy a 4500k mile pristine yellow Z? driven once on the street because I can't get the DAMN thing to the track.

ghoffman

Calm down, there is no issue here that is not common the the C5. If anything, since the cams are bigger on the C6Z, it is less of an issue.

davidfarmer

didn't mean to stir anything up. The nut replacement was news to me, so just wanted to share the info. At this point, I'm just interested for the sake of knowledge. That's why I studied engineering, and I get very curious as to how other engineers come up with come of the things they do.

As a builder/mechanic, I also get extremely curious when servicability comes in to play. Replacing nuts/bolts on comonly swapped parts really bugs me. I'll likely just go with blue loctite in the future!