Threading a Grade 8 bolt?

[69427]

I need to add a few more threads to one of the sway bar link bolts to make sure I've got enough adjustability so there's no preload in the bar. The bolts are grade 8 fine thread (I'm sure grade 5 would be sufficient, but these are what I've got at the moment). Before I risk damage to my die piece (as I've never tried to thread a grade 8 bolt before) is this going to be a problem? If so I'll just get a grade 5 bolt next time I'm at a hardware store. If not then I'll save some time not looking for a new bolt and modify this one. So, any thoughts on this?

Thanks,
Mike

[Twin_Turbo]

No it will thread the pre cut threads just fine but the threads will all be cut because they are originally rolled and as such the thread profile is a little different. The problem could arise when you get to the threaded portion, depending on the OD there it may or may not be possible to thread it.

But...cant you add a little spacer bushing or whatever to solve the issue??

[turtlevette]

Originally Posted by Twin_Turbo

No it will thread the pre cut threads just fine but the threads will all be cut because they are originally rolled and as such the thread profile is a little different. The problem could arise when you get to the threaded portion, depending on the OD there it may or may not be possible to thread it.

But...cant you add a little spacer bushing or whatever to solve the issue??

I think he'd have to turn down the unthreaded portion? The thread profile on a grade 8 is different? Not different enough to prevent using a grade 5 nut with a grade 8 bolt. I don't think.

The fact that you know that though is amazing. I've never ever said that you weren't a brain.

[69427]

Well guys, I played around a bit to check out my options. I originally did shim up the link to make it work, but it was such a PITA to get all the slop out and get enough compression on the urethane pieces (bushings?) that pinch the end of the sway bar. I measured the grade 8 bolt (and a similar grade 5 piece) and all I can see is about 1-2 thousandths of an inch difference between the thread OD and the shank(?) OD of each bolt. I took the (extra long) grade 5 bolt and added about 3/4" more threads to the threaded section, and then cut the hex head off it, and then threaded the top inch of it to make it adjustable for height/length. This will give me enough threads to put a jam nut against the heim (at the LCA) to prevent the bolt/stud from backing out, and also allow a jam/adjuster nut against the tube spacer (between the heim and the bushing under the bar end) to get the slop out of the link, and then a nut at the top of the stud to compress the top bushing. I think this will work, but I have to get the tires on and the car back down to ride height. (Eventually I want to cut the ends off the sway bar and put heim compatible ends there, and get rid of the urethane bushings entirely.)
Thanks for the input guys. It's given me some things to think about during this.

[Twin_Turbo]

Originally Posted by turtlevette

I think he'd have to turn down the unthreaded portion? The thread profile on a grade 8 is different? Not different enough to prevent using a grade 5 nut with a grade 8 bolt. I don't think.

The fact that you know that though is amazing. I've never ever said that you weren't a brain.

no, rolled threads and cut threads, the cut thread has a much sharper profile, if you go over them with a die you will remove material, and not just a little either. The real problem for this particular issue is the body diameter. Cut threads have a body diameter that is the same as the thread majro diameter, rolled threads are rolled from a section that has a same diameter as the minor diameter and the threads are rolled and "squeezed" into shape. A lot of automotive fasteners have a section where they are threaded and the body diameter of the rest is actually increased so it's tight in the hole. This section can be a bitch to thread, so either you get stuck or the threads won't form properly because the body diameter is too small.

[mrvette]

Originally Posted by Twin_Turbo

no, rolled threads and cut threads, the cut thread has a much sharper profile, if you go over them with a die you will remove material, and not just a little either. The real problem for this particular issue is the body diameter. Cut threads have a body diameter that is the same as the thread majro diameter, rolled threads are rolled from a section that has a same diameter as the minor diameter and the threads are rolled and "squeezed" into shape. A lot of automotive fasteners have a section where they are threaded and the body diameter of the rest is actually increased so it's tight in the hole. This section can be a bitch to thread, so either you get stuck or the threads won't form properly because the body diameter is too small.

Edjemakating, the stuff I never knew, guess I have never rethreaded bolts, can't recall ever having done it anyway....

[Ralphy]

The thread rolling I've seen, the material is smaller in diameter before being rolled. I think it's app. the pitch diameter. Also a rolled thread is much stronger. So if you cut additional threads you will compromise the strength. My guess is grade 8 bolts are cold rolled.

I used to work in the precision screw manufacturing shop, ball screws and acme screws. The lower less accurate ball screws were hot rolled. Below is one, on the major diameter you can see a line in the middle where the metal rolled toward the middle. High dollar CNC type ball screws are precision ground.



Ralphy

[GT6Steve]

Where the cut threads stop on the shank of the bolt there is gonna be one hell of a stress riser which would lead to failure in a more stressed situation. While you'll likely be fine in this application it is generally considered to be a BAD solution.

Steve

[68/70Vette]

I wonder what the expense would be to have bolts custom made? Do you have to order 100, 1000? I'm thinking now of of the trailing arm bolts. The repro bolts are incorrect.

[GT6Steve]

ARP used to do any custom thing you wanted relatively inexpensively. The Triumph GT6/TR6 head studs in their catalog are to my spec.

Nowadays they are so much bigger I'm not confident they'd be so amenable but it's worth asking....