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Old 01-16-2021, 10:46 PM
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Default King pins from O1 drill rod

Ive been working on the sand buggy last few weeks and I need to replace the king pins. Since the king pins were already oversized and the knuckles have wallered out, I bought some 23/32 O1 annealed drill rod from McMaster and reamed the knuckles to fit. The hardness of the drill rod is HRB 90, 50k yield. Should I try to harden and temper or run these new king pins as they are? The previous king pins came in at HRC 52, but they were "racer" king pins.
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Old 01-16-2021, 11:41 PM
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Originally Posted by arizonian View Post
Ive been working on the sand buggy last few weeks and I need to replace the king pins. Since the king pins were already oversized and the knuckles have wallered out, I bought some 23/32 O1 annealed drill rod from McMaster and reamed the knuckles to fit. The hardness of the drill rod is HRB 90, 50k yield. Should I try to harden and temper or run these new king pins as they are? The previous king pins came in at HRC 52, but they were "racer" king pins.
I see no reason to harden King pins in light use. Sand buggys are not extreme use. What does that whole rig weigh 18 to 2200 pounds maybe?? I suspect a little digging will unearth more or less consumable bushings to mate with your kingpins for cheap.
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  #3  
Old 01-16-2021, 11:59 PM
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"Sand Buggy" is kind of a misnomer. The closest sand is in Yuma, 200-250 miles away. Suffice it to say, this is a desert car and rocks are in abundance. I haven't raced this car since '84, but I still enjoy a nice romp. This car will see mostly low key use but on occasion I strap in and give it hell.

And yes, the car with me in it weighs 1850 with a full load of fuel. Could be more depending on the passenger.
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Old 01-17-2021, 08:05 AM
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Pin is easy to remove & replace.
Bushing or "wallered out hole" not so much.

Put a hardened bushing (look a drill bushing for cheap source)
in hole, use softer (but tough) pin.
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Old 01-17-2021, 10:54 AM
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Kingpin bushings are brass on big trucks.
I would try nylon bushing material for you bushings. Walking beams on cats and front end loaders work will on nylon.

Ideal for egg shaped holes as you can undersize the center hole and press it into place, then drill and ream to final ID after the install
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Old 01-17-2021, 02:23 PM
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My question is about the suitability of the annealed O1 drill rod, to harden and temper or to leave them as is.

There are brass/bronze bushings in the carrier above and below the knuckle. The knuckle wallered out because the shop that did the work honed the knuckle to the king pin diameter instead of it being a press fit into the knuckle. When you go banging thru the desert at speed, any movement will just get worse.

This is where I'm at currently. The knuckle has been reamed to 1/2 thou under the pin diameter to allow a press fit. The new pins have been machined to length, grease holes and grooves machined in each end. The bronze bushings in the carriers have been reamed to size or 1/2 thou over the pin diameter.

Today I fire up the torch and harden and temper the pins or I put it together with the pins soft.

The hardness of the new pins is 90 on the Rockwell B scale, but 50 ksi, still pretty soft

The pin that came out is 52 on the Rockwell C scale, big difference.

I haven't make up my mind yet...
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Last edited by arizonian; 01-17-2021 at 02:30 PM.
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  #7  
Old 01-17-2021, 03:43 PM
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Chances of O1 staying straight when you harden it is slim. Even when heating it in a furnace and doing everything as best as possible, it still seems to warp.


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  #8  
Old 01-17-2021, 04:44 PM
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Chances of O1 staying straight when you harden it is slim. Even when heating it in a furnace and doing everything as best as possible, it still seems to warp.


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There's my answer. Thanks, greywynd.
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  #9  
Old 01-17-2021, 11:09 PM
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Even .020-.030” of warp for what you’re doing would be a PITA. If you have extra material you could try hardening one and seeing what it does.

At the diecasting place I worked, we had vacuum heat treat furnaces, and we still had some warping and movement during heat treat of H13, A2 and M2 (our main tool steels), at least it was minimal.


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  #10  
Old 01-17-2021, 11:26 PM
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Quote:
Originally Posted by greywynd View Post
Even .020-.030” of warp for what you’re doing would be a PITA. If you have extra material you could try hardening one and seeing what it does.

At the diecasting place I worked, we had vacuum heat treat furnaces, and we still had some warping and movement during heat treat of H13, A2 and M2 (our main tool steels), at least it was minimal.


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I do have one extra, but I am going to rethink this whole rebuild. I can order 3/4" 4130 and have it here on Tuesday, machine to .005 or .010 over, heat treat and temper, then grind to size. There is no option to grind to size of the O1 as they are already to size. There is no drop dead timeline for this project so I can take my time.

Now I am in need of a toolpost grinder...

Just another project...
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