Kingpin to bell crank arm attachment

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thebuildist United States of America
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Kingpin to bell crank arm attachment

Post by thebuildist »

Advice question: When I built my new front axle, I located the bell cranks, (aka the steering arms) up on top of the axle, on the upper side of the kingpin.

The hydraulic steering cylinder itself is attached to a steering arm down under the axle, at the bottom of the kingpin.

So, on the right side, the hydraulic steering cylinder moves the lower steering arm, and the righthand hub/spindle assembly with it.

When the righthand hub spindle pivots, the kingpin turns the right hand upper bell crank (steering arm), and that's attached to the tie rod, and the tie rod makes the lefthand bellcrank/steering arm move, so both steering spindles pivot together.

The upper bellcrank/steering arm is attached to the kingpin with a 1/4" roll pin.
2022-11-21 17_58_32-DeltaCad - [ROLL PIN.MC _].png
Today the righthand roll pin apparently sheared off. Because the righthand spindle assembly and kingpin are moving, but the steering arm, and the whole lefthand spindle assembly are sitting still.

This makes it challenging to drive the tractor.

:violin: :violin: :violin: :geek: :geek: :geek:

My engineering reference told me that that roll pin should have 4000 lbs of shear strength, which I thought would be more than plenty.

I apparently thought wrong.

The same part on whatever farm tractor has the steering arm attached/locked in place via a spline.

I presume I'm going to have to tear it apart and cut a spline on the kingpin and the inside bore of the upper steering arm.

That's going to be a REAL pain.

Any other ideas before I do all that work?

Bob
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Spike188 Canada
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Re: Kingpin to bell crank arm attachment

Post by Spike188 »

I was thinking a 6mm taper pin https://spaenaur.com/catalog/E92/ because they are rated at 72,000 psi but calculate back to a shear strength of 3,600 psi but 18-8 dowel pins https://spaenaur.com/catalog/E82/ might do the trick. I am spoiled because this company warehouse is 20 minutes from me and delivers for $5.00. McMaster Carr may have taper pins with better specifications. https://www.mcmaster.com/taper-pins/taper-pins-5/

A .250" grade 8 bolt would probably work better.
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Re: Kingpin to bell crank arm attachment

Post by Spike188 »

There shear strength on a 1/4" grade 8 calculates out to approximatly 7,500 lbs.
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Re: Kingpin to bell crank arm attachment

Post by JSinMO »

Spike188 wrote: Mon Nov 21, 2022 7:47 pm There shear strength on a 1/4" grade 8 calculates out to approximatly 7,500 lbs.
Grade 8 bolt is what came to mind too. Be worth trying before taking it all apart. Or what about the possibility of opening the hole up and trying a grade 8 3/8-24 bolt? That would more than triple the shear strength of a 1/4 roll pin.
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Re: Kingpin to bell crank arm attachment

Post by propane1 »

Are there grade 8 bolts smaller than 1/4” ? I have a place for that if there is such a thing. 3/16” is what I need.

Noel
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Re: Kingpin to bell crank arm attachment

Post by Spike188 »

Noel, a #10 grade 8 bolt is 3/16"

#10 bolts are theoretically 0.190" and 3/16 equals 0.187"
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Re: Kingpin to bell crank arm attachment

Post by thebuildist »

It needs to have zero play, not so much as a wiggle. The roll pin, being spring loaded eliminated play. And a tapered pin would do the same.

But using a bolt is going to be tough. I could precision turn the bolt and ream the hole, but even then I think I'd need to use Loctite to eliminate play.

And that would make disassembly a nightmare.

And I'm afraid to drill it much larger than 1/4", as I'm concerned it could begin to weaken the 1" kingpin itself.

The thought occured to me to install two roll pins at right angles to each other, vertically separated by... 1/2 inch? I don't know how much separation I'd need to maintain the kingpin's strength/integrity. But I'd probalby need to pull the current kingpin and weld closed the existing hole and redrill altogether, because the current hole is right in the center of the bellcrank collar.

Bob
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Re: Kingpin to bell crank arm attachment

Post by Gordy »

How about a spirol pin? 1/4" OD and 7,800 Lbs.
image.png
https://www.zoro.com/zoro-select-spring ... TCEALw_wcB

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Re: Kingpin to bell crank arm attachment

Post by Eugen »

I have a different question for you guys: should there ever should be more than 4000 lbs force on that pin? Under normal circumstances the only force opposing the steering force is the front tires friction on the surface of the soil. I have serious doubts that opposing force is anywhere near 4000 lbs.

I'd double check the range of movement of the wheels against the full range of movement of the steering cylinder. Even a little discrepancy would cause that pin to sheer.

If that checks out my second theory is that the pin was maybe of lesser quality and nowhere near the 4000 lbs rating.
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Re: Kingpin to bell crank arm attachment

Post by propane1 »

Spike188 wrote: Mon Nov 21, 2022 8:20 pm Noel, a #10 grade 8 bolt is 3/16"

#10 bolts are theoretically 0.190" and 3/16 equals 0.187"

Thanks Spike.

Noel
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