Making pivot pins - what kind of steel to use?

[jim_wilson]

I'd like to make some lubricatable pivot pins for the thumb on my Kubota BH77 backhoe. The factory supplied pivot pins do not have grease fittings and after the hoe sat for a number of months - I ran into a problem because one of the pins was so dry the thumb was hanging up.

I've also got an idea on how to make a "better" pin - which distributes the grease more evenly - but I'm not sure exactly what type of steel would be best suited to making a replacement pin.

Anybody have any insight into this?

Thanks!

 

[jmc]

If it were mine, I would make it out of mild steel with the idea that it is easier to replace a worn pin than worn bushings. And any steel pin would be incredibly strong in a clevis arrangement if there isn't much clearance between the two sets of "shoulders".

Another issue might be whether to have it plated or not.

 

[SPYDERLK]

I would use Gr5 if you can get it conveniently. The unthreaded shank of a big bolt is a source at Tractor Supply. Avoid drilling and grooving pins to prevent cracking. Better to grease thru the casing/bushing to spare the stress risers from modifying the pin.

 

[oldpilgrim]

Tractor supply has bins of pins.

 

[M Owens]

I would make them out of 4140 or 4340 prehard.

 

[woodchipper]

Cold roll steel should work just fine for your application. Its ease of machining, and tensile strength make this steel a good candidate for making pins. It is also easy to get,and affordable.
Bolts are cheap and a good alternative to "real" pins. Or just get ready made ones with grease nipple...

 

[Mysfyt]

I would make them out of 4140 or 4340 prehard.

These would be my first and second choice also. You can get the material from McMaster Carr. A third choice is 8620. If you have a place nearby that you could have the 4140 or 8620 heat treated, you will not be sorry.

 

[deanwerden]

just drill the pin you have for nipple?

 

[MechE1]

Agree with MOwens. 4340. Here is a sample pin we use for industrial applications. About as severe as you can get with abuse. They hold up well.

 

[Farmerford]

If the joint does not have replaceable bushings I use phosphor bronze. It is stronger than mild steel, although I think strength is not an issue because a pin sized for the bearing load is much larger than needed for the shear load.

If the joint suffers from lack of lubrication the bronze will wear before the steel. Bronze pins have been on front end loaders for over a dozen years with no problem, though I do keep them well greased.

 

[Mysfyt]

Check out McMaster Carr. They have hardened shafts that are annealed at the ends so you can machine them.
SAE 660 bronze is what you want for bushings if you go that route.

 

[jim_wilson]

Check out McMaster Carr. They have hardened shafts that are annealed at the ends so you can machine them.
SAE 660 bronze is what you want for bushings if you go that route.

Bronze? I understand that bronze is not going to rust itself into the bushings (like the lower pins in my BX23 did) - but is bronze a suitable material for pivot pins? I'm not familiar with heavier duty machinery than compact tractors - is bronze used in some applications?

 

[downsizingnow48]

I have made pins like that out of mild steel, drilled for grease.

The BH77 pin is almost totally encased in the side and center bushings, if I recall correctly, it would be difficult to break a 25mm mild steel pin.

But, for that non rotating application, I wonder if the answer might not be, a shot of some kind of high quality penetrating oil every 10 hours when you grease the tractor.

 

[downsizingnow48]

This TBN thread might have some useful information, it is on converting the BH77 to hydraulic operation. I didn't look through the whole thread but the writers must have dealt with the pin/grease question.

http://www.tractorbynet.com/forums/...20-bh77-has-anyone-considered-converting.html