Well, I guess it's time for another post regarding the progress of the backhoe rebuild. I thought this would be simpler and maybe more straight forward than the tractor and loader. And it appears that there is more damage to all of the frame, components, pins and bushings than I reckoned. It's fortunate that I rebuilt the stabilizers and cylinders before even starting on the hoe, it's just one more thing that I don't have to do. As I disassembled all of the components, I found really extensive damage to some of the important parts that aren't readily visible until you take them apart. One of the components in particular was the lower self-centering bushing that connects the tower to the frame arm extension. It, was not only broken, but the bore boss that holds the retaining ring had been ground down to the point that half of the ring was gone. The tower had dropped down on that boss to the point that the weld fastening the ring to the frame arm extension was half gone. But again, fortunately, the bore that holds that self-centering bushing was still intact and aligned with the upper bore. I won't include it with this post but will show you in the next post how I dealt with it, but in this post I'll just show you some of the pins and bushings I machined, along with the corresponding metal grades.
This is the start of the upper pin for the backhoe tower, you can see the groove that I'm machining in that accepts the retaining snap-ring. There are grooves on each end, and when installed will have a large washer and then the snap-ring which keeps the pin in place. I chose 1045 mid carbon, 2"diameter steel to machine. It winds up being a little hard to machine, but had a correspondingly higher tensile strength and better wear characteristics than straight 1018 cold rolled steel. But keep in mind, 1045 isn't a real good choice if you have to weld it, the carbon content makes it a bad choice. A guy wants to turn it a little slower and feed it a little slower as well, with plenty of lubricant.
Here I'm boring the grease hole which will penetrate to the center of the pin, and lubricate the upper joint when installed, again remember it drills a little harder too.
Now, I'm threading with an 1/8" pipe tap and will thread in the grease zerk after inserting the pin through the yoke and bushings. It tapped just fine but with plenty of cutting oil. I think this will work fine for the upper pin.
I'm down to the last couple of thousandth's cut and really have to be careful not to take off too much metal. It's a real dance to get just the right amount of slack between bushing and pin, because if you don't have enough clearance between bushing and pin when you press the bushing into the boss, the metal compresses ever so slightly and will keep the pin from going in and conversely; if you have too much clearance s a person will have a sloppy fit and it will cause excessive ware of the pin. I used DOM for all my bushing; which is usually 1020 carbon steel. It machines well and finishes up with a smooth appearance. By the way, I learned that in most cases the bushings should be softer material than the pins and should be the wear part that is replaced for a pressed or friction fit the outside circumference of that bushing should be .001 oversized to the bore that you are going to seat it into. As a rule of thumb; if the bore is 1" then the bushing should be a thousands over, if it is 2" it should be 1 1/2-2 thousands over and so on.
Here are the two together and they fit real nice. And now I have to cut the bushing down to the right length and then press it into place. You always have to have more material than you actually need so that the lathe has something to hold onto while machining. By the way, that isn't rust on my ways, it's just the cutting fluid with some fine particles of metal mixed in.
You can see the old pin stacked on top of the new billet and that's what shape it's supposed to look like when I'm finished. I'm starting the lower threaded pin and just starting the truing cut. A guy has to prep each end so that you can get the work piece concentric with the center axis of the lathe. In this picture you can see that I've taken off a few thousand's and will turn it end for end and re-chuck it up to start the work. Now that I have a round surface for the chuck to grab it will be true to turn. Also notice how much larger the diameter of the billet is than the pattern pin, I need that extra metal to form the flange on the end of the pin. And in this case I am using 2 1/2" diameter, 8620 alloy steel for my pin stock. The tensile rating for 8620 is around 100,000 psi and the real bonus is that it is weldable and not overly expensive. At least for me, I had to really pay attention to my rpm and feed rate to machine it, it's hard.
After a lot of passes, you can see what I mean by the larger end in the chuck. The center part is the journal that bears on the self centering bushing and yoke and the end captured by the tail stock will soon become the threads of this pin.
Finally got it turned to size and polished on the main journal and ready to cut threads on the end.
Threads are cut and both reliefs grooves have been machined at each end of the center journal. I'm chamfering the end of the threads to make for an easy start of the nut that I thread on.
At this point I've cut off the excess end that was what the chuck held onto, to turn the work and I'm cutting flats on each side with the mill for my wrench to fit on. What I did was use a parting tool to get the right dimension for the thickness of the flange, while it was still chucked up in my lathe, then cut the rest of the way through with my band saw, then trued up the end on the lathe.
Here is a finished view of one half completed. I just have to un-clamp it from the vise and flip it 180 degrees and do the same to the opposite side.
Here are the finished products and you can see how they compare with the old worn out pins. Also you can see how broken the self-centering bushing housing was that I removed from the frame. The new one is to the left of it for comparison. I felt real fortunate to find a new replacement bushing, because I don't think they use that type of bushing any more in the newer hoes and that's something that I could never have manufactured!
Just a close up comparison of the old and new. I made mine a little heftier at the base flange and the upper shoulder a tad longer for better engagement of the bore of the tower.
This picture just gives a closer look of those pins. Remember, the straight one with the grooves at each end is for the upper part and the one with the threads is for the lower part.
