ARPS swing chain repair

[bradblazer]

I was digging out a little tree and managed to break the swing chain on my backhoe. Where the chain pins to the boom, the 9/16 link pin had a bushing on it to fit the hole in the boom which was about 0.82". The pin and bushing were hard but the hole in the boom is not. The bushed diameter should be enough to spread the load. The problem is that the bushing is not very thick and the pin was able to flex enough to crack the bushing. The hole then deformed and the pin cracked in two. I ordered a heavy duty repair link from McMaster along with some 9/16 and 7/8" W1 drill rod material. My first thought was to bore the hole out to 7/8" and make a bushing out of the larger drill rod. I was still worried about how the original bushing cracked so I decided instead to make a 1-piece fat pin by just turning down the ends of the 7/8" material. I left a radius at the base of the neck to hopefully prevent cracking. I made the new pins and then hardened them by heating to orange with the weed burner torch and quenching in water. Then I tempered them by re-heating to about 500F measured by my IR thermometer and let them slowly cool in air. I did the file test and they seemed to get nice and hard.



In these 3 pics you can see how the pins fit and how the chain attaches. This was actually earlier this summer. This past weekend I put the backhoe on for a small job and of course the other side broke so I got to repeat the repair. So far so good. The 1-piece fat pins should be much more rigid than the standard bushed pins and I'm hoping for no more problems. I never did use the new link I ordered. The 12" piece of 7/8" drill rod and the 36" piece of 9/16" drill rod were about $10/each.

[roy697]

Nice job & thanks for sharing.

[red]

Brad, great Idea!

Wasn't sure initially of your solution but the pictures made it clear. Clever machining! What about lub to reduce the wear? May not be necessary since the original set-up lasted as long as it did.

[bradblazer]

Thanks guys,
I did squirt/smear some grease over the whole thing before I finished and worked some into the joints. Those chains are one of those places I like to smear the extra gobs of grease I generate when greasing all of the backhoe pivots.

Here is a blurry pic of the rig I used to bore out that hole on the backhoe. I made an aluminum guide plug for the far end and used an annular cutter with a spring-loaded guide pin that engaged the guide plug to keep the bit straight. I clamped the whole thing to the backhoe and turned the cutter with a wrench, tightening the clamp as the cut progressed.