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alsinaj
08-28-2006, 04:22 PM
I am writing for a friend who needs to repair a worn joint in the boom of a small excavator. The pin is about 1.25" D x 6" L. The ends of the pin are supported in two "ears" made of 1" steel plate. The pin is shot and the holes in the ears are worn oblong. There is no way to get the "ears" mounted on a machine tool, so they have to be repaired in place. Questions: 1) how to re-bore the holes in the ears so they are round and in line with each other, 2) what materials to use for the replacement pin and bushings? Equipment available: 16" lathe, vertical mill, drill press, assorted welders and hand-held power tools. Suggestions?

jmm360
08-28-2006, 04:43 PM
I'm sure the right way is to weld & line bore the bosses but without that equipment another way is to use a mag drill on the boom and make some bushings to fit, I did this for a similar sized spindle pin a couple months ago and it worked fine.

Rustybolt
08-28-2006, 06:08 PM
A cole drill and drill em out oversize and rebush.Put grease fitting in the bushings.

greywynd
08-29-2006, 12:41 AM
Not many machines are built without either bushings, or sometimes they are welded bushings that can have the weld ground off, then removed/replaced. When you say 'small excavator' I'm guessing that you are talking 5 tonnes and under.....with some ingenuity most of these machine parts can be dismantled/setup on standard mills/lathes....of course it depends on the shop and access. Somewhere on here there was a thread about line boring using a mag drill....was for a larger excavator bucket if I recall. It may have been over on the hobart welding forum too, I'll see if I can get teh cobwebs out of my memory and find it.

Almost forgot......be careful when measuring sizes on these machines, a lot of stuff is metric. I know the pins for the bucket linkage on my machine are 30mm in diameter.

Mark

Mark Hockett
08-29-2006, 01:12 AM
I've been making replacement pins for one of the local rental yards backhoes and excavators. I use 4140 HT for the pins. The rental yard has been very happy with them and says they are holding up well. On my Case backhoe I had one of the pin bores get damaged. I repaired it like greywynd described by cutting out the old bushing and welding in a new sleeve.

menace
08-29-2006, 01:29 AM
It sounds to me that the "ears" don't have any bushings in them, right? If so, I would leave the old plate where it is, make a new pin 2" longer than the old one , cut 2 peices of 1" plate to match the ears, overlay the ears and pin with new plate and end weld and plug weld the "new" ears to the boom. After that I would install a new bushing and shims in the stick along with new "grease fittings" This should work with the tools you listed as having! Good luck!

Steve

Ian B
08-29-2006, 05:40 AM
Mark,

Do you harden & temper the 4140?

(or is that what the HT stands for - excuse my ignorance)

Thanks,

Ian

deltap
08-29-2006, 07:15 PM
If the ears are large enough, torch out the worn holes to accept a piece of bushing stock long enough to go from side to side. Finish welding bushing stock on both sides. This makes alignment of the bushings easy as it is one piece. Now saw out the center portion to fit the boom. Insert grease fittings in predrilled holes. Drive pin. Done. You have a piece of bushing stock to play with on the lathe.

tattoomike68
08-29-2006, 07:24 PM
If the ears are large enough, torch out the worn holes to accept a piece of bushing stock long enough to go from side to side. Finish welding bushing stock on both sides. This makes alignment of the bushings easy as it is one piece. Now saw out the center portion to fit the boom. Insert grease fittings in predrilled holes. Drive pin. Done. You have a piece of bushing stock to play with on the lathe.

Exactly! thats the way to get it done fast and good as new. I have done it just like that. A torch will bore a hole good enough for a weld in shoulder bushing. Machining the hole is a waste of time.

Use 1018 for the bushing/pin boss and 4140 for the pin. no need to harden the pin.

greywynd
08-30-2006, 12:49 AM
I've also used hardened H13 for pins and they seem to stand up well. (Helps that I can get it heat treated where I work). I've also seen guys use cold rolled steel for pins, and then just replace them every couple years or so, no wear to the hardened bushings. Not sure if I'd do that one, but I guess whatever works for you.

Mark