Welding bosses on boom at boom to stick instead of line boring?

I've got an IHI 80 mini excavator that I'm rebushing and have a lot of wear in the boom at the boom to stick area. After taking it apart the bushings in the stick were not pressed in very tight and came out pretty easy. After getting the new bushings I figured the stick needs to be line bored and have a local machine shop that will oversize the hole and install a sleeve so the oem bushings fit tight again. The other issue is the boom has a lot of slop on the ears where the stick mounts and needs to be resized also. The machine shop can't do this as they can't get the machine inside and I'd have to take the boom off to do the job, which I prefer not to do. A local line borer wants about $1300 to do this job and is pretty busy right now. My question is couldn't I just have some bosses made of some 4140 and weld them to the sides of the boom? I'd like to use a custom pin anyways as the oem retention system is really bad at that area and what caused the problem in the first place. Right now the way the boom is, the pin only contacts about an inch on each ear of the boom. I figured I could put a 3 inch boss on each side of the boom and that would be plenty strong enough. I also would have one of the bosses drilled and the pin and use that as a retainer. I think the hard part would be getting everything squared up properly so the stick is square to the boom. There's obviously a trick to do this. Any advice?

I would reccomend not cutting off the ears on the boom and not bore it to insert a sleeve to press in a busshing. Spend the $$ to get it done right the first time and get it welded up and line bored to the size needed. It`s not a question of welding them on to stay, but it would still need line bored as they will not be in alignment from welding and more than likely not the proper diameter from the heat.
Would also suggest not boring it out to sleeve it as now you have two items to wear out. The bushing bore itself and the bore for the sleeve. Spend the $$ and do it right the first time.

Just bite the bullet and line bore it. Trying to weld on bosses is not only a matter of trying to keep them straight, but also fighting any distortion in the boom/boss caused by the heat of welding. In other words, it will probably need a slight align bore anyway.

I was only going to weld the bosses on the outside of the existing ears. Would never actually consider cutting the ears off and replacing them. One hole on the boom is very close to spec and one is pretty bad. Figured I'd push the pin all the way through to hold the bosses through then tack them in place. Then when I get the stick back on I would do the final welding all around the bosses. Figured it be better than the original design and have more wear surface. The stick is what the machine shop wants to bore and sleeve. They say they do it all the time.

Do it right. Line bore to clean up, weld until it's undersize, then finally line bore to size. You can correct the "loose" fit of the bushes while you're at it.

The machine shop can say whatever they like but that still doesn't make it right ....... ask them if they have a wire feed welder that fits in their line boring rig for building up bores internally and when they answer no you'll understand why they want to bore it and sleeve it.

Yair . . . .

giannid. In remote areas and back in the days before portable line boring had been invented this style of repair was a very common fix on loader buckets and linkage, parallelogram linkage on dozer rippers and so on.

It does work and, as you say, can gain some extra wear surface . . . the down side is with the bosses welded on the outside you have some unsupported pin.

I used to build/modify machinery with larger ears counterbored to locate weld on wear bosses that could be gouged off and replaced. The boss extended back through the ear to avoid the problem of an unsupported pin. There are thousands of applications for this method I have never seen it used in a production machine

As you realise and (others have mentioned) there can be hassles setting it all up but your friends are a large square, a tape, judicious welding and a Mississippi hone.

I will be shot down in flames for encouraging such heretic but behaviour but thought I should mention that it has all been done before (successfully) and you are not alone. (big grin)

Cheers.

Seems odd to me that the holes would be hogged on this little machine unless the bushing were worn completely through. As far as your boss-welding idea, be aware that no matter what, the pin is going to be very tight without some slight alignment boring. It is impossible to keep the bosses perfectly in line while welding. However, as long as you could get the pin through it is of little concern because the pin doesn't rotate there. Scrub has a very good point, though, about the unsupported pin bit. Might not ever be an issue, but if it is, that would be kind of messy.

Have you tried the new bushings in the bores? They might be tight enough, especially if this isn't going to be your bread and butter machine. Worst case, you end up line boring it anyway and waste the time and money you put into it now.

I don't see how you gain anything from adding outside bushings to support the ends of a longer pin, it changes the force on the pin from shear to bending and causes more problems than it helps.

Well gentlemen, I'm not trying to rig anything up and just looking for some suggestions and maybe make things better than oem. The machine was used as a rental and was abused a bit. I purchased it to replace an older machine and don't mind doing some repairs as I'm handy. The factory pin retention system at the boom to stick is a very bad design. It used a square plate welded to the end of the pin and a piece of metal on the boom that would keep the square plate on the pin from rotating with a large nut on the pin to keep it tight in the boom. Obviously it failed after a while and the pin started turning where it shouldn't. I just figured the ears on the boom only contact the pin 1 1/2" on each side and if I weld on 3 inch bosses on both sides of the boom, I'd have double the surface area. I also want to use one of the bosses with a bolt through the pin to keep the pin from moving, a much better way than oem. The bushings in the stick came out pretty easy. I can push the bushings in almost halfway before they start to get tight. It's a few thousands oversized for sure but only one the ends. I obviously want it fixed right. I didn't really see a problem with oversizing the stick and pressing a sleeve in for the oem bushings to fit. I thought it was a good fix but I may be wrong. I guess you could even weld the sleeve in. Just looking for some options. Line boring isn't very cheap around here. At over 1K per hole, I'm looking for some options. I've got over 2k in pins and bushings and am not even doing all them.

I can push the bushings in almost halfway before they start to get tight

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The new bushes should not even enter the bore, it's probably egged anything up to about 5 thousandths oversize.

Line boring isn't very cheap around here

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Good line boring is never cheap, but it is good ......
Think on this, it used to cost us $35k to get all the holes in our big loader buckets plus the end of the lift arm rebored. 6 holes in total.

Don't press any bush into a bore, freeze it with either dry ice or liquid nitrogen and let it expand then it will never move.

Although I've never worked on an IHI machine the pin retention system you describe is relatively common and works perfectly adequately provided the pins are greased regularly and the bolt tightness is checked every once in a while.

giannid said:

I can push the bushings in almost halfway before they start to get tight....

I obviously want it fixed right.

I've got over 2k in pins and bushings

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Never mind my previous answer. This isn't new technology, chances are you're not going to improve on the original design.

Regardless of what I do as far as line boring, the pin is getting replaced with a longer one with a boss welded to the boom with a bolt through the boss and pin to keep it from moving. I have a friend with a smaller IHI excavator that the pin configuration at the stick to boom and it's also starting to twist. He's going to modify it to something better to keep the pin from spinning.

Has anybody any thoughts on using expander pins for a job like this . I have serious wear on the Ex 200 in the boom bosses . The stick and stick pin and bushes are very good but the bosses are brutal . Something will have to be done if I can sort the tracking .

Volvomad said:

Has anybody any thoughts on using expander pins for a job like this . I have serious wear on the Ex 200 in the boom bosses . The stick and stick pin and bushes are very good but the bosses are brutal . Something will have to be done if I can sort the tracking .

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It's been tried before and doesn't work. The expanding pins are not strong enough and fail.

I'm wondering if maybe I should build the bore up with weld in my stick and then take it to the machine shop if they can't weld there? Or does this have to be done with the boring machine? The stick really doesn't need much material added as it's only a few hundred thousands over. The ears on the boom is the bad part as one side is really sloppy .

The accepted procedure used by all good line boring outfits for recovery of a damaged/oversize bore is generally done in 3 stages: -

1. Bore the diameter about 3mm (1/8") oversize, maybe more, a lot depends on the original bore size. This gets the bore circular and also removes any heat-affected metal on the surface of the bore, and provides a good key for the welding. It's not good practice to weld direct to a surface that could be contaminated with oil, grease, etc, There is too much of a danger of having areas where the weld does not penetrate or fuse correctly to the structure
2. Build up with weld until the bore is about 2-3mm undersize. Having cleaned up the bore initially the weld will be of uniform thickness, lack of penetration/fusion will not be an issue, and the weld fusion zone will be approximately 1-1.5mm below the surface of the finished bore size so there is no chance of the machining operation touching the fusion zone because that metal has a tendency of sometimes being a tad on the hard side.
3. Machine to final size.