Why do some line bore repairs not last?

Questionable wizard · Dec 22, 2019

Or even factory pin fitting.
Example: we purchased a JD 380G excavator, ran it to 5700 hours with a larger than recommended bucket on it(66" 3.3yd capacity). It does production loading of clay/loam into haul trucks. There is little rock. The operator is very careful and the machine is not abused, but he pushed it hard. All the non-greaseable pin joints are loose. If we were to keep the machine, it should had all the ears welded up and bored. Even the turntable bearing is getting loose.
Another example: JD350D excavator lower boom bushings failed(owner cut corners supplying non moly grease-machine had generous greasing, just non-moly), the non greasing ears had to be welded up for the new pin. This machine did mostly pipe work.
We've had other line boring repairs hired done. Those repairs didn't last as long as the original factory fitment. Oscillation joint on an Ingersol SD116DX roller.
I went an inspected a 637G coal scraper last week for a friend from NZ. Machine had spend all 13,000 hours at a power plant in Minneapolis. Yes coal loads like styrofoam pellets compared to clay or rock. Most of the joints were still tight. If I tried really hard, I could get the nose to rise 1/4" with the play in the cushion hitch. The machine was very straight and must of had a careful operator.
So what is the difference why some pin situations last, and others don't? Bore not perfectly round and supporting the pin adequately? Bore too large for pin from the beginning? Parent metal too soft? Ears not wide enough for the load? Surface finish too rough in the bore, so it pounds out larger in a short time?
I posted questions earlier this year about starting line boring for ourselves. Still tossing around the idea. Saw Stan's post from 2017 about a line boring setup from China.
Rolling thru the ideas of bringing bores to within 0.005" of target and finishing with a Sunnen hone(lots of those on Ebay). Getting the surface finish finer so a higher amount of metal is at target diameter. Considering finishing bores at press fit.
Flame away.

Questionable wizard · Dec 22, 2019

Thinking about the pins you buy from OEMs, they have a mirror finish. A higher amount of metal at finish diameter. I'll bet after watching several contractors complete bore jobs, their surface finish is rougher and their measuring tools may be inadaquate.

Ronsii · Dec 22, 2019

I think most bore guys like a rougher surface finish to hold more grease....

John C. · Dec 23, 2019

A lot depends on the application of the joint. A wheel loader center joint probably has less problem with metallurgy than say a bucket pin boss. I ran into the issue a bit with Komatsu WA600 bucket pin bosses. The pins has some kind of exotic case hardening and a supper smooth finish and they were matched to the bushings. If you used an aftermarket bushing the joint failed in short order. On the other hand, I've seen plenty of excavator booms redone with little to no problems. Another issue is the amount of interference fit for the bushings. One machinist that did work for me always finished the bores on the tight side of the spec. What would normally be a couple of tons of push on the bushings would for him be ten to twelve tons. They were hell to get in but I never had to go back a year or so later to redo the job. On the bores that were parent metal, I always thought that things like preheat and the metallurgy of the welding wire might make a difference. I used to stick weld the bores with 7018 going straight across the bores in stringers. There was no porosity and the welds contracted against each string which seemed to make a little easier to cut for the machinist. When the bore welders came out, I saw they all used hard wire and they ran the stringers around the bore. My thoughts on that was that they had to dump more weld in. Multiple passes to make up for the out of round meant plenty more welding on top of welding. It always seemed like the bore welders made the metal harder to cut and a few times I saw chatter in the bar and bit. Those guys kept a bench grinder close to redo the cutting edges of the bits.
Maybe others that regularly repair bores will come along with more info.

TNB · Dec 24, 2019

Questionable wizard said:
Or even factory pin fitting.
Example: we purchased a JD 380G excavator, ran it to 5700 hours with a larger than recommended bucket on it(66" 3.3yd capacity). It does production loading of clay/loam into haul trucks. There is little rock. The operator is very careful and the machine is not abused, but he pushed it hard. All the non-greaseable pin joints are loose. If we were to keep the machine, it should had all the ears welded up and bored. Even the turntable bearing is getting loose.
Another example: JD350D excavator lower boom bushings failed(owner cut corners supplying non moly grease-machine had generous greasing, just non-moly), the non greasing ears had to be welded up for the new pin. This machine did mostly pipe work.
We've had other line boring repairs hired done. Those repairs didn't last as long as the original factory fitment. Oscillation joint on an Ingersol SD116DX roller.
I went an inspected a 637G coal scraper last week for a friend from NZ. Machine had spend all 13,000 hours at a power plant in Minneapolis. Yes coal loads like styrofoam pellets compared to clay or rock. Most of the joints were still tight. If I tried really hard, I could get the nose to rise 1/4" with the play in the cushion hitch. The machine was very straight and must of had a careful operator.
So what is the difference why some pin situations last, and others don't? Bore not perfectly round and supporting the pin adequately? Bore too large for pin from the beginning? Parent metal too soft? Ears not wide enough for the load? Surface finish too rough in the bore, so it pounds out larger in a short time?
I posted questions earlier this year about starting line boring for ourselves. Still tossing around the idea. Saw Stan's post from 2017 about a line boring setup from China.
Rolling thru the ideas of bringing bores to within 0.005" of target and finishing with a Sunnen hone(lots of those on Ebay). Getting the surface finish finer so a higher amount of metal is at target diameter. Considering finishing bores at press fit.
Flame away.

Deere/ hitachi went to an oil impregnated/ bronze(?) bushing for the tool pivots on D&G series excavators that notoriously don’t last. We’ve seen failures at the bucket pivot in as low as 3000 hours with what I would describe as a better than average greasing program..we’ve been reinstalling the c series steel bushings when repairing the bores and haven’t had near as many issues. Hitachi has published a service bulletin recommending this practice.

Nige · Dec 24, 2019

Questionable wizard said:
Why do some line bore repairs not last.?

Because as RayF would say - “There are Line Borers, and there are people who call themselves line borers.”
I think there is probably a lot of truth in that.

Theweldor · Dec 25, 2019

I do quite a bit of that work in the winter. I do use solid wire with a welding system. I try to end up with the bore a '001 or '002 undersize and the buff it to size with a flap wheel. That cleans up all the imperfections and leaves a nice finish with no tool marks. It only takes a few minutes of buffing as I use 40 grit flap wheels. I also will take the last cut at no more than .010 with carbide tooling.
It does get difficult when you get one that you can throw a cat threw the bore with the pin in it. Why people run them out so far is beyond me. If they are worn excessively it is more cost effective to just replace the bosses. Air arc them off and turn out a new one. Have had pretty good luck with that approach. I am not wasting my time or their money trying to build something up more than .250.
I have had very good luck with this approach. One I did only lasted 2 yrs. and the story came out when I went back to rebore. They were digging gravel in the water and the operator told me he could not understand why it loosened up so quick. He greased it wice a week and they were running it 10 hr shifts.
"Some people"

Questionable wizard · Dec 25, 2019

I'm mainly referring to the non-greaseable ears supporting the pin. After reading through the Climax bore welder manual, setting up an tweeking the machine to get desirable filler material is a practiced art.
It would be more time consuming but may end up with a more permanent repair if the bores were oversized, and hardened bushings were shrunk and installed. Then finish honed. I believe a the bore repair tech is more of a machinist than anything else. Just happens to practice in a different setting.
Good to know about the soft bronze bushings.

TNB · Dec 25, 2019

Questionable wizard said:
I'm mainly referring to the non-greaseable ears supporting the pin. After reading through the Climax bore welder manual, setting up an tweeking the machine to get desirable filler material is a practiced art.
It would be more time consuming but may end up with a more permanent repair if the bores were oversized, and hardened bushings were shrunk and installed. Then finish honed. I believe a the bore repair tech is more of a machinist than anything else. Just happens to practice in a different setting.
Good to know about the soft bronze bushings.

Don’t take the bronze statement to heart, as I’ve never inquired about the actual type of material they are. I just know they’re magnetic, they act like galvanized when you try to torch them, they’re way lighter than their steel alternatives, the oil flies when you grind them, and you can’t weld them to shrink them...pretty much have to sawzall them out. I would be interested to know what they are if anyone can offer any insight.

Nige · Dec 25, 2019

Questionable wizard said:
I'm mainly referring to the non-greaseable ears supporting the pin. After reading through the Climax bore welder manual, setting up an tweeking the machine to get desirable filler material is a practiced art.
It would be more time consuming but may end up with a more permanent repair if the bores were oversized, and hardened bushings were shrunk and installed. Then finish honed. I believe a the bore repair tech is more of a machinist than anything else. Just happens to practice in a different setting.
Good to know about the soft bronze bushings.

I think that wear in the fixed bores is generally down to wear in the moving bores and the hammer effect it creates. Basically you have a boom, stick, bucket, whatever acting as an FBH and beating the living sh1t out of the fixed bore.

Personally I’d say that a bore repair tech is a combination of metallurgist, welder, and machinist. Because if you can’t get the first two bits right I don’t care how good a machinist you are the final product is never going to be up to snuff.

Just out of interest does the Climax Manual say anything about cutting the bore first before starting the build-up process.?

Theweldor · Dec 25, 2019

I believe all of them say it is best practice to bore them before welding. Then you have something true to set the bore welder up to.

Nige · Dec 25, 2019

Theweldor said:
I believe all of them say it is best practice to bore them before welding. Then you have something true to set the bore welder up to.

I agree with you. However "Best Practice" and what some people actually do are often very different - back to the difference between Line Borers and people who say that they can line bore.

I'd also point out that by boring oversize before welding the fusion zone is moved away from the final bore surface and makes machining an easier process as a result. This is without considering the fact that after initial machining there is a clean uncontaminated surface to enable the weld to fuse correctly to the parent metal. See the photo below. The "person who said they were a line borer" failed to cut the bore oversize before welding and couldn't understand for the life of them why this job was rejected.

Questionable wizard · Dec 25, 2019

TNB said:
Deere/ hitachi went to an oil impregnated/ bronze(?) bushing for the tool pivots on D&G series excavators that notoriously don’t last. We’ve seen failures at the bucket pivot in as low as 3000 hours with what I would describe as a better than average greasing program..we’ve been reinstalling the c series steel bushings when repairing the bores and haven’t had near as many issues. Hitachi has published a service bulletin recommending this practice.

We lost the main boom bushings on both a 350D and 380G with plenty of grease. The 350D was starting to get loose again 2500 hours after the repair when we got rid of it

ETER · Dec 26, 2019

Qw, it is interesting that you have been able to gauge the wear in the pins/bores by work type to hours in service. I don't get a lot of "data" before or after bore repairs that I do...I by no means know enough to be a SME on line boring specifically... I do enough L.B.ing to find there are nuances to every repair, like how much grease crept into the weld from in between plate surfaces (causing hardening of weld/surface), angle of grind for cutters, speeds and feed of tooling, etc. I do think Nige was spot on when he mentioned that either initial slop (clearance) or "work wear" in the pin to bush definitely accelerates (hammers) the wear in the fixed pin bore...
I would only bush fixed bores as a last resort (or unless for some reason the bushes were an OEM arrangement)...I think that a smooth pin and bore finish at a "thumb press fit" is usually the norm for static pin bores. There have been quite a few discussions here regarding the metallurgy of pins and bushings...not being a metallurgist or an engineer I try to stick as close as I can to the original design and materials unless there are tried and proven better or more modern repair methods.
Regards, Bob

Nige · Dec 26, 2019

ETER said:
There have been quite a few discussions here regarding the metallurgy of pins and bushings...not being a metallurgist or an engineer I try to stick as close as I can to the original design and materials unless there are tried and proven better or more modern repair methods.

I would also throw out there the possibility that many prople who line bore likely don't know/don't have access to the specifications & tolerances of the original design, or details of the materials involved. Therein IMHO is another difference between an LB and someone who calls himself one.

ETER said:
I would only bush fixed bores as a last resort (or unless for some reason the bushes were an OEM arrangement)...I think that a smooth pin and bore finish at a "thumb press fit" is usually the norm for static pin bores.

FWIW I agree. I'd refer to it as a "sliding (or push) fit"

Theweldor · Dec 26, 2019

ETER
You are correct in the fact that quite a few jobs have their quirks. Sometimes you have to get pretty creative to just get the equipment in there. I always try to keep the same width of the bore as the original and if one side of the bore os open and the pin is a bit longer than needed, I try to add a bit more width to that side. Even if you only gain .060 or .080 that is more support than was originally there. Quite often it is enough that you will never see it again. Works very well on the outside of the ears on a bucket. Every little bit helps.

ETER · Dec 26, 2019

I agree with you Theweldor with respect to increasing pin support surface area... Sometimes increasing pin diameter is another option.
Mass seems to be "king" generally when it comes to machinery!
Regards Bob

Why do some line bore repairs not last?

Questionable wizard

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Questionable wizard

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Ronsii

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John C.

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TNB

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Nige

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Theweldor

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Questionable wizard

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TNB

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Nige

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Theweldor

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Nige

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Questionable wizard

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ETER

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Nige

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Theweldor

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ETER

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