New Project

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chief
Posts: 236
Joined: Sat Jan 04, 2003 5:51 pm

New Project

Post by chief »

Hi All,

I'm hoping to get some opinions about the feasibility of a new project.

A friend has asked me to repair a tractor part, which would require building up a worn trunnion by welding then re-machining.

The trunnion is about 2" in diameter, and attached to a lot of heat sinking metal, so I'm trying to figure out if my welding gear can do the job and get a proper attachment of the new material to the old.

My equipment is a Miller 210 mig good for about 200 amps or an OA rig. If either is adequate, I would also appreciate recommendations for a good wire or filler rod for a steel trunnion that fits into a greased bushing.
Thanks Terry
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scmods
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Re: New Project

Post by scmods »

Terry,

I'm a little confused. I can't imagine a front suspension mounted on an offset with a single trunnion. Is there another part of this assembly, like maybe another trunnion that might bolt to the other side of this part? The pictures also do not show what the back of the trunnion, inside of the forging looks like. Is it welded too? If it is, it would be a bugger to get out and would be less of a candidate for replacement. If, however, it is not welded on the inside and is a slightly smaller diameter than the trunnion, it may well be a good candidate for straight out replacement. I have had a Massey-Ferguson for many years and am well aware of their pricing, andf have had the opportunity to repair a number of worn parts over the years.

If I were repairing this, I would consider knocking the round out of the hole and turning up another piece and welding it in. Ideally the hole is smaller and allows a shoulder to be utilized for locational purposes. A chamfer at the base of the larger diameterwould allow better penetration and another chamfer would ease insertion. I am a big fan of shrink fits in these types of situations as they rely less on the weld for ultimate strength. For material, I have some Ford 9000 axles that are just about 2" diameter, but are rough forged and might not clean up to the desired diameter. The material would, however, be an excellent choice. These axles weigh 50 lbs apiece and ran $20 ea at a local scrapyard. Failing this, I would utilize a chunk of hydraulic cylinder rod, if a 2" one was available. These are case hardened, ground, and hardchromed. They require an abrasive cutoff to get through the case, but after that they saw ok. By using good carbide and coming from the face of the cut off portion, you get under the case and chrome and fracture it away. Clean out the hole good, make your part oversize and heat the forging good and red before inserting the new trunnion. Weld it in place before it cools if possible.

Given the pictures, that's how I would approach this. Once the weld is done, you're done. The material is first class in either case, way past original, and the finish is good to great.

Good Luck

Bill Walck
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Harold_V
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Re: New Project

Post by Harold_V »

I can't help but be somewhat concerned about the suggestion to weld on heat treatable materials. Some won't respond favorably, and those that will offer the risk of failure unless they are properly heat treated immediately after welding. I'd approach this with caution, especially if failure could result in injury or death.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
chief
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Re: New Project

Post by chief »

Hi Bill and Harold,

Thanks for taking the time to try to help me out.

Bill, the picture wasn't the proper angle to show the part well, I've attached three more to better illustrate. The trunnions on the yoke appear to be turned in place, I can't detect any joint on the part to show they were inserted or welded on.

Harold, your reservation is certainly valid. I am not expert by any means, but my spark tests make me think the material is iron, either cast grey iron, or malleable. And the material is definately dead soft, it files very easily. The tractor owner seems to believe the part is iron.

After the discussion I've had on the general forum, and looking at the bushings the the owner brought over this morning, I'm considering just turning down the trunnion until it's round then either machining a sleeve (shrink fit) or machining a thicker bushing. The replacement bushings are only about 1/16" thick. The only reservation I have is weakening the trunnion by reducing the diameter. Since the owner is a mechanical engineer, I will make him do the calculation :D

Terry
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warmstrong1955
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Re: New Project

Post by warmstrong1955 »

In the early 70's, we used MF30's for transportation. They had a similar set up to what you have, and they were always a problem for us, either wearing out, or breaking. (Miners are tough on things..... ) New trunnion was cheap enough back then, but we were changin' 'em faster than the dealer could supply 'em, so I did a bit of redesign.

We bored out both pins, from the large end, and welded in one custom built shaft that was machined to press into both bores. It went all the way through the center tube, much like a John Deere 4510. Looks like yours also has two different diameter trunnions as the MF30 did. If I recall, the hanger that holds both pins was malleable cast, easily weldable.

May or may not work in your case....I don't know if the long pin will interfere with anything on your tractor.

I don't have any pics of the MF30's, but they were set up like this 4510....heavy on the rear, and they did good wheelies.....
New & Shiny.JPG
Here's the 4510 front axle. It has a 2-1/8" tube that runs all the way thru, and a 3" sleeve welded on one end. This is very much like the fix I did on the MF30's.
4510 Front Axle.jpg
A more complicated way to do it, but we had a longevity problem with the existing MF design, as well as parts availability.

Bill
Today's solutions are tomorrow's problems.
chief
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Re: New Project

Post by chief »

Hi Bill,

I like your suggestion for a pin, and looking at the parts catalog for the bushing supplier, it seems they actually changed to the design you described in later versions of the tractor! I need to look at the rest of the tractor to check if there would be any interference, as you mentioned, but I think it would actually be easier to do that than to get the darn piece accurately positioned to mill the trunnion after build-up.

And yes the two trunnions are slightly different sizes, less than a 1/10" difference?? Can't imagine why the designer did that, it's practically begging to fit the wrong bushing when rebuilding.
Terry
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steamin10
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Re: New Project

Post by steamin10 »

One solution to pin failure, is to make a bigger connection to spread the load more. In simple engineering, a larger bearing surface means a lower load, and more time to suffer the wear.

Many ways to skin a cat.
Big Dave, former Millwright, Electrician, Environmental conditioning, and back yard Fixxit guy. Now retired, persuing boats, trains, and broken relics.
We have enough youth, how about a fountain of Smart. My computer beat me at chess, but not kickboxing
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scmods
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Re: New Project

Post by scmods »

Terry,

The new views explain it much better.

I like the John Deere set up much better as it eniminates the "overhung" (supported on one end only) structure and converts it to a "straddle" (supported on both ends) structure.

Harold makes a valid point in expressing concern for embrittlement in the welded pieces from applied heat. Malleable iron is produced from white iron (high carbon) and is annealed into it's current state. Obviously, it was welded to the steel tube axle, but we don't know anything about subsequent heat treating. The through shaft method would have the advantage of, should a fracture occur, the parts would be contained around the shaft and would not fail catastrophically.

Different sized parts may be to prevent improper assembly. A check of the part numbers in the parts listing would confirm some kind of difference. If the bushing in the main structure has been worn into the casting, you can probably go oversize to clean it up. As Dave said, this has the additional advantage of spreading the force out over a larger area, reducing the unit loading.

Bill Walck
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