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The AikiHomestead

Our Lifestyle Blog as We Create a Homestead in Northern Ontario


Repairing The King Pin On My Yanmar 155D Tractor

Man adjusting a tractor tire.Tractor propped up on a log while missing a tire.Small hydraulic jack on a cinder block.Back of Yanmar tractor.Front end closeup of Yanmar tractor in the snow.Steering linkages on Yanmar tractor.Another close up view of the steering linkages on a Yanmar Tractor.Control box of Yanmar front end loader.Close up of seat belt portion of ROPS on Yanmar tractor.Man and boy posed with Yanmar tractor in winter.First off, I will apologise that there are no really good pictures of this repair “in progress”. Many key portions took place while our official blog/homestead photographer was doing other chores. In future, I’ll try to remember to snap some pictures myself, even if it means interrupting my “flow”.

As you will recall, the
Yanmar fell out of commission a few weeks ago when the king pin on the front left of the vehicle sheared completely off. Further investigation really pointed to this being a weakness in design. The “transmission” for the front wheels appears to be located directly at the wheel, beyond the axle and steering linkages. This seems to me to put some heavy torque and weight outside of the single bolt (actually the king pin) that holds the entire thing together. Not only does this pin hold the wheel and transmission to the axle, it also transfers the force of the steering wheel to both wheels via a linkage running under the tractor.

Asking Google reveals that I’m not the only Yanmar owner who has suffered this sort of fate.

Calling around, I was able to source a used king pin from Hoyes Tractors in the U. S., for US $400.00! This was not really a thought that I relished.

Instead, I called the fellow who had initially put in our driveway entrance. F! was one of those fellows that I am often in awe of – he talks casually about moving engines between dissimilar vehicles, and can throw out phrases like “I changed out the 375 for a 444 last year” (paraphrased) – things I have little to no idea of their meaning, but they sure sound impressive!

He looked over the Yanmar appraisingly last year, and even then I asked him if he would have a problem looking it over if I ever ran into trouble. At the time, it was a mystery box to me – I would sit on the seat, pull levers, and try to see what they did. Hopefully now I’m a bit more versed in its workings.

He came by to take a look at the situation, and offered some great advice about how to dismantle the last few components that were giving me a hassle. Namely the tie rods for the steering mechanism. They run from the steering wheel to a bracket above the left wheel, which, via a 90 degree linkage, travels to the right wheel. I had been unable to free the linkage from these tie rods, and with the top of the king pin still firmly wedged into it, that was a key step in getting things dealt with.

Applying a little pressure to the linkages in the direction I wanted them to go, F! suggested hammering on the outside of the coupling. It wasn’t exactly intuitive to hammer at a right angle to where you want something to move, but apparently these couplings are tapered, a bit like a cone. He predicted a dozen hammer whacks, and so it was with great admiration, they popped apart on the tenth and eleventh whack, respectively. (I’m not certain if a “whack” is an actual unit of force, but it seems close – I know a whack when I administer one – or when I have felt one…)

With the broken bits in hand, I headed over to F!’s shop, where it seems he could fix anything you care to bring him. He used a press to push the remainder of the king pin from out of the linkage (I believe he said it took about 15 tonnes of force), and we looked over the damage.

Cleaning things up, he pointed knowingly to the surface, showing where it had cracked partially in the distant past, and then fully in the more recent past. He suggested that if we couldn’t find another solution, he could possibly just weld it back together, but he didn’t seem entirely keen on that being a good or lasting fix.

Instead, he called up R! – a local fellow that seemed to be a machinist by trade, and had a small shop nearby. R! said he didn’t have time to fix it right away, but was willing to look at it if we wanted to bring it by. I loaded F! into the truck (he was nursing a broken ankle all this time), and we headed off to meet another new neighbour!

R! turned out to be another really awesome fellow. He is a pilot, having built his own aeroplane! He also was able to take in the situation with the king pin very quickly, and had a solution – boring out king pin, inserting a smaller pin inside, then welding it all together and machining it back to its original condition.

While I didn’t need the part for a week or so, as I was going to be visiting my parents with Kenny, he called within a day or two to report he was finished and I could pick it up!

After another very enjoyable visit with him, I brought the pin home, and headed off on vacation.

Back from vacation, I returned to F!’s shop to pick up the parts that I had left there. We talked at great length about many subjects (F! has knowledge and advice on just about any topic you could name. He’s a super resource for second opinions and suggestions.)

Finally, on F!’s advice, I purchased a small tube of “blue – sensor-safe gasket maker”.

Grandpa dropped by the next morning to light a fire under me on this repair, but in my defense, I was already heading out the door. I welcomed his company to help out with this, and on his suggestion, we went to his workshop to take advantage of his selection of tools, and especially a bench vice.

It was with not a little head scratching that I tried to puzzle out how to re-assemble the various bearings that were involved with this thing. It was helpful to look at the king pin itself and see the wear marks at different levels.

One difficulty right away was that nothing would fit over the key in the shaft. Grandpa pulled it out with a pair of vice grips and then things moved much more quickly. First I cleaned off the base of the king pin, and then applied a thin bead of gasket around the bolt holes, and around the perimeter of the base. I slid the casing for the transmission over the king pin, and let it come down onto the base. Finger tightening the bolts on the base of the king pin locked it nicely to the casing, and then I slid on first a small ball bearing, then the main gear. Inside this gear goes two “roller” bearings that fit nowhere else. Then another small ball bearing, then a large ball bearing, and finally, a “sleeve”.

I carefully carried this contraption back to the tractor, where I wiped off the gasket of the casing cover (which was still attached to the axle), and then slid the king pin up through another large ball bearing (which I hadn’t noticed earlier, but was still wedged up inside the casing cover), and finally up through the casing cover.

I inserted the key in the side of the top of the king pin, and then tapped on the steering linkage. Next came a stack of thin washers, followed by a larger washer and then the nut. I tightened the nut down with the largest wrench Grandpa had, and we seemed to be in business. Grandpa was a bit concerned that turning one wheel caused the opposite one to turn in the opposite direction. While I thought this was a normal outcome of a differential gear, I also wasn’t well versed enough in mechanics to outright discount his doubts. Of course, I also had to point out that we couldn’t possibly have screwed up the re-assembly of things so much as to cause this effect.

With huge amounts of WD-40 and screwing the nuts up and down the linkage shafts, we were able to free them up enough to allow us to assemble them and tighten the nuts in the proper position. These linkages don’t seem to have a means to hold the “bolt” in place as the nut gets tightened, so as soon as things begin to get tight, the nut starts to spin the bolt, and you don’t make any progress on tightening things. We needed to disassemble the linkages, hold them down lower with vice grips, and then spin the bolts up and down the shafts about three or four times before we were confident enough that they would go on without the vice grip. This did work for us.

Oh no! We had made an incorrect assumption much earlier in the process! With the keyed portion of the king pin broken off from the base, we simply eyeballed the key and judged that it was directly opposite the wheel. This was obviously not quite true upon re-assembly, as the wheels towed out a large amount. (Although thankfully not nearly as much as when the pin was completely broken.)

I headed over to the opposite side of the tractor to check on the adjuster for the toe-in of the tires. It was a simple turnbuckle mechanism, but had been screwed down tight previously, giving me no chance to observe the threads to see which was a left-hand thread, and which was a right-hand thread.

Grandpa walked over to see what it was about, and we agreed that we needed to undo the linkage from the steering side of things, and then use the entire shaft with a pair of vice grips on it to try to spin the linkage open a bit more. This was very fruitful! We were able to see which side had the left-hand thread, and which had the right, and we ended up dismantling the entire thing, lubing and cleaning it with WD-40, and then re-assembling it with lots of room for adjustment.

Climbing into the tractor seat, I was not a little exhasperated to find a lone, large, flat washer hanging from one of the hydraulic levers. Oh yes, I remember now, it came from between the steering linkage and the top of the wheel casing! I put it there for safe keeping when the tractor first became incapacitated.

I disassembled the top of the wheel assembly once again, inserted this washer, and then reassembled everything. Sigh.

Using the turnbuckle, I adjusted the wheels until they mostly pointed in the same direction, with enough of a hint of toe-in to make me think we were on the right track.

Removing the right wheel, I drained out the remaining hydraulic/transmission/lubricant fluid from the right wheel (via a 20mm bolt on the bottom of the wheel transmission – so to change the fluid on your front axle, there are actually TWO drain plugs that need to be opened). Then, I tried to add a very approximate .8 gallons via the plug on top of the axle. This seemed to fill rapidly, so I would stop regularly, and rock the axle back and forth to even out the fluid levels. I also spun the wheels by hand to get them well coated and push out any air bubbles.

Finally it was seemingly full. With great trepidation I climbed aboard and started her up with a loud, knocking roar. (I want to put on my ear muffs just remembering it!)

I lifted the bucket up, and removed the stump from under the axle where we had left her, low these many weeks. Slowly, I lowered her back onto the wheels, and it held! Of course, the proof was in the pudding. I lifted the bucket further, and then put her into reverse. Slowly releasing the clutch, I actually moved – in reverse! Both wheels moved in the same direction and I was greatly relieved!

Grandpa and I re-examined the toe-in angle, and made a few slight adjustments. For now, we aren’t going to lose sleep over the fact that we aren’t terribly certain if we are within tolerances there, or about the fact that there seems to be a bit of play in the key, so that the wheels can wobble ever so slightly compared to one another. I never take the tractor out of low gear, and it never really drives on pavement, so how much difference can it make? (Please, tell me if it will make a difference – I’d be more than happy to hear opinions.)

I turned her around in front of the vehicles, pondered what would happen if she broke down halfway along our driveway (no answer to that – other than a shudder), and headed down the driveway.

About two thirds of the way, I couldn’t take the pace anymore, and switched from second to third gear (still in low range though), and trotted to the end of our drive. Again, cautiously turning around, trying to stay off the public portion of the road, I headed back triumphantly! I parked her a little further out of the way, and would have done a victory dance, if not for my tremendously sore ankle.

Today it is snowing again. They predict five to ten centimetres. I’m thinking that perhaps I’ll put her to the test if the snow looks that bad. Of course, I’ll have to dig out the now fully buried grader blade, which may be an adventure in itself…

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