by Tyler Buchheit
January 2008
Have you ever felt like the tractor gods were mad at you and your antique tractor? I don’t mean to moan and groan but here lately bad luck (or whatever you call it) has been following me. Two extraordinary events have struck within only a few weeks of each other and both events pertained to 720 John Deere tractors. The first disaster involved my friend, Jonathon, and his 720 gas tractor. It was the first and only tractor where I have seen the crankshaft seize up in person. The second event (or disaster, if you will) involved my 720 diesel dropping the differential drive gear on the countershaft.
Part I: The gas tractor
The shop cleared out quickly as the mechanics punched out from their Saturday at work. While I changed out of my salesman clothes into some that Teresa wouldn’t mind seeing filthy in the wash, Jonathon moved his 720 JD out near the rear of the building to hook up the dynamometer for a ‘break-in’ session. We both had eagerly anticipated the day when we could get the 720 hooked to the dyno and a little bit closer to being ready for painting. Jonathon’s 720 gasoline tractor had just been put back together from what seemed an eternity of parts lying here and there in his compact garage. With only 3.5 hours showing on the hour-meter, we got the dynometer turning at a medium pace.
The hum of the dyno turning and the 720 putt-putt-putting away was music to our ears. After about one-half hour of a light load at 1000 RPMs, we decided to begin varying the load and engine speed. We made some adjustments and looked the tractor over for oil leaks and any funny noises. With nearly 45 minutes of dyno time, I was adjusting the dyno to ever so slightly increase the load on the tractor. Then it happened—the tractor RPMs slowed dramatically, almost like it was running out of fuel, until it came to a dead stop! It happened so fast that we were definitely caught off guard. Not even thinking a horrible thought, I looked at Jonathon with surprise, assuming I had adjusted the dyno too far and made the tractor fall on its face; I instinctively got back up on the tractor to get it started. I pushed down on the starter rod, instantly sticking the starter. Quickly realizing what had occurred, we frantically lifted the seat cushion to get the battery cable loose.
Once we disconnected the battery to hopefully save the starter from melting into one large hunk of useless metal, I put my mind in focus mode. Jonathon suggested that we unhook the dyno and try rolling the tractor in gear to see if the engine would turn over. We tried and tried to get it to budge but to no avail. I found myself running to find another tractor to hook to the 720. I spied a 3020 on the back lot and ran to get on it. What crappy luck that the key wasn’t in it nor did I have my set of JD keys in my pocket. Jonathon was running too and yelling, “Get on the forklift…there are chains in the toolbox.” I jumped on the faithful old JD forklift and sped around the building to get hooked up to the 720.
I put the forklift into fifth gear but it proved too much of a load for it. Jonathon engaged the clutch on the 720 time and time again, but nothing happened except for leaving little reminders around the dealership parking lot in the form of black skid marks from his nearly new 151 Firestone Field and Road tires. Jonathon suggested that he wanted to try turning the engine backwards by engaging it in reverse…still nothing! With no progress made from pulling the tractor, I headed back into the shop with the 720 in tow to regroup and decide what to do next.
We both stood by the tractor still in a state of shock. I was unsure if Jonathon was going to break down and cry or if he was going to throw tools across the shop. After several minutes of silence, I made up my mind that the only way to cope with this situation was to get to work and begin tearing into the tractor to find out why the engine, after only 3.5 hours of run time, had suddenly and unexpectedly seized.
First, we removed the flywheel cover and then noted the temperature on the main bearing housing. We were looking for something hot to indicate a main bearing failure—it felt warm but not too hot to touch. Jonathon also noted that the area around the clutch pulley and reduction gear cover was also at a normal temperature. I suggested that we should at least try and get the crankshaft turning. We proceeded with a pair of large pry bars to turn the flywheel. After some grunting, we got the flywheel to turn a few inches. There were at least some sighs of relief although the crankshaft turning really didn’t prove anything. When our pry points ran out, we opted to look for some seriously heavy pry bars. I spied a few junk combine shafts in the scrap barrel that would do just fine. I inserted the shafts into the two holes in the flywheel while Jonathon pried between them, causing the crankshaft to turn ever so slowly.
About the time we got the crankshaft turned through one revolution, another salesman and a mechanic returned to the shop from a combine delivery. It was probably a good thing they came by as Jonathon wasn’t saying much and appeared to be at his boiling point! We explained what had happened and exchanged several stories about engines blowing up and running wild. After a few good stories, we didn’t feel quite so bad, realizing that at least the 720 didn’t catch fire and become a complete loss.
We decided that taking the tractor home only to once again displace his wife Sabrina’s car from the garage wasn’t the best idea. It was clear that we would have to make some room in the lawn and garden shop area for the 720 nearest to his workbench and tools. The next few hours proved very productive with the crankshaft removed only about 3-1/2 hours after we began. The right hand main bearing had seized right to the crankshaft. We called it quits well past midnight, leaving the tractor over the weekend until Monday.
One downside to having a personal tractor in the shop is that everyone in the building quickly found out what had happened over the weekend. Nearly every mechanic in the shop gave his opinion on what caused the failure. It was clear that something must have gone wrong with the machining of the crankshaft or sizing of the main bearing. Monday morning was a trying day for Jonathon and it took several minutes to explain the situation to the manager of the machine shop where the engine work was done. Everyone finally agreed that we should send the crankshaft back for them to inspect. A few days later, the machine shop called—not willing to admit that faulty machine work was the problem, yet they agreed to fix the crankshaft and size a new bearing free of charge. The only detail that the machinist would agree on is that there was plenty of oil present when the bearing began degrading and seizing to the crankshaft. Jonathon insisted that the machine shop re-size the bearings with more clearance than the JD service manual suggested.
Nearly two weeks after the great disaster, Jonathon and I set out and in just one evening after work, we had his 720 popping once again. At the writing this article, the tractor still runs just fine and we plan once again to put the tractor on the dynometer.
Part II: The diesel…
With the 4th annual River Hills Antique Tractor Club plow day quickly approaching, I finally got coulters installed on my 825 JD roll-over plow and was in a rush to try them out. My father-in-law had offered several acres of his Mississippi River bottom ground for me to practice plowing. I had passed on his offer for the past two years already and didn’t want to pass it up again. I thought that it would be really nice since his farm is about only 15 miles from my house.
I set out on my epic journey on a Thursday afternoon off from work with my 720 and plow. I noticed when pulling onto the highway near my house that the fuel gauge was barely bouncing near the “E.” The needle on the fuel gauge had quit bouncing at all about halfway through my journey so needless to say, there were some tense moments as I pictured where and how I would run out of fuel. After about an hour and 15 minutes, I arrived at the farm near Prairie du Rocher, Illinois. I pulled directly up to the fuel tank when I arrived and I quickly inspected the tank with a very dry bottom.
My father-in-law watched intently as I set out near his machine shed laying a neat furrow down through the rich black bottomland. I made several adjustments on the plow, leveling the hitch here and there until it was set just about right. Daylight was just about all gone when I managed to get Marvin onto the 720. He hadn’t plowed in the open in quite some time. Normally a modern “red” tractor driver, Marvin looked a little out of character driving my 720 John Deere. I will give him credit though—for someone not familiar with a hand clutch, he did very well with the tractor. With only a few acres yet to plow (he had left me a small five or six acre strip in the field that he didn’t already chisel-plow), we decided to park the tractor for another day.
After eating a hearty chicken and dumpling dinner at the local Legion Post, I set out for a Sunday afternoon plow to finish up the job I had begun a few days earlier. The soil was working superbly—turning over easily and not too dry or sticky. I plugged away at the field until only a few passes remained. On my return trip down the field, I began noticing a noise like brake chatter through my foam earplugs (you’ve got to wear them if you want to save the hearing you have left). I didn’t think too much of the noise until a few yards farther when it once again caught my attention. I stopped and down shifted into third gear, thinking that maybe the clutch was slipping. Changing gears didn’t seem to help as the noise got progressively worse. Finally, the noise was accompanied by jerking and gear noise. It was then that I decided to limp it back to the machine shed in first gear. This solution worked for a bit until the tractor suddenly quit moving. I tried a few more gears and finally got the machine to move in reverse. I drove the tractor in front of the machine shed in reverse (without any unusual gear noise) and shut it off.
I was dismayed to even begin thinking that my transmission was junk! With no suitable trailer at the farm to help haul the tractor back to my own shop, I reluctantly made my way across the river to Dad’s farm in Missouri to retrieve his truck and trailer. I called Jonathon along the way to tell him about my “great” news. He couldn’t believe that now my tractor was having problems. He agreed to meet me at my house (remember this is Sunday night and we both had to be at work Monday morning) to help tear into the tractor.
So we began the tear down project late into Sunday evening. Jonathon took the clutch side of the tractor as he was an expert, having recently done the same job on his 720 only a few weeks prior. I took the task of removing the flywheel and timing gear cover on the left hand side of the tractor. Everything was going smooth until I finally got stuck trying to remove the flywheel from the crankshaft. I recalled that I had to take an eight by eight oak block and a sledge hammer to install it a year earlier when I rebuilt the engine. The flywheel took us nearly 45 minutes to remove! It seems that I did not have a loose flywheel problem as many JD owners realize so well, but rather a tight flywheel.
We finally got the top cover off and tried to see what was wrong inside the transmission but were unable to see any problems. The shift shafts and top shaft appeared OK so we kept digging deeper into the transmission. With the top shaft and sliding gears out, it was clear what had happened. I’ve found that you feel sick when the transmission you personally rebuilt has catastrophic failure, but when the cause of the problem is improper installation procedure by the owner of the tractor, it only adds to the shame! It turned out that the differential drive pinion and the spacer between it and the second and fifth gear were switched. The result of this mistake was that the tractor had been run at 40 hours with a differential drive pinion that was contacting the differential ring pinion by only one-eighth of an inch! At just slightly after 12:30 a.m. on Monday, we called it quits and headed for a few hours of sleep before going to work.
My brother, Alex, and I did the transmission installation a little over a year before the failure and I still can’t accept that both of us could have done something so obviously incorrect! Whether he or I installed the gears incorrectly, we were both there at the same time and we can’t fix history. I made a phone call first thing on Monday morning and ordered what could possibly be the last new F2613R pinion gear in existence from a JD dealer in New Hampshire. Thanks to my brother’s help, we were able to nearly complete the reassembly on the flywheel side and only have the reduction cover and clutch to go before plow day (one day away). I will be sure to inform you the outcome with plow day.
Now you know that the Youngtimer might be smart at times but also human in that mistakes can and will happen. The good news is that my tractor is repairable with new parts. I hope and pray that there will be no more tractor surprises for at least the foreseeable future. I can say the same for Jonathon and that we hope to never again see this deep inside our tractors again for the rest of our lives! Until next time and hopefully no more bad luck!
