Refurbishing An Old Gas Tractor

This is a continuation of our series on Cultivator Tractors

Written by Joseph M Hannan , Production Instructor 
Center for Arkansas Farms and Food 
04.30.2025

Edited by Luke Freeman

Bringing the tractor home

What does it take to get an old cultivator tractor up and running for daily use?

You have now purchased a used cultivator tractor. Congratulations on owning a 30- to 60-year-old piece of equipment with questionable electronics, service (hahaha what service), and expect to base your livelihood on this piece of equipment functioning 7 days a week for 10 months of the year. Regardless of the claimed condition at purchase, it would be wise to take some time during the off-season and really inspect and replace known and expected wear parts. Finding and replacing parts during the off season is much easier and less stressful than during the growing season. (Been there…done that…don’t do that!)

Let’s start off by saying I am expecting that you purchased something at least in running condition. There are enough options out there that there is no reason not too!

As soon as you purchase the tractor, find an owner’s manual as well as a service or repair manual. These books are incredibly helpful as you service and maintain your tractors and are available from a variety of vendors online and brick and mortar farm stores.

After you get your “new” tractor home, first and foremost, start with a quick check and top off of all fluids (oil, hydraulic, and coolant), clean the air filter, check the fuel filter or fuel sediment bowl, and check any belts on the generator/alternator and fan. At this point, you are NOT changing fluids and filters, you just want to ensure the tractor can be safely operated before further testing. Next, power wash and decrease the entire tractor. A foaming cannon with soap and degreaser is a must!   Remove as much oil and dirt residue as possible.  This will make it easier to service the tractor later and identify any oil leaks. Finally, hook the tractor up to an implement, preferably something ground engaging, and go till a field for an hour or so. The goal here is to get the tractor and fluids warm. Often, fluids won’t start to leak until they warm up and thin down a bit. By working the tractor, you will find leaks that don’t occur when just parked but do occur when the tractor is actually being used in the field. At the same time, check all lights, verify all gauges are working, test all gears, brakes, clutch, and all hydraulics.

Now is the time to identify any and all issues and construct a list of what needs to be repaired and what needs to be monitored.  Most issues are not difficult to fix but require a significant investment in time for disassembly and reassembly such that questionable parts, seals, etc, should be replaced when you have access for any unrelated repair.

At this stage of identifying repair and maintenance issues, it’s a good time to remind yourself that you purchased a business expense, not a collector’s item. It is unrealistic to keep your daily workhorse in factory original quality with factory original parts. After 30 to 60 years, there are places where upgrades make sense, while keeping the tractor operating within its designed specifications. The goal should be reliability!

Let’s go through some core components piece by piece

Gas Tractor Electrical System

For the electrical system, first start by determining if you have a 6V generator, 12V generator, or 12V alternator. This is the system that creates a charge for the spark plugs and charges the battery. Unless you are going to do a complete changeover from alternator to battery to control panel, to starter, and everything else, it is critical to know if you have a 6v or 12 volt system as parts between the two are not interchangeable. Do NOT just look at the battery voltage as that assumes the previous owner didn’t mess something up. You really need to test the power coming off the generator. Generators will be large cylindrical tubes with a pully on one end connected to the front of the motor and wires coming out the opposite end. A generator creates electrical power, similar to an alternator. In general, for 6V systems, the positive side of the battery will be grounded (connected) to the tractor frame while the negative side of the battery is feeding the starter and lights. This is backwards to most automotive electrical systems. 6 volt generators will also be labeled as 6V. However, that assumes the label is correct and is not missing. You can test power with a volt meter coming out of the alternator, at the regulator box, to see if you have 6V or 12V power. Most 12V generator and alternator systems will operate with the negative battery terminal grounded (connected) to the tractor frame, as found on most modern vehicles.

Once you know the type of electrical system, check the date on the battery. If it is more than 4 years old, replace it. If it less than 4 years old or you are not sure of the age, remove the battery and take it to an automotive store for testing. They can tell you if the battery is good or not. Realistically, just replace it! While you are working on the battery, now is a good time to replace the large ground and starter cables that connect to the battery. These cable can look fine and even test as functional when the tractor is off or running at idle. But, when put under load, if the cables are internally rotted or rusted, they may not actually function under load. Don’t ask me how long I spent chasing electrical gremlins for this problem this past year at CAFF or you are bound to receive a vicious death glare (the type your cat gives you when you have been at the farm working too much!).

Once the battery and cables are replaced, use a volt meter, set to DC voltage, to test ground and positive connections. For ground voltage, place the positive volt meter probe on the battery and the negative prove on the grounding bolt (the location where the battery ground cable connects to the tractor frame). For the positive voltage, place the positive volt meter probe on the battery and the negative probe on the large wire on the starter. On a diesel tractor you should have live power to the starter and have a voltage reading. On a gasoline tractor, you may need to engage the starter with the switch on the counsel to get a voltage reading. Regardless of gas vs diesel, if you have good connections, you should have the same voltage at each testing location as the battery. If you don’t you have a poor connection somewhere. Recheck all connections and test again.  It is absolutely critical that you have excellent connections everywhere or you WILL have to deal with electrical gremlins during the season!

You can test the alternator by using a volt meter, again set to measure DC voltage, on the battery while the tractor is off. Put the positive lead on the positive battery terminal and the negative lead on the negative terminal. The voltage should be 12.4 to 12.8 volts if the battery is fully charged. Next, start the tractor, rev up the RPM’s to 1/3 throttle and retest the voltage on the battery. If you don’t see a voltage increase now that the tractor is running, either the generator/alternator is not working, the voltage regulator is not working, or you have a poor connection somewhere. First, check and clean all wire connections between the alternator and the battery. Next, remove the generator/alternator and bench test it. To bench test, apply power to the armature. If the generator/alternator spins, it is probably working. If not, take it to a professional and have them inspect and rebuild as necessary. However, if your tractor has a generator, it may be just as reasonable to simply upgrade to a single wire or three wire alternator. If you go to a single wire alternator, you can also remove the voltage regulator. If the generator and wire connections all check out, voltage regulators are only about $35 to replace and would be the final check for the system not generating a charge.

The final, general electric tip for all tractors, is to go through and clean all wire connections, replace wires as necessary, and track voltage through the system to ensure you have continuous power flow. When checking voltage, if you see any drop off in power through the system, you have a bad connection!

A simple reality check here: Replace the battery, positive and negative terminals, generator/starter, and all wiring.

At this point, pun intended, remove the distributor cap and clean the points. The distributor is responsible for sending the electrical charge to each spark plug, at the correct time. When you open up the distributor, there should be a cap, a spacer, and then the points. When points get rusty and fouled up, the electrical connection is broken and the spark plugs won’t receive a charge. Clean the points with 400 grit sandpaper or an emery board. Points are a wear item and eventually need to be replaced. Inside the distributor you will also find a condenser and rotor. An ignition tune up kit will replace all three of these items. Its not a bad idea to replace them and will only cost a few hours and $100 or so.

You are now ready for spark plugs, plug wires, and a new coil. A full ignition tune up kit will often contain all of these items. Again, $100 and a few hours to do!

At minimum, a full ignition tune-up kit is essential. However, it really is not that expensive or challenging to do a complete rewire on a gasoline tractor. I just did our Farmall 140 at CAFF this past summer. This would include

• 12V alternator, single wire (or completely rebuild your 12V generator)
• 12V starter (replace or full rebuild)
• All new wire including ground, starter, charge (from alternator), power supply to condenser, spark plug wires
• Spark plugs, coil pack, points, condenser, and rotor
• Electrical charge gauge
• Key switch
• Starter button
• Battery

Total cost of everything excluding points and condenser, was about $1000 and about 6 to 8 hours of labor. I probably spent 16 hours diagnosing and chasing gremlins…I would have been way ahead to just do the rebuild. Do not skimp on the alternator replacement or generator rebuild and the starter rebuild/replacement. After 40 plus years, they have probably had a partial rebuild but for daily reliability, you really do need to do a full rebuild or replacement. The cost for those two items is about $500 so half the cost of the entire electrical system rebuild. We purchased new items but I do intend to go back and rebuild the old ones and have them on-hand in case they are needed. If you don’t replace them now, at least be prepared to do so in the near future.

Let’s move onto the fuel system.

Gas Fuel System

Gasoline tractors need fuel, air, and spark to run.  Gasoline tractors have a carburetor that controls the air and fuel ratio. It is safe to assume that the carburetor needs to be rebuilt. Jets and floats get plugged, worn, and sticky as they age which greatly reduces drivability. You should not have to replace the carburetor as there are generally full rebuild kits available. However, don’t assume that the carburetor currently on the tractor is the original one to the tractor. Make sure you check the specific carburetor and get the appropriate full rebuild kit. Carburetor rebuilds are not exactly fun to do, but essential for everyday reliability. Before adding fuel back to the carburetor, be sure to clean the fuel tank and fuel filter. Metal fuel tanks can get rusty inside and start shedding rust flakes that clog up the carburetor jets. If this is the case, add an in-line fuel filter to ensure any debris in the gasoline tank does not make its way to the carburetor. There are sealants and strategies for dealing with rusty tanks. Electrolysis may be the simplest from my perspective but others will strongly suggest liners.

Be sure to only use non-ethanol gasoline and consider a fuel additive such as SeaFoam to help keep the gasoline dry (free of water) if the tractor isn’t used often.

The carburetor may also need adjustment to set idle, especially after a rebuild or replacement. Your manual should have directions on how to do this. One note though, usually you need a working Tachometer to get it set correctly…but the tachometer cables are often broken and need replacement.

Finally, the older gasolines engines will likely have an oil bath air filter that will need to be serviced. If you are lucky, you can get by with just dumping the old oil and replacing with new engine oil. Worse case, you also need to replace the metal mesh inside.

Fluids

Now onto the messy part, changing all the fluids and filters. For all fluids and filters, soak the drain plugs and fill plugs with your favorite penetrating oil for a few days to get things loosened up. It may have been awhile since these plugs were removed!

First up is engine oil and filter as it is the easiest. On the Farmall 140, there is a main drain plug underneath and a fill plug on the front passenger side of the motor. The filter could either be a spin on type or a filter cartridge (filter inside a metal container). Most tractors came with the filter cartridge but they may have been upgraded to a spin on type. Upgrading to a spin on type is not a bad idea as they should leak less than the cartridge type.

The rear drive train fluid should also be drained and replaced. I cannot speak for other brands, but for International, it is a good idea to go with 80w90 gear oil. This is heavier than recommended in the manual but International tractors can have a bit of a gear wine with lighter oil. The heavier oil helps keep things quiet-ish.

While you are in the rear of the tractor, the drop axles have oil as well. I think, in most cases, the only way to drain the drop axles is to disassemble them, clean them, then reinstall with new gaskets and oil. That’s a major job and probably not something I would get into until I needed to replace gears or bearing inside the drop axles. At CAFF, Ari used a small pump to extract the old fluid through the fill port, then pumped in new fluid. The pump was a $10 pump I purchased from Amazon. It was slow but far easier than a complete rear drop axle disassembly. Warning: it takes a lot of oil to replace the rear drive train and drop axles.

The steering box, located on the front passenger side has a drain and fill port for fresh oil. On the Farmall 140, it can be difficult to get the fill plug removed and reinstalled due to the engine side cover. The fill plug comes out and goes back in without removing the engine side cover, but it was a challenge.

The coolant in the radiator is easy to drain and refill. I believe the drain plug is on the lower driver side of the radiator. Note that there is no auxiliary coolant tank so any overfill will come out on its own. You may want to drain and flush the radiator (with the tractor running and a hose going into the top of the radiator) to remove any build up or debris inside the radiator that may reduce cooling effectiveness. I generally refill the radiator with 50/50 coolant/distilled water mix. 1) its easy to mix and 2) its good for temperatures down to about -20…colder than we should experience in Arkansas.

On a Farmall 140, the hydraulic oil and transmission oil are separate fluids (well same fluid but in two separate containers). There are a couple of drain ports, a fill port, and a top off port for the transmission fluid on the Farmall 140. I don’t believe there is any filter for this system…just dump the fluid and replace with fresh. In fact, the 140 is a bit different than the diesel tractors which all have one fluid and one drain for hydraulic, transmission, and rear drive train.

Finally, the Touch Control, or hydraulic fluid, needs to be replaced…at least on the Farmall 140. This fluid controls the mid-mount and rear cultivator raise and lower actuation. This fluid needs to be drained AND there is an internal filter that needs to be removed, cleaned, and reinstalled. Refill the fluid up to the top of the fill spout, start the tractor, and then actuate the Touch Controls for the rear and mid mount arms to work out any air bubbles. Top off the fill spout as needed. Continue until all air bubbles are out.  Its kind of a pain! That said, the Touch Control box and valves are probably due for a rebuild. This box and valves MUST work or you cannot raise and lower your cultivators. Rebuild kits are available but it’s a big job to remove the fuel tank and all of the hydraulic components to get at the box to do the rebuild. Before doing this, try to just dump the old fluid and clean the filter…maybe you will get lucky and not have to do the rebuild for awhile. CAFF unfortunately isn’t so lucky…and ours has serious problems.

Other Items

Other things to check and adjust include the brakes, clutch pedal, and fan belt. Some of these items may need to be serviced, some may not.

You should also look around the tractor for any major fluid leaks…you may be able to just tighten a loose bolt up to stop or slow a leak or you may need to do a full gasket replacement. On a 40 to 60 year old tractor, you are going to have some leakage. Old tractors leaking fluids is right up there in certainty as death and taxes. Keep an eye on things and repair or top off fluids as necessary.

Be sure to check the tires for excessive weather checking and rim rot. If the wheels are fluid filled, the rims could be rotting away. Replace as needed.

Finally, I did not dive into doing full on engine, drivetrain, or clutch rebuilds at this stage. I guess I would consider a tractor non-working if it had those issues at time of purchase and would look elsewhere unless you had the skills to do that work…

Gas Tractor Summary

Getting an old gasoline cultivator tractor running, reliably, takes some time and work. The key on an old Farmall 140 is the electrical system, carburetor, and fluids. Service those items and you are likely in pretty good shape unless the tractor has serious repairs that are needed. Seriously…just replace the entire electrical system. Upgrade to a 12v alternator and all new wire and batteries! Save yourself some headache chasing gremlins later. Also go ahead and plan to rebuild the touch control. It is not a fun job but it probably needs it!