Regardless of whether your antique iron is a hobby tractor or still earning its keep on the farm, the one thing we can all agree on is the trepidation about whether or not the engine will start, especially on a colder day.
We have all endured the frustration of needing to get a chore done on the farm, only to be sidelined by an ornery tractor refusing to run. Or you travel to a show or parade, and you suffer the embarrassment of your beautifully restored machine being indignant about leaving the trailer.
An event such as that quickly establishes the thin veil between love and hate that an old tractor can reveal. Growing up with a Hart-Parr Oliver Row Crop 70 on our place, I quickly learned why my dad always parked that powerful machine on the hill in the apple orchard by our house. She never failed to run after a high-gear pop start.
But unfortunately, that could not be said about the electric start, which sometimes was less effective than the hand crank. At ten years- old, I did not have the oats to turn the engine over with the hand crank, but the truth be told, I had the finesse that defied my young age, to slip the clutch just right as the Oliver rolled down the hill.
The quest to get your tractor to start quickly can require a multifaceted approach rooted in isolating and then eliminating each reason why it does not. In most instances, the hard starting is rooted in more than one area. For this reason, each will be discussed separately.
Where it all begins
For the engine to start, the cranking motor (the proper name for the starter) needs to rotate the crankshaft fast enough to draw the air/fuel mixture into the cylinders. This must be accomplished while the battery has sufficient potential energy to provide the ignition system with enough voltage to create a powerful arc to jump the spark plug gap under compression.
At the same time, the created air/fuel mixture needs to be of the proper ratio to ignite. The initiation of the spark plug arcing must occur at the required position of the piston as it travels in the cylinder.
When all this happens with the precision of a Special Forces operation, the tractor engine starts immediately. However, if one aspect of this chain of events is off, then the engine will either be hard starting or will not run at all.
When diagnosing a hard-starting problem, it must be thought of as one looks at soil fertility. When reviewing a soil test, the first thing you look at is PH. If the PH is off, then some of the other nutrients already present may not be available for the plant.
The most important thing is the chain of events in starting the engine is cranking speed. If that is too low, then as with soil, some of the other necessary actions will become skewed and compound the poor cranking speed. So, the first place you need to explore is cranking speed.
The cranking speed of the engine will depend on the following areas that all need to be checked.
Battery voltage and condition, the integrity of the battery cables and their load carry capacity, internal friction and amperage draw of the starter motor, state of the ground circuit, the ignition timing setting, the thickness of the engine oil, and internal engine friction.
The tractors that generally have the most issues with creating a sufficient cranking speed are designed around a 6-volt battery. Though a battery of this rating does not have the additional capacity to make up for any weakness in any other area of the cranking system, it must be recognized that it started quickly when the tractor was new. Thus, something has changed over the years.
From my experience, most owners are good about replacing the battery with a new one. Still, they are negligent in examining the internal workings of the cranking motor, the condition and size of the battery cables, and the integrity of the ground circuit.
A rule that I like to apply is if the battery is new and the cranking speed is borderline, then the cranking motor and cables are the issue. But let me divest for a moment.
Any electrical device functions on the criteria of Ohms law. Even if the cranking speed is acceptable, if the voltage drop through the cables is too high or the current demand of the starter is excessive, it steals potential energy from the ignition coil, which results in a spark that is not strong enough to create combustion.
For this reason, it is prudent to check the voltage to the ignition coil with a meter at the lead from the ignition switch, when the engine is being cranked. With a good battery and companion components, the power to the coil should be near battery voltage. If it is not, the starter, cables or ground are causing the drop.
Many tractor owners are misled by an engine that sounds as if it is cranking well, and it may be. Still, due to inefficiencies, it consumes an excessive amount of energy from the battery. The result is an engine that is hard to start, and fuel fouls the spark plugs easily.
The starter needs to be taken to and shop bench tested to alleviate this problem. You will usually find it dirty inside; the brushes being worn along with the bushing that the armature spins in.
The next thing to look at is the battery cables and connections. The best thing to do is just replace them since you cannot see inside. Over the years, corrosion sneaks in between the wire and the insulation.
I suggest getting some length of “OO” gauge cable and either make up your own leads or speak with one of the many companies that make custom leads and have them professionally install the proper ends. If you have a good 6-volt battery, an efficient starter, heavy cables with good ends, and a clean ground, the engine will crank almost as well as if you did a 12-volt conversion.
Once the cranking circuit is up to standard, you can now check the voltage to the coil during the engine crank, and if it is still low, the problem is from the ignition switch to the coil.
Another area to check is the ignition timing with a timing light. I am always amazed at how many tractor owners time the engine “by ear.” Due to the burn characteristics of modern fuel, you can only use the factory specification as a starting point for the base timing.
Try settings a few degrees different from the specification and see how it starts and runs. Find a balance between proper starting and good engine performance.
Also, check the centrifugal advance curve. I have seen tractor distributors/magnetos with broken advance weight springs. When the timing is being checked, full advance is already in. The owner resets the timing, and now during crank, the arcing of the spark plugs is too late, and the engine is hard to start.
The mixture will be too lean to ignite if the engine has a manifold vacuum leak. In addition, the excessive amount of cranking will weaken the battery and starve a sound ignition system of voltage. This now becomes a merry-go-round. The problem is a lean mixture but presents an ignition concern because the excessive cranking caused the spark plugs to get wet.
It needs to be remembered that a mixture that is too lean to ignite will still wet the spark plugs, if the engine does not fire. It is a lean mixture in ratio and should not be interpreted as no fuel, it is not enough fuel for the engine to run.
Even though a proper 6-volt system will start the engine fine when all else is up to standards, a little reserve never hurt anyone. For this reason, I use an 8-volt battery in my 1940 Ford 9N.
On many older tractors, such as the 9N, you can turn up the charging voltage on the generator with a screw. Then, run the engine at fast idle with a voltmeter across the battery terminals and, if applicable, make the charging voltage adjustment.
I set mine for around 9.2 volts which keeps the 8-volt battery fully charged. Though the 9N started almost immediately during the 43 years it has lived with us, it is happier with the 8-volt battery. There simply is more reserve due to the extra cell in the battery.
In closing, if you get the engine to crank fast enough and all aspects of the ignition and fuel delivery are correct, though there is certainly nothing wrong with a 12-volt/alternator conversion, you can enjoy the bragging rights of keeping it all factory.
As God and the tractor manufacturer intended!