The old barn find is finally running and sounds just like an old tractor — a 2-cylinder John Deere. But it’s not a 2-cylinder John Deere. One or more cylinders aren’t firing. Let’s leave it running, though, as we chase down the culprit. If, as is often the case, the ignition wire connectors are uninsulated on the sparkplug end, we need only to ground each one with a screwdriver and listen for a corresponding change in the sound of the engine. No change means that the cylinder is not firing.
It’s important to remember not to use a screwdriver with metal exposed in the handle or to touch the metal part of the tool during the procedure. If we forget, we won’t need to be reminded again. If the connections are insulated, it’s time to find that electrician’s fuse puller that we used a while back to test for the presence of spark.
With the engine running, slowly pull and replace the wires from the sparkplugs one at a time while listening carefully for any change in the sound of the engine. If, for a moment, the engine smoothes out while the wire is being removed or replaced, the spark plug is fouled. This problem is quite common since, as discussed in an earlier installment, barn find plugs are usually of too cold a heat range. The “dead” cylinders located with the screwdriver can be tested in this manner as well. If no spark is detected visually or audibly (the electric arc makes a clicking sound), then the wire itself is likely at fault.
Why a fouled plug often fires when the wire is held a distance away from the plug is a mystery to me — I just know that it works. I first saw this method applied when Uncle Victor got an old Oliver dozer running when no one else could by somehow spacing the wires from the plugs. (See the story “Getting Out and Looking In.”)
When my father and uncles left the farm for careers in manufacturing, they more or less abandoned the farm’s workshop to us curious youngsters. The old dirt floor shop had been used by our family to repair all sorts of farm machinery, trucks and personal vehicles since around 1930. It was where my dad left his 1932 Ford Coupe during World War II and returned from Germany to find that one of his brothers had converted it into a roadster.
The corners and the space under the workbench were full of mysterious antiquities of the golden age of progress — strange updraft carburetors, wooden boxed coils, massive piston and connecting rod assemblies. Among this collection were several well worn Llyod non-fouling spark plugs with their bold slogan “Fires in Oil!” enameled on their, porcelain insulators. This plug used this same principle of creating an arc between the wire and the sparkplug electrode.
Would these plugs actually fire while submerged in oil? I don’t know, but I can imagine a fellow writer known for his scientific approach conducted the experiment: “Only by using a 50-pound Tesla coil was I able to create the required 6 million megavolts and cause the plug to arc while submerged in a bowl of period correct straight 30 weight oil on my kitchen table. This, in turn, set of an explosion that ignited the gasoline experiment in my freezer and caramelized the antifreeze experiment in my sink. I followed with a comparison test of halon and carbon tetrachloride fire extinguishers.”
The diesel version of this diagnostic procedure is similar, in principle anyway. The basic idea of intentionally disabling each cylinder in turn still applies. Though the danger of electric shock is virtually nonexistent, the grisly prospect of being injected with a 1,000 PSI stream of diesel fuel realistically looms. This fuel would then have to be excised surgically.
If a diesel engine is missing due to low compression (a valve out of adjustment if we’re lucky), there will be excessive smoke. This smoke usually appears white or blue if the cylinder is almost firing and the fuel droplets are thus singed. This blue smoke will appear brown in artificial light or above around 48 degrees North latitude, according to a reader from near the Canadian border.
With the engine running, follow the fuel lines from the injector pump to the injectors and slightly loosen the line at the injector. Fuel should then spurt from around the fitting, reducing the fuel pressure to the point that it is not adequate to open the injector, thereby disabling the cylinder.
Again, listen for a change in the sound of the engine and observe whether this causes more vibration. No change means that the cylinder isn’t firing. If there has been a lot of white smoke present and the cylinder isn’t firing, observe whether the smoke disappears during the procedure. This will indicate that the cylinder is missing due to low compression.
Tractors equipped with GM Detroit diesel engines such as the John Deere 435D, 4401D, Oliver Super99GM and its Massey Ferguson counterpart require a different procedure unique to these engines. This ingenious 2-stroke diesel was in production from the ’30s to nearly the end of that century. There is consequently no shortage of GM Detroit “experts” around but you might start with the local retirement home.
First published June 10, 2015, based on a column in Antique Power magazine published in 2013.