No, this isn't about the Kennedy assassination, nor is it about grass or even a knoll. “Grass knoll” sounds like “glass bowl,” which is a term that columnist Gene Weingarten used to describe a part of his character that causes him to be rude in public. “Glass bowl” rhymes with a phrase that bystanders use during these events. Since Gene has already laid claim to “glass bowl,” I'll use “grass knoll” in the same manner to describe the subdued sounds made by some mechanics when a customer insists upon watching a repair “to see how it's done.”

Not that the customer's presence is any real problem. In fact, there are those who I would gladly invite to be present. In general, experienced mechanics can function on two levels, making the repair and making conversation, at the same time. Just don't quiz the mechanic on the conversation afterward.

When I consider what the “grass knoll” customer is demanding, I must concede that this customer may have been misled to believe that he can absorb the benefit of decades of experience and study in an afternoon. Many mechanics may be a little challenged in the diction and eloquence department, leading the customer to believe there's not much going on upstairs—rest assured that there is. When that gnarled geezer with two days of white stubble and breath like a stale carburetor listens to your engine and says “Peckin' purty bad, ain't she?” he speaks from a clear understanding of hydraulics, physics, fluid dynamics, and metallurgy. They just don't hand out college degrees in these subjects in places like Toadwheel, West Virginia.

In fact, mechanics steward some very complex and awesome forces. Anyone who has ever felt the thunderbolt discharge of an old tractor magneto is likely to agree. This unique experience is caused by the buildup and collapse of a magnetic field in an ignition coil that turns a tiny flow of electricity or, in some cases, simple motion into a sudden high voltage jolt. Why? Because the One who made this planet said so. (It is seldom profitable, in the long run, to test the limits of his laws and principles. Doing so can result in electrical shock, injuries from falls [law of gravity], plague, unwanted pregnancy, and DUI charges.)

My favorite demonstration of this principle occurred when charged particles from the Aurora Borealis slipped into the Canadian countryside and surrounded a remote section of high voltage power line, creating a magnetic field around it. The particles withdrew and the magnetic field collapsed. This sent a charge of astronomical voltage into the grid, blacking out parts of Canada and the U.S., including New York City. Many of us have no trouble imagining a colossal Delco ignition coil nestled in the boreal forest having the same effect.

Fuel is injected into a diesel engine at pressures that exceed 1000 pounds per square inch. The grizzly possibility exists for anyone in close proximity to a diesel engine undergoing repair of being hit by this stream. At those pressures, the fuel stream can easily penetrate the skin and pump the unfortunate appendage full of diesel fuel. Not the sort of tattoo that you would care to have, I might guess. One grass knoller suggested that much trouble and expense could be avoided and much less safety compromised if this pressure were lowered.

These pressures are necessary to overcome the pressures of compression ignition. Imagine that our universe were suddenly compressed to a much smaller size. Our year would be dramatically shortened, and everything would move faster until irritating things like Christmas and in-law visits would be happening many times a day. We would protest in a civilized manner by writing letters to our editors and seeking an act of Congress for relief and compensation.

Air consists of ignorant atoms and molecules that, when crowded and hurried and having no other way of expressing themselves, simply (unlike us) become heated and agitated. Fuel is injected into this molecular donnybrook, which normally reaches temperatures of 1600 degrees Fahrenheit. In this way, the diesel engine resembles its distant cousin, the atomic bomb.

It has been theorized that there exists a bazillion to one chance that a man-made nuclear event could touch off a chain reaction that would destroy all matter on earth. The probability of your hopping on your Kubota to mow the lawn and ending civilization instead doesn't loom very large. Still it does make a good case for keeping your diesel tractor's air cleaner in good repair, lest the engine up the odds by ingesting any plutonium dust that may be lying around the place.

Well, the foregoing touches on some of the technical highlights of my day job. I've kept it limited to the ignition system, but there is much more; don't even get me started on hydraulics. If you want to look over your mechanic's shoulder and understand “how it's done,” read up on some of the principles involved. Don't become a glass bowl or grass knoll which rhymes with . . . well, you get the idea.

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