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By Root 309 0

is difficult to say where careful assembly ends and blue printing begins, since rebuilding old motors involves lots of measuring and judging to begin with. The wear of each part must be determined so you can calculate whether tolerances are within spec. This involves visual inspection as well as measuring; the skills of an engine builder are in good part forensic. After some time in the solvent tank and some elbow grease, followed by hot soapy water, the internals of the torn-down motor were spotlessly clean. Chas then looked for signs of galling and discoloration that would indicate excessive heat, hence inadequate lubrication, or some other source of unacceptable friction. In fact there was some galling on the cam lobes, and the task now was to identify the root cause.

Root causes manifest as coherent patterns of wear, and knowledge of these patterns disciplines the perception of an engine builder; his attentiveness has a certain direction to it. He is not just passively receptive to data, but actively seeks it out. Pursuing one hypothesis, Chas looked for mushrooming at the tips of the valve stems, which bear on the cam lobes via rocker arms, push rods, and lifters. Sure enough, some of the valve stems were slightly bulged out at their tips. Previously, as we were cleaning parts, I had held one of these valves in my hand and examined it naïvely, but had not noticed the mushrooming. Now I saw it. Countless times since that day, a more experienced mechanic has pointed out to me something that was right in front of my face, but which I lacked the knowledge to see. It is an uncanny experience; the raw sensual data reaching my eye before and after are the same, but without the pertinent framework of meaning, the features in question are invisible. Once they have been pointed out, it seems impossible that I should not have seen them before.

This weird aspect of perception was brought home to me twenty years later in a drawing class, and the parallels between mechanical perception and drawing merit a digression here. The teacher of the class, who happened to be my shop mate and fellow motorcycle mechanic Tommy, brought a human skeleton for us to draw. I drew what could only be described as a Halloween display such as you might see at Walgreens. I had seen images of skeletons since I was a little kid, and try as I might to represent the skeleton before me, I drew an icon of the thing rather than the thing itself. To actually reproduce the pattern of light hitting your eye with a pencil seems like it should be a straightforward matter, but it is extraordinarily difficult. It seems to require that you short-circuit your normal mode of perception, which is less data-driven than concept-driven. We have an idea of the thing that, in a sense, pre-constitutes the thing for us, prior to sensual experience.

In a sort of empiricist shock therapy, Tommy turned the skeleton so that we were viewing it end-on, with the pelvis toward us. Now we were viewing it in a completely unaccustomed perspective, with most of its familiar features foreshortened or obscured. But those features were still present in my mind, and because they were now so completely inappropriate to the way the skeleton was actually presenting itself to me, their interference in my attempt to draw what I saw became more obvious, an object of attention. Trying to draw the skeleton end-on required going back and forth: first a critical attention by which I tried to be aware of, and hold in abeyance, my prior Hal-loween skeleton, then trying to attend to the visual data more directly. But the latter activity was like trying to bushwhack through a thick undergrowth of perception, with no apparent way forward to comprehension. Lines and planes were not clearly distinguishable in the jumble of bones, nor was there an evident logic of function such as you see in a skeleton as normally viewed, or in the framing of a house before the sheathing is nailed up. It wasn’t so much that it felt like there was too much information, but rather that what I saw was ambiguous, unstructured,