The parts
Let's take apart the camshaft. Cam lobes--the "bumps" if you please--are really fascinating! The lobe is not just an ellipse machined onto a shaft. It's actually a complex shape with several distinct zones, each with its own function. Let's start with the lobe's "base circle", also called the heel. This is that part of the cam lobe that looks mostly perfectly round (though it isn't always), a constant radius. It's the datum line, the point of departure from which everything else on the lobe is measured. It is also the valve's fully-closed area, giving the valve its cooling time. Opposite the cam's base circle is the "nose", the point at which the valve is fully open. The nose affects valve open spring pressure and enters into part interference issues, both important considerations in engine building. On either side of the nose are very steep areas called "flanks". They open and close the valve. On some cams the opening and closing flanks are symmetrical. But not on all of them. In addition, shim type engines, rocker arm engines, and pushrod engines each have their own distinct flank shapes, some flattish but many very rounded. Rocker arm engines have assymetrical cam lobes. As the cam lobe rolls beneath the rocker arm's pad, the leverage ratio of the rocker arm changes slightly, resulting in a difference between the valve's opening and closing speeds. To compensate, cams for rocker arm engines have lobes whose opening and closing flanks are very differently shaped. Engines with roller rockers have cams that are much less pointy, more like a lemon than an egg in profile.

The ramp
But the most interesting of all the cam lobe's parts and one with many secrets is the "ramp". So small as to be detectable only with a dial indicator, the ramp is the transition from the radius of the base circle to the broad surface of the flank. For just a handful of crankshaft degrees, the ramp cushions the valve to prevent its opening and closing too abruptly. This really matters when the valve moves hundreds of times a second. There are of course ramps on both the opening and closing sides of the lobe. What is little known to those other than engine builders is that these ramps determine valve clearance. A specified valve clearance is solely a product of the camshaft's ramps. The more ramp a cam has, the less valve clearance the engine needs. And vice versa.

Compensation
Paradoxically, there isn't actually room enough on the cam lobe for as much transition as the valve needs, as much ramp in other words. Valve clearance actually supplements the ramp's built-in cushion. Different motorcycles have different valve clearance specifications because they have different cams with different amounts of ramp. Modern engines run three to five times the valve clearance of engines of fifty years ago simply because the huge lobes on their higher-output engines' cams lobes cut into the ramps (only so much real estate in a circle), making them smaller.

Valve clearance
Many folks seem to believe that should an engine develop a slight ticking noise this means the valves are out of adjustment. Actually, there is little direct connection between sound and correct clearance. I have known customers who wouldn't adjust their valve clearances until hearing this ticking, as if the whole reason for adjusting the valves is to ensure a quiet engine; and conversely, others who believed no noise means all is well, no need to adjust anything. If the former is ignorant, the latter is dangerous. It is not for nothing that factory valve clearance adjustment intervals are spaced just 2,500 to 3,000 miles apart on 70s and older Hondas. It's a very important part of maintenance, right up there with ignition service.

More cam anatomy
Some people feel that measuring heel to nose and then measuring again ninety degrees to that and subtracting is a way to derive the cam's valve lift specification. As with many things, this sounds good but ignores reality. While having a purpose, the actual outcome of this Honda manual specified measurement is not to gauge the potential of your cam or compare it to another cam. You can't do those things by this measurement. It's too gross, it spans too many of the cam lobe's important regions all at once, areas of the cam that need to be separated to get meaningful specifications. The goal of the Honda manual's lobe height measurement is maintenance, not specification. It is simply an easy way to track cam wear, and you'll discover an astonishing rate of wear doing this. 1970s Honda fours' cams wear very quickly, as much as 0.001"-0.003" per thousand miles.

Three problems make the caliper measurement useless as a comparator. First, the cam's heel or base circle is not necessarily continuous for 180 degrees. Remember the ramps? So you're not really measuring the base circle with your micrometer at ninety degrees to the nose. Second, when the cam is from a rocker arm equipped engine, the cam's movement profile does not match the valve's; the valve sees a different movement scenario due to the rocker arm's ratio. Therefore valve movement, both duration and lift, on rocker arm engines is most accurately measured at the valve itself. Engine builders actually do it this way on all engines, whether rocker arms or shims and buckets type. It's that critical. Third, even on a given model engine, the cam's base circle diameter changes slightly from year to year (the CBX1000 is a perfect example), making the heel to nose measurement of absolutely no use in comparing cams. You can tell almost nothing significant from measuring the size of a cam lobe with a caliper or micrometer. Honda's reason for doing this is to track cam wear and nothing more.

Cam profiling
It's actually a lot more work than this to properly measure a cam. The most important, most useful, and most widely used cam detailing method is what is called "profiling" the cam. The cam is left in the engine, a degree wheel is affixed to the crankshaft, and a dial indicator is placed onto the valve. As the crankshaft is rotated, the indicator's readings are marked on a piece of graph paper every five degrees, and the result is a right-angle, X and Y, duration-versus-lift depiction of both the intake and exhaust valve movement caused by that cam. This is a tremendously useful tool for getting a meaningful "snapshot" of a cam, and thus for comparing camshafts. Not to mention its usefulness as part of building an engine whose parts come from different sources. Because it requires the same tools and setup, engine builders add yet another layer to the cam profiling process that measures the all-important valve-to-piston and valve-to-valve clearance at various crankshaft positions.

Cam degreeing
Degreeing a camshaft is simply using the same degree wheel and dial indicator to determine how much to slightly alter the valves' opening or closing times. On the intake especially, this is done to catch all of the inertia-laden airstream possible. But it's tricky. Too late a timing and the intake mixture's momentum dies and the gases actually back up in the port, sucking mixture out of the cylinder and causing a loss of power instead of a gain. Too early a timing and we've limited how full the cylinder can get. Either way, power is lost. The ideal thing is to close the intake valve at precisely the millisecond the mixture loses its momentum and stops. This is the whole point of making sure the cam, and in turn the intake valve, is in the correct position to make this happen. And this is far from "pie in the sky" esoteric, theoretical goings-on. I have put this in practice in everthing from 70cc to 1000cc Honda engines. It works.

Lobe center
Some people regard the lobe center calculation as a way to do the above. That is, to degree a cam. It certainly is used for that purpose by many. What the lobe center technique is really for however is comparing camshafts. Remember the cam lobe's acceleration and deceleration ramps and how tiny they are? They move the valve so slowly that judging exactly when the valve has opened or closed can be difficult. Because of this, engine builders ignore the ramps when profiling a cam. The ramp's purpose is to graduallly take up clearance--to "babysit" the valve. Builders disregard the valve's movement until the valve is past the ramp and has lifted a certain amount. At that "overshoot" distance they then start ticking the graph paper. This overshoot point is called the cam's "checking height." A checking height is merely a predetermined starting and stopping point in cam measurement that removes the cam lobe's ramps from the process.

Ecumenisizing
This makes profiling and degreeing more accurate. However, comparing cams is still a problem. Ramps aren't all the same size. The ramps on a pushrod engine's cam are the largest, because that engine's spindly valve train demands very gentle opening and closing curves. The ramps on overhead cam engines by contrast are much smaller, because there are fewer valve-related parts flailing about needing cushioning. Each engine design has its own size ramp and correspondingly its own recommended checking height; some 0.020", others 0.040", and still others 0.050". Comparison of these different cams therefore becomes meaningless, as two different checking heights give two very different valve timing measurements.

What's needed is a system of measuring valve timing which is independent of the checking height used. That is the lobe center technique. Though it still requires the use of a checking height, the lobe center approach indexes the cam based on an average of its opening and closing points--i.e., the cam's mathematical center. Different checking heights can be used on two identical cams and the lobe centers will still come out the same using the lobe center technique. Whatever the starting and stopping points are, the center is always the center, right? In this way, checking heights are removed from the measuring process and comparisons of one cam to another, even if they require different checking heights, is a simple process. Lobe center divorces checking height, once a hurdle in ecumenisizing cams, from cam measurement, making legitimate cam comparisons possible. That's why it was invented.

You might argue that no one compares the cam from a Harley Big Twin with that from a Hayabusa, and of course you're right. That isn't the kind of comparison we're talking about. Then why do we need the lobe center method to compare two differently-speced cams for the Hayabusa? Their checking heights will be the same, won't they? That's just it, they won't necessarily! Cam makers, each one having their own background and influences, continue to use different checking heights even on cams made for the exact same model motorcycle! Compare Honda's 0.040" checking height with Webcam's 0.050" and Dynoman's 0.020", for the exact same engine! Okay, then why isn't the cam's nose measured directly? Because it isn't the lobe's physical center we're looking for but its mathematical one.

As already mentioned, in recent years lobe center has been hijacked by some for use in timing cams to the engine instead of comparing cams. These folks propose that a particular lobe center works best on a particular engine design, i.e. larger lobe centers on Kawasakis and smaller ones on Hondas. An intriguing idea and it might well be useful. But not at all what the lobe center procedure was devised for, nor I contend is it the best way to time cams.