Big things were happening as the 19th century neared its end. Wars in Europe (Austro-Prussian, Franco-Prussian) and in the US (American Civil War) had required vast amounts of materiel that could only be produced by new industrial methods. The emergence of professional and managerial middle classes with serious spending power swelled national economies. This was a time of open-ended innovation in machinery and transportation, presenting fantastic opportunities for engineers and inventors. We know the far-reaching effects of railroads, steamships, electric power, and machine tools, but more subtle and less known is the influence of so-called "anti-friction" bearings, which easily carry heavy loads on balls or rollers.

Here’s a success story for you. In 1883, Friedrich Fischer in Schweinfurt, Germany, devised a grinding machine to produce high-hardness steel balls. Such balls, rolling in U-shaped grooves ground into ring-like inner and outer races, assembled into the first industrial ball bearings. By 1890, Fischer could make balls accurate to 0.001 inch. Two years later, accuracy doubled to 0.0005 inch.

The Marmon automobile in which Ray Harroun so calculatingly won the first Indianapolis 500 mile race on May 30, 1911, rolled on FAG ball bearings.

This was the bearing that made the bicycle—and later, the motorcycle—possible because its very low friction so greatly reduced the effort required for transportation. By 1896, Fischer was producing 10 million accurately spherical steel balls per week. The bicycle boom that swept the industrial nations from 1896 onward was only a part of this rolling explosion.

Fischers Aktien Gesellschaft became the FAG Corporation, which remains in the rolling-bearing business to this day. The Marmon automobile in which Ray Harroun so calculatingly won the first Indianapolis 500 mile race on May 30, 1911, rolled on FAG ball bearings.

Crankshaft classic
"If you're really in a hurry," Cycle World wrote about Kawasaki's 500cc H1 in the June 1973 issue, "7,500 rpm and the resulting 60 hp will get you upward of the ton in no time at all." Many years later, an advertisement for a used H1 crankshaft reads, "Main bearings feel good with no excessive play or tightness." Yours for $250…Cycle World archives

An assembled ball bearing consists of inner and outer races, each with facing U-section circular grooves (the “races”) in which a complement of steel balls roll. The balls are separated from each other by one of several possible forms of ball separator. To assemble such a bearing, place the two races flat on a surface, one within the other, push the inner race to one side, and pour the balls into the crescent-shaped space this produces. Now snap the inner race to its central position and with a pencil point, space the balls equally around the bearing. Now the ball separator (also called a “cage”) can be installed over the balls. The separator is necessary both to space the balls equally and to prevent ball-to-ball rubbing.

The now-common snap-in molded plastic cage pops into place from one side, but the traditional two-piece steel ribbon separator installs as one half from each side. The two halves of the separator are then riveted, spot-welded, or fastened to each other with bending tabs, forming a ring of circular pockets in which the balls spin.

The radius of the raceways is always greater than the radius of the balls, so contact from ball to raceway is initially a single point, broadening under load to a small ellipse.

Complete stoppage hadn’t occurred yet but would as soon as a loose piece of cage got caught under a ball, making it skid, heat rapidly, and weld the bearing into a dark-blue lump.

This cannot be a tight assembly; some ball-to-raceway clearance is necessary to make room for oil films and provide clearance for heat expansion of the balls at operating temperature. When a ball bearing’s inner race is pressed onto a shaft, it is expanded slightly and the outer race may be compressed a bit if pressed into a housing or clamped between crankcase halves. Because this may cause bearing internal clearance to disappear, replaced by preload, bearing failure can occur prematurely. To prevent this, bearings with increased internal clearance are made, identified as “C3” by marking on the faces of the outer race. Bearing size (such as 6005, 6305, etc.) is also marked on the outer race. Consult bearing catalogs for dimensions, installation advice, and other interesting information.

I learned a few things about the dynamics of ball bearings from rebuilding crankshafts. A man arrived at the shop one day with his year-old white 1969 Kawasaki H1, which was making ominous crispy scraping noises as it idled. When I had the crank out of the engine and disassembled it using the hydraulic press, I could see the problem clearly. The bearing balls and races were fine; their surfaces were still smooth. The noise was coming from a ball separator that had cracked and was coming apart. Complete stoppage hadn’t occurred yet but would as soon as a loose piece of cage got caught under a ball, making it skid, heat rapidly, and weld the bearing into a dark-blue lump.

I asked a rolling-bearing engineer how cages crack. He replied that in bearings operating at high speed, the balls don’t roll smoothly around their races in ideal fashion but instead can oscillate rapidly from side to side, stressing the separator. A steel ribbon separator has regions of high stress around its rivets and where it has been press-formed to make the ball pockets. Those are the likeliest places for cracks to start. Now I always look carefully at both faces of any used bearing, looking for cracks in the separator.

That 1970 customer had 50,000 miles on his bike, as he told us, “Mostly at 100 mph up and down the Maine Turnpike.” That’s 200 million rotations of the crankshaft. Wouldn’t you feel fatigued after 200 million reps? At the time, dealer net on crankshaft main bearings was around a dollar apiece (six bearings on those three-cylinder cranks), which I figured was good value for money. I put a freshly rebuilt crankshaft into that customer’s engine, and once the engine was back in place, he rolled away.

The failures I’ve seen in roller bearings usually occur on the surface of the inner race as regions in which the surface case hardening has been crushed; hence the name, “case crushing.” Subsurface metal fatigue from the stress of the rollers rumbling over it millions of times brings tiny cracks into being, some of which propagate. Those that reach the surface begin to release fragments.

More commonly, rolling bearings in motorcycles fail by rusting while the bike is stored outdoors or in damp basements. That crank was perfect as it started to snow in November, but when the owner shoveled the bike out in early spring and brought it to us, he wrote on the repair order, “Kickstart lever does not go down. Get running.” Classic!