The more recent the motorcycle, the less it vibrates, but back in the bad old days I would walk through the paddock seeing cracked exhaust pipes fairly often, and even a cracked frame or two. This is simple visual inspection—a good habit to have.

Parts under high stress, such as crankshafts and gears, may develop cracks that are initially invisible. The next step in sophistication is sensitive crack detection methods such as dye penetrant or Magnaflux. I would go to the welding supply and buy the cans—a spray solvent to clean surfaces, the dye penetrant itself, and a can delivering a film of fine chalky powder.

Clean the surfaces and dry them. Spray on the penetrant and let it sit according to directions. Wipe it away and again clean the surfaces. When at last you spray on the white powder, any dye that is hiding down in a crack in the part will wick into the absorbent powder and appear as a dye line. Eek, I have a crack.

Dye penetrant inspection works on any metal, but Magnaflux is useful only on ferromagnetic stuff.

Magnaflux is best explained by the grade school experiment in which you lay a sheet of paper on a small horseshoe magnet lying flat on a table. Now dust fine iron or steel particles onto the paper. The two poles of the magnet—North and south—are fairly close together. The magnetic flux established between the two poles causes the iron powder to line up with it, showing how the flux lines bulge out of the gap between poles.

A piece of steel with even a tiny crack in it, magnetized for this test, becomes a pair of N-S poles with field lines that arc up from the sides of the crack. Liquid containing the metal powder is applied and the particles try to line up with those field lines.

When we were racing two-stroke Yamaha TZ750s from 1974 to ’84, we at first had no gear problems. As time went on, little visual indications I saw led me to send the parts to a Magnaflux station. By that time we had found ways to make more power and in the last years we would have a crack indication after every national. Was this because we were making more power? Or were the gears made by an outside supplier whose QA was becoming a bit casual?

We also Magnafluxed a particular wheel in every crank, and found the beginnings of cracks we were already familiar with. This was confidence-inspiring, for I had seen such crank discs that had broken in other people’s bikes, wiping out the thousand dollar crankcase. The flywheel, spinning at 10,000 rpm, breaks in half, becoming a pair of “brake shoes” pressing outward, the friction instantly melting the inside surface of the crankcase. Time for the long lost Eleventh Commandment: “Thou shalt be rich.”

After we started Magnafluxing gears and crank parts, we never had a failure.

I began to wish secretly I could have myself Magnafluxed.