4-STROKE VALVE LAPPING 101

It has been almost 50 years since O.S. introduced its first 4 -stroke engine, the O.S. FS-60. Although it was credited with marketing the world’s first glow-ignition 4-stroke, a .45 displacement engine called the “Kalt” preceded O.S. by a few months. The Kalt, however, was only produced in limited quantities, whereas the O.S. was the first to be mass-produced. At the time, many of us wondered what possible use we could have for a 4-stroke....