First was heavy vibration, caused by the engine’s one-up/one-down 180-degree firing order, which broke front exhaust pipes (until the team provided a spring-joint in that pipe at the failure point) and sometimes
shook the check-valve in the front brake master cylinder such that the rider could pull the lever to the bar without effect. At the US Loudon national the vibration of Harry Klinzmann’s KR-250 broke four of the six tubes supporting its steering head, allowing the remaining two to bend as the front wheel raked itself out!
The vibration problem was solved by changing firing order to 360 degrees (both pistons moving up and down and firing together). When used with a 100-percent balance factor this made the engine quite smooth because:
At TDC and BDC the pistons were going one way and the balance weights the opposite.
At mid-stroke, the front balance weight was yanking forward and the rear crank's weight was yanking backward.
The contra-rotating cranks were geared together by two thin, roughly 4-inch diameter phasing gears, which dipped into gearbox oil. Spinning at 12,000-rpm these gears whipped such heat into the gear oil that paint was burned off the early engines. The first-order “fix” was to drop the original 1,100cc gearbox oil quantity (up to the shaft axes) to 600cc (mostly only first and second wheels actually now touched the oil)
A better fix was to separate the phasing gears from the gearbox oil with a “fence” save for a 1mm hole to let oil in. Gear action would then throw the used oil back “over the fence.” The low oil level required pre-lubing every gear during assembly, for otherwise a dry gearbox would squeal at first start-up.
Originally Posted by wobbly
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