~ Auto Buzz ~: ESSAY: Engine Blow-Ups Suddenly, my bike developed a two-piece crank.

When I first started going to races, people were fond of the dramatic. Your bike didn’t just stop running, it “blew up.” Blow-ups were common. Unlike the present, production bikes were nowhere near being “raceable.” To get something close to reliability, your bike had to be built by someone with real knowledge. And even that was no guarantee. So off to the races people went. When a BSA Gold Star single came apart, the part of the rod still attached to all the energy stored in its spinning flywheels quickly poked holes in the crankcase. Another legendary “blower-upper” was the Triumph Cub, sometimes referred to as “the bearing-thrasher.” Just as Honda does to this day when one of its MotoGP engines “stops running” (that is, ejects valves and other important organs onto the track), Harley-Davidson used to announce the cause of the mechano-mayhem as “magneto failure,” or simply “electrical.” When Yvon DuHamel’s Kawasaki H2R engine nearly sawed itself in half on the Talladega banking, the “active” end of the broken rod poked through into the gearbox, releasing its quart-and-something of hot oil onto the pipes below, igniting a 30-foot-long comet’s tail of fire. Chaos management? Yvon was equal to the task. Those Kawasakis done blowed-up much better than a Gold Star because in addition to the energy in the H2R’s six flywheels, the other two cylinders kept right on firing, enabling the broken rod stub to keep right on sawing. Sometimes that year [1973] a rider would bring the bike back to the pits, still running, saying, “It doesn’t sound right.” You bet.

The great thing about those blow-ups was this: The missing parts—wristpin, wristpin bearing cage, needles, and gritty pieces of piston—generally ended up in the exhaust pipe. Best to remove and upend the pipe of any cylinder that has come to grief. It’s just like replacing the oil cooler after a bottom-end failure…there’s no telling what debris may be lurking there, waiting to do bad things to the replacement engine. Endurance-racing Suzuki GSX-R11000s of the oil-cooled era could break their cranks, especially if tuned to pull from lower revs. This suggested that one of the flywheel pairs was doing the “elephant-ears” vibration mode. It wasn’t a material problem, because making special cranks out of “Spaceman Spiff” alloy gave the same result. Another from the same era was the offset-pin crank from the Super Hawk Honda V-twin. People loved those bikes, which ran well with stock redline. But start revving them to 10,000 or so and one day, “Mmm, my motor feels funny.” It had developed a two-piece crank. There was a period in the 1990s when Ducati Superbikes seemed to need an engine change for every practice because the crankcases and cylinder spigots were overworked. Redesign and eventual adoption of one of the new casting processes [Ritter Vacural] fixed that action. As power grows, so must component strength. See all the deep under-engine sumps on race bikes? They come from hard experience. If the oil pump gets air, it’s delivered to the bearings under pressure, so it can sneeze the oil out. In an instant, journal and bearing shells become one in the process known as “spinning a bearing.” Reliable operation can only result from good design, adequate testing, tight control of parts quality, and enlightened assembly. Just do everything perfectly and you might be in with a chance.