Armen
Serious Thumper
Online
Half-Witted Wrench-Jockey from Jersey
Posts: 1432
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Hey DBM, I started a thread about crank breathers a while ago, and got responses like I had two heads. Being very familiar with the BMW (boxer) race bikes and crew, I know how much grief they went through with crank breathing. Those bikes have the pistons up and down at the same time, so there is a pretty radical change in air volume in the bottom end. Also, having read more issues of Circle Track magazine than I should admit to, I know that any serious race car is using a vacuum pump in the bottom end to not only reduce crankcase air pressure, but actually run crankcase vacuum. The new Ducati holy sh-t twin has such an air pump. In the 70's, Todd Schuster made up a breather can out of a sheet metal paint can (rectangular size) that fit where the starter used to be. He filled it with Chore Boy or some sort of metal scrubby type stuff. The critical part, however, was the installation of a reed valve from a McCollough chain saw on the crankcase opening. The trick was to not let the air get pulled back in. Further refinements of the system were done. Udo Gietl (crew chief) came up with the idea of running a steel pipe into the exhaust system at an angle, toward the direction of exhaust flow. This pipe was then connected to the canister. The idea being that the pipe would create vacuum in the catch can. Which it did. Another variation was tried by Kenny Augustine (third genius of the Butler and Smith Wrecking Crew). Kenny ran a very small line from the oil catch can to the crankcase top. On piston upstroke, when some negative pressure would happen in the crankcase (remember, it was now a sealed system, with vacuum), the oil from the catch can would be sucked back into the crankcase. On my bike, I bought one of the OoohBabyOoohBabyOooh Ducati crank breather valves which has two reed valves and a tine return hole. Just this week I was doing a head scratch session trying to decide how/where to install the reed valve. So, start by putting some sort of one-way valve on the breather. If you can run it vertically, use a PCV valve from a car motor. If not, use a power brake booster canister one-way valve. I think you hit a limit when you were fighting crank pressure. I was actually going to try running a shop vac to the breather line if/when I finally dyno my motor.
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