Harley motorbike why blow back thru new motor 4000 k,old
Regrettfully, all Harley engines suffer from this problem to a greater or lesser degree. It is due to the use of the single crankpin design of the engine. This design is what gives the Harley-Davidson it's distinctive sound but it does create a tremendous amount of crankcase pressure. This is due to the two very large piston moving up and down in unison with each other.
The late model engines went to what we call a "head breather" design in that crankcase pressure is relieved at the top of the engine rather than the earlier design that relieved the pressure at the lower side of the engine. This is accomplished by the use of "umbrella valves" in the center piece of the rocker box covers. The "umbrella valves" are made of synthetic rubber and open and close the breather passages from the rocker box to the air filter box by flexing in responce to the crankcase pressure. Due to repeated heating and cooling, the umbrella valve gets a bit stiff and fails to seal completely allowing oil to be blown into the air filter. Sportsters are more subject to the problem than the Big Twins for some reason.
Most people purchase one of the aftermarket crankcase breather systems and install this or they simply reroute the crankcase breather to the underside of the engine using longer hoses and plug the holes in the backside of the air filter assembly.
However, if the laws in your area preclude you of making any modifications such as this, I would purchase a K&N washable filter and install it in the air filter assembly. These filter are washable and can be cleaned and reused over and over again. As I said, this oil getting into the air filter is aggrevating but also normal unless it gets to where it's pouring out everytime you ride it after cleaning. At point, you need to replace the gaskets and umbrella valve in the rocker boxes. Good Luck
Dec 20, 2009 |
2000 Harley Davidson XL 1200 S Sportster...