When you start the engine, the excess oil in the crankcase is fired out the breather, onto the floor, (or into your air-filter on post-79 models). This is simply oil from the tank draining slowly back down into the crankcase while the bike is parked for any length of time. The most common causes of oil puking out the engine breather are listed below, in order of how common they are. Pretty simple but seems to cause repeated headaches for such a pesky little thing. I know there are other threads but cant find them right now. Some guys have found that plumbing in a 77-78 foo-foo valve on the later model engines improves breathing.ĭiscussion on foo-foo valves and engine breathers pics etc here: A Harley has two pistons and rods on one crankpin, so is one giant air compressor.
While a car engine is bigger, it has one piston coming down while one goes up, so not much change in internal crankcase volume, so not much breathing to be done. But they are not cheap.Īutomotive PCV valves are not really made to handle the revs or air volumes of a Harley. There is a product called a Krankvent that can be plumbed into the lower, 6 o’clock position as an alternative to a stock foo-foo valve. You can see the 9 oclock fitting and the 6 oclock fitting both enter the same cavity. Just to add to the knowledge base, here is a pic of IronMick's internal foo-foo in his post-79 model. That is fine too, as long as you are not an EPA man. Many of these bikes with custom air filters simply run that hose down to the bottom of the frame and let the oil mist blow out in the time honored manner. It connected to the stock air filter so that any oil mist was fed back through the engine, making the EPA pollutocrats more happier than they were with the idea of engine oil spraying out into the atmosphere.
84 harley evo camshaft cover bottom breather tube generator#
A rubber breather hose then ran from the generator drive area of the timing cover, at the 9 o’clock position. Instead, a one-way foo-foo valve was built in inside the timing cover. The external foo-foo valve and the six-inch metal vent tube at the front of the timing cover were done away with. Searching this site for foo foo or foo-foo will lead to extensive discussion of this mystical device. It is sometimes referred to as the foo-foo valve. An external non-return valve was plumbed into that vent tube sticking down from the timing cover at the generator drive. The timed breather on the oil pump drive was dropped. A metal disc on the end of the generator drive gear centrifugally separates oil from the air as it is discharged overboard.
A six-inch metal tube hanging down from the timing cover near the generator drive, at the 6 o’clock position vents that controlled pressure to atmosphere. There is a timed breather valve built into the oil pump drive, which vents crankcase pressure into the cam timing chest. It is commonly done, but it wastes power and is not good for your engine. One thing not to do with an engine breather is to simply plumb a hose to the crankcase without some kind of one-way valve or timed breather valve. Old time tuners like Jerry Branch, Tom Sifton and Dick O’Brien paid much attention to the engine breather because they knew it could give them extra horsepower if set up right. Without some kind of controlled breather, the lower end would become a 1,000cc air compressor, robbing the engine of several horsepower. The engine breather, or crankcase vent as Harley sometimes calls it, is to allow air out of the lower crankcase, but not in, as the pistons rise and fall. This seems to be a recurring question, and we have various threads addressing it, so here is a summary and links.
0 kommentar(er)
