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PCV
My bike (1981 XS1100 SH) doesn't have a PCV valve, but the vent tube from the crankcase goes into the air box with tubes curved around into the carb inlets. This would give a sort of positive ventilation, through a venturi effect.
PCV valves are designed to be hooked up to a strong vacuum source, and pull air through the crankcase. On vehicles, especially the older ones with a round pan type air cleaner, you will see a separate filter, or a tube that opens inside the filter and goes to a valve cover. This is the fresh air intake for the PCV system. When this gets plugged, the crankcase gets vacuum applied to it and seals start going south. The sole purpose of the PCV valve is to prevent an intake backfire from igniting crankcase gasses and blowing the engine apart. I have seen old chevy engines with the valve covers swelled up like a balloon, because someone did away with the PCV valve.
In order for any bike like mine to effectively use a PCV system, there would need to be a fresh air intake going into some place far away from the breather. Most likely, it would be easier to mill or drill an appropriately sized hole into the valve cover, and put a grommet and pcv valve from a car engine in there supplied with vacuum. Then remove the curled tubes from the air box, while letting the crankcase breather be the fresh air intake. One would have to find a place there is not much oil flying around for the pcv valve, or make a baffle for it, lest the engine ingest large amounts of oil into the combustion chamber, and the rider be accused of fogging mosquitoes out of season.
the benefit of a PCV system over a breather is the continuous removal of combustion gasses from the crankcase. Those gasses are highly acidic. Think 78% nitrogen atmosphere combined with Hydrocarbon byproducts, and you have nitrous and nitric acid elements, along with the normal water vapor inherent in any hydrogen oxygen combustion, and the engine oil goes to pot rather quickly. A breather only equalizes pressure, and does not evacuate combustion gasses.
FINALLY! That stupid ASE test has been useful. It never got me a better job or got me a raise, but at least I get to look like an intelligent person on the net (or a smart a**, which ever fits)
My bike (1981 XS1100 SH) doesn't have a PCV valve, but the vent tube from the crankcase goes into the air box with tubes curved around into the carb inlets. This would give a sort of positive ventilation, through a venturi effect.
PCV valves are designed to be hooked up to a strong vacuum source, and pull air through the crankcase. On vehicles, especially the older ones with a round pan type air cleaner, you will see a separate filter, or a tube that opens inside the filter and goes to a valve cover. This is the fresh air intake for the PCV system. When this gets plugged, the crankcase gets vacuum applied to it and seals start going south. The sole purpose of the PCV valve is to prevent an intake backfire from igniting crankcase gasses and blowing the engine apart. I have seen old chevy engines with the valve covers swelled up like a balloon, because someone did away with the PCV valve.
In order for any bike like mine to effectively use a PCV system, there would need to be a fresh air intake going into some place far away from the breather. Most likely, it would be easier to mill or drill an appropriately sized hole into the valve cover, and put a grommet and pcv valve from a car engine in there supplied with vacuum. Then remove the curled tubes from the air box, while letting the crankcase breather be the fresh air intake. One would have to find a place there is not much oil flying around for the pcv valve, or make a baffle for it, lest the engine ingest large amounts of oil into the combustion chamber, and the rider be accused of fogging mosquitoes out of season.
the benefit of a PCV system over a breather is the continuous removal of combustion gasses from the crankcase. Those gasses are highly acidic. Think 78% nitrogen atmosphere combined with Hydrocarbon byproducts, and you have nitrous and nitric acid elements, along with the normal water vapor inherent in any hydrogen oxygen combustion, and the engine oil goes to pot rather quickly. A breather only equalizes pressure, and does not evacuate combustion gasses.
FINALLY! That stupid ASE test has been useful. It never got me a better job or got me a raise, but at least I get to look like an intelligent person on the net (or a smart a**, which ever fits)
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