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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Additional or alternative engine breather
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<blockquote data-quote="peterg" data-source="post: 13271" data-attributes="member: 446"><p>Howdy Chaps,</p><p> </p><p>Would not stray to far into comparisons with cars unless reference is to a dry sump application. If you'll recall the ratio of displaced volume to total engaged volume - in this case it is very generous in wet sump applications. To draw the discussion back to the m/c side...can't recall whether it's here or JTAN but some of us have Indian Fours. These machines can be run with the 2 inch diameter oil fill cap on the side of the top case over the sump removed with only a bit of wispy blue smoke wafting out. Fire up a high ratio displaced/engaged volume twin like an HD or Indian with the timing plug removed from the case and you will have a spectacular display of noise (turbulence and high velocity) and a cloud of oil vapors issuing forth. Besides demonstrating the complete contrast in operating environment, that is an extreme illustration of what I'd pointed out earlier, namely any gases drawn back into the case must be dealt with on the next crank movement to BDC - the signature of open breathers. </p><p> </p><p>The point with a PCV - aptly name because it's primary function is knocking down positive crank case pressure to the level you desire - in this application is to draw down that pressure in successive crank revolutions after starting to a level achieved through the unit's internal ventsetting and/or your engaged volume's leagage (ie, breathing through the generator drive).</p><p> </p><p>The example of gas velocity at the vent pipe diminishing means the pressure differential has decreased which therefore lowers the velocity at that exit point and the propensity for atomized oil to escape. </p><p> </p><p>Some mention was made of scavenge pumps and cavitation if not assisted by positive crankcase pressure which may have merit. But, something to consider. Scavenge pumps on dry sump app's are generally much larger than their pressure counterparts because they are designed to evacuate aerated oil (more volume). Other applications where oil is subject to high aeration are turbochargers, but here, the sump tank allows the oil to stand momentarily before the scavenge pump draws it off for return to the main oil tank thus ensuring more oil over air content and therfore more efficiency. We don't have that here, windage and turbulence are conspiring to agitate the oil while the scavenge pump is attempting to work, therefore, if you can reduce those influences, what collects in the base of the case has more fluid content and the scavenge pump can therefore be more effective. I've not had my machines wet sump on a PCV but will readily admit to the longest riding session since fitment in January at 280 miles at 60 - 75mph, but, there's always that possibility, eh chaps?</p></blockquote><p></p>
[QUOTE="peterg, post: 13271, member: 446"] Howdy Chaps, Would not stray to far into comparisons with cars unless reference is to a dry sump application. If you'll recall the ratio of displaced volume to total engaged volume - in this case it is very generous in wet sump applications. To draw the discussion back to the m/c side...can't recall whether it's here or JTAN but some of us have Indian Fours. These machines can be run with the 2 inch diameter oil fill cap on the side of the top case over the sump removed with only a bit of wispy blue smoke wafting out. Fire up a high ratio displaced/engaged volume twin like an HD or Indian with the timing plug removed from the case and you will have a spectacular display of noise (turbulence and high velocity) and a cloud of oil vapors issuing forth. Besides demonstrating the complete contrast in operating environment, that is an extreme illustration of what I'd pointed out earlier, namely any gases drawn back into the case must be dealt with on the next crank movement to BDC - the signature of open breathers. The point with a PCV - aptly name because it's primary function is knocking down positive crank case pressure to the level you desire - in this application is to draw down that pressure in successive crank revolutions after starting to a level achieved through the unit's internal ventsetting and/or your engaged volume's leagage (ie, breathing through the generator drive). The example of gas velocity at the vent pipe diminishing means the pressure differential has decreased which therefore lowers the velocity at that exit point and the propensity for atomized oil to escape. Some mention was made of scavenge pumps and cavitation if not assisted by positive crankcase pressure which may have merit. But, something to consider. Scavenge pumps on dry sump app's are generally much larger than their pressure counterparts because they are designed to evacuate aerated oil (more volume). Other applications where oil is subject to high aeration are turbochargers, but here, the sump tank allows the oil to stand momentarily before the scavenge pump draws it off for return to the main oil tank thus ensuring more oil over air content and therfore more efficiency. We don't have that here, windage and turbulence are conspiring to agitate the oil while the scavenge pump is attempting to work, therefore, if you can reduce those influences, what collects in the base of the case has more fluid content and the scavenge pump can therefore be more effective. I've not had my machines wet sump on a PCV but will readily admit to the longest riding session since fitment in January at 280 miles at 60 - 75mph, but, there's always that possibility, eh chaps? [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Additional or alternative engine breather
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