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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: 13135" data-attributes="member: 446"><p><strong>Breather: PCV</strong></p><p></p><p><span style="color: #323232"><span style="font-family: 'Verdana'">Howdy Sir,</span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">One from the “similar modification” camp on exhaust rocker mounted PCV’s, you can view my simple solution <a href="http://www.vincentownersclub.co.uk/forum/album.php?albumid=9&pictureid=64" target="_blank">here</a> in our photo section.</span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">For old hands here the Vin breather subject has been flogged for 60 years but some new members to the fold may benefit from further bleatings on the topic so bear with me for (way more than) a moment. Like shock absorbers and ATD’s, timed breathers were in their relative infancy in the mainstream as m/c manufacturers transitioned away from crankcase turbulence as a supplement to early (inadequate) positive pressure lubrication systems. The mere presence of an un-valved atmospheric breather like the “D” indicates that the makers here were more inclined to evacuate positive pressure than use it to drive atomized oil to the far reaches of the engaged volume to supplement the oil pump. So therein lies our mission. Reduce positive pressure…but for many of us without complete sealing (ie, valve stems and generator drive) not stray too far into a significant vacuum as other issues can arise. </span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">So, some primary elements for consideration are displaced volume (at BDC) and vent velocity, the latter to be viewed as a reverse of the preferred environment to atomize fuel. You want to reduce the displaced volume over time, thereby enabling use of a smaller breather device which is porting less gases at lower velocity so the oil has a chance to drop out before being vented. By installing a PCV, you will note on engine start up a high volume of gases vented at rather high velocity but in a matter of seconds it will begin to draw down positive crankcase pressure thereby reducing volume and velocity. If mounted vertically atop your #2 exhaust rocker cap you will benefit from the pushrod tube, cap and PCV acting as a vertical standpipe to let surface tension capture the now more slowly passing mist, converting into droplets which thereafter can drain back into the sump. </span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">The issue with the timed breather? It is just that, timed, it cannot control vacuum and pressure to the degree a PCV can, which being pulse activated is constantly on duty and can be tuned by virtue of activating</span></span><span style="color: #323232"><span style="font-family: 'Verdana'"> spring pressure and controlled vacuum leakage. Worse, its position low nearer the source of the pressure differential – the port in the timing side case leading to the crankcase gallery – where that port, acting as venturi is atomizing oil centrifuging off your flywheels and now blown out into the timing chest at BDC. Whereas the breather sleeve may be large enough to handle some volume it is completely negated by the restrictive banjo fitting and no benefits of surface tension to capture oil mist in these high velocity gases can be realized because the line is routed immediately downward to exit. </span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">The rap on open atmospheric breathers is that any atmosphere being ingested as the pistons rise to TDC must be re-expelled on descent to BDC so these devices have to work at the high end of displaced volume all the time to be effective and that is why bigger (and more obtrusive) is better. Admittedly by its size, an Elephant trunk is very effective at de-atomizing vented gases of oil by virtue of lowering velocity, presenting lots of capture area for surface tension to work and nearly a foot vertically to conduct this process on. </span></span></p><p> </p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'">Admittedly, my two machines fitted with the above PCV and timed breather blanked off do leave a few drops after a ride because I have elected not to fit any capture device, like say a wire mesh pad inside vessel along the lines of the old vent caps on old car valve covers, but the total elimination of oil wafting out the de-compressor hole in the timing cover to liven up handling from an oily rear tire is more than payback. </span></span></p><p> </p><p><span style="color: #323232"><span style="font-family: 'Verdana'"><img src="http://www.vincentownersclub.co.uk/forum/picture.php?albumid=9&pictureid=63" alt="" class="fr-fic fr-dii fr-draggable " style="" /></span></span></p></blockquote><p></p>
[QUOTE="peterg, post: 13135, member: 446"] [b]Breather: PCV[/b] [COLOR=#323232][FONT=Verdana]Howdy Sir,[/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]One from the “similar modification” camp on exhaust rocker mounted PCV’s, you can view my simple solution [URL="http://www.vincentownersclub.co.uk/forum/album.php?albumid=9&pictureid=64"]here[/URL] in our photo section.[/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]For old hands here the Vin breather subject has been flogged for 60 years but some new members to the fold may benefit from further bleatings on the topic so bear with me for (way more than) a moment. Like shock absorbers and ATD’s, timed breathers were in their relative infancy in the mainstream as m/c manufacturers transitioned away from crankcase turbulence as a supplement to early (inadequate) positive pressure lubrication systems. The mere presence of an un-valved atmospheric breather like the “D” indicates that the makers here were more inclined to evacuate positive pressure than use it to drive atomized oil to the far reaches of the engaged volume to supplement the oil pump. So therein lies our mission. Reduce positive pressure…but for many of us without complete sealing (ie, valve stems and generator drive) not stray too far into a significant vacuum as other issues can arise. [/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]So, some primary elements for consideration are displaced volume (at BDC) and vent velocity, the latter to be viewed as a reverse of the preferred environment to atomize fuel. You want to reduce the displaced volume over time, thereby enabling use of a smaller breather device which is porting less gases at lower velocity so the oil has a chance to drop out before being vented. By installing a PCV, you will note on engine start up a high volume of gases vented at rather high velocity but in a matter of seconds it will begin to draw down positive crankcase pressure thereby reducing volume and velocity. If mounted vertically atop your #2 exhaust rocker cap you will benefit from the pushrod tube, cap and PCV acting as a vertical standpipe to let surface tension capture the now more slowly passing mist, converting into droplets which thereafter can drain back into the sump. [/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]The issue with the timed breather? It is just that, timed, it cannot control vacuum and pressure to the degree a PCV can, which being pulse activated is constantly on duty and can be tuned by virtue of activating[/FONT][/COLOR][COLOR=#323232][FONT=Verdana] spring pressure and controlled vacuum leakage. Worse, its position low nearer the source of the pressure differential – the port in the timing side case leading to the crankcase gallery – where that port, acting as venturi is atomizing oil centrifuging off your flywheels and now blown out into the timing chest at BDC. Whereas the breather sleeve may be large enough to handle some volume it is completely negated by the restrictive banjo fitting and no benefits of surface tension to capture oil mist in these high velocity gases can be realized because the line is routed immediately downward to exit. [/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]The rap on open atmospheric breathers is that any atmosphere being ingested as the pistons rise to TDC must be re-expelled on descent to BDC so these devices have to work at the high end of displaced volume all the time to be effective and that is why bigger (and more obtrusive) is better. Admittedly by its size, an Elephant trunk is very effective at de-atomizing vented gases of oil by virtue of lowering velocity, presenting lots of capture area for surface tension to work and nearly a foot vertically to conduct this process on. [/FONT][/COLOR] [COLOR=#323232][FONT=Verdana]Admittedly, my two machines fitted with the above PCV and timed breather blanked off do leave a few drops after a ride because I have elected not to fit any capture device, like say a wire mesh pad inside vessel along the lines of the old vent caps on old car valve covers, but the total elimination of oil wafting out the de-compressor hole in the timing cover to liven up handling from an oily rear tire is more than payback. [/FONT][/COLOR] [COLOR=#323232][FONT=Verdana][IMG]http://www.vincentownersclub.co.uk/forum/picture.php?albumid=9&pictureid=63[/IMG][/FONT][/COLOR] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Additional or alternative engine breather
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