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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Elephant trunk breather
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<blockquote data-quote="Nigel Spaxman" data-source="post: 98776" data-attributes="member: 2907"><p>The problem with the timed breather is it seems like the factory, Phil Irving, Richardson and pretty well everyone got it wrong!! The breather doesn't need to open anywhere near TDC. BDC is the wrong place to close it. The idea seems to be that the crankcase is like a liquid pump and the outlet needs to be open as the volume is reducing. It is not a liquid pump. The crankcase has a compressible gas in it, but it is not filled with gas, unless the blow by is really severe. It needs to be open when the volume of the crankcase is smallest. If it opens anywhere during the top part of the stroke air is likely to go in through the breather, then it has to try to go out again near BDC, but then with the normal timing it closes. </p><p></p><p>The breather needs to open no sooner that 90 degrees after TDC and close about 90 degrees after BDC or it can be open a bit less. The main thing is it needs only to be open when the pressure is higher than atmospheric. You have to try to get it to do what a very quick acting check valve like a reed valve can do. It needs to be open only when the pressure is above atmospheric. It can do this really well if it is timed right, it doesn't even have to be that exact to work. The trouble is a lot of the information in the Vincent world encorages people to time them in a way that is not optimal.</p></blockquote><p></p>
[QUOTE="Nigel Spaxman, post: 98776, member: 2907"] The problem with the timed breather is it seems like the factory, Phil Irving, Richardson and pretty well everyone got it wrong!! The breather doesn't need to open anywhere near TDC. BDC is the wrong place to close it. The idea seems to be that the crankcase is like a liquid pump and the outlet needs to be open as the volume is reducing. It is not a liquid pump. The crankcase has a compressible gas in it, but it is not filled with gas, unless the blow by is really severe. It needs to be open when the volume of the crankcase is smallest. If it opens anywhere during the top part of the stroke air is likely to go in through the breather, then it has to try to go out again near BDC, but then with the normal timing it closes. The breather needs to open no sooner that 90 degrees after TDC and close about 90 degrees after BDC or it can be open a bit less. The main thing is it needs only to be open when the pressure is higher than atmospheric. You have to try to get it to do what a very quick acting check valve like a reed valve can do. It needs to be open only when the pressure is above atmospheric. It can do this really well if it is timed right, it doesn't even have to be that exact to work. The trouble is a lot of the information in the Vincent world encorages people to time them in a way that is not optimal. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Elephant trunk breather
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