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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Additional or alternative engine breather
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<blockquote data-quote="John Appleton" data-source="post: 13196" data-attributes="member: 760"><p><span style="font-family: 'Arial'"><span style="font-size: 10px"><span style="font-family: 'Times New Roman'"><span style="font-size: 12px">I think it would be of great benefit to the many owners who have tinkered/modified the standard breather to hear of any possible downside in doing so, and less returning oil sounds rather ominous!</span></span></span></span></p><p>I would certainly like to hear more-- please.</p><p>Regards,Col.</p></blockquote><p></p><p>I am sure trevor is trying to get you all to put your thinking caps on before modifying anything with more enthusiasm than skill. Let us consider the conditions in the crankcases, and there are three possible variations on the pressures involved. </p><p>The first is pressure too high. Possible causes are blowpast at the piston rings or mistimed breather.</p><p>The second is pressure too low ie a partial vacuum. Possible cause mistimed breather.</p><p>The third is neutral ( ie atmospheric)</p><p>If the pressure is too high it will lead to oil leaks at the weaker sealing faces, but the scavenge pump will have an easy time as the pressure will help it in its designed task.</p><p>If the pressure is too low (partial vacuum) there will be no oil leaks, but the scavenge pump will have to overcome this depression before it can return any oil to the tank. In an extreme case it is conceivable that it will not work at all !</p><p>If the pressure is neutral (ie atmospheric) it would suggest that the breather is sucking and blowing leading to large quantities of dirt entering the crankcasing unless an efficient filtration system is employed.</p><p>There are many other pros and cons for each condition described, but these will give you the idea.</p><p>I have looked at various solutions that people have come up with and can see shortcomings in some of them . The most obvious of these concerns the breathers which are vented through either the valve spring or push rod caps. The valve gear depends on some of its oil running back down the pushrod tubes, and the last thing it needs are great gouts of displaced air pushing it back to where it came from. this displaced air is also being forced to pick up some of this oil and carry it with it out through the breather pipe.</p><p>The elephant trunk breather seems to me to be one of the better ideas, but to my eye is ugly.</p><p>I am using a home brewed system which consists of a chamber , fitted in place of the ATD cover, which is separated from the timing chest by a poppet valve held closed by a very light spring. The fumes which pass this valve are automatically deflected onto the walls of the chamber which has the effect of separating the oil content. In the bottom of the chamber is a 3mm hole through which the oil is sucked back into the engine as the pistons rise. The fumes pass out of the chamber through a 1/2inch o/d tube, the inlet of which is at the highest point of the chamber and this tube exits the chamber at the bottom and down under the engine through a convenient hole in the front propstand plate.</p><p>I have retained the original breather and , by virtue of the poppet valve, the extra breather can be considered as an auxhillary which only operates when the pressure rises to an unacceptable level.</p><p>It works.</p><p>John</p><p>[/QUOTE]</p>
[QUOTE="John Appleton, post: 13196, member: 760"] [FONT=Arial][SIZE=2][FONT=Times New Roman][SIZE=3]I think it would be of great benefit to the many owners who have tinkered/modified the standard breather to hear of any possible downside in doing so, and less returning oil sounds rather ominous![/SIZE][/FONT][/SIZE][/FONT] I would certainly like to hear more-- please. Regards,Col.[/QUOTE] I am sure trevor is trying to get you all to put your thinking caps on before modifying anything with more enthusiasm than skill. Let us consider the conditions in the crankcases, and there are three possible variations on the pressures involved. The first is pressure too high. Possible causes are blowpast at the piston rings or mistimed breather. The second is pressure too low ie a partial vacuum. Possible cause mistimed breather. The third is neutral ( ie atmospheric) If the pressure is too high it will lead to oil leaks at the weaker sealing faces, but the scavenge pump will have an easy time as the pressure will help it in its designed task. If the pressure is too low (partial vacuum) there will be no oil leaks, but the scavenge pump will have to overcome this depression before it can return any oil to the tank. In an extreme case it is conceivable that it will not work at all ! If the pressure is neutral (ie atmospheric) it would suggest that the breather is sucking and blowing leading to large quantities of dirt entering the crankcasing unless an efficient filtration system is employed. There are many other pros and cons for each condition described, but these will give you the idea. I have looked at various solutions that people have come up with and can see shortcomings in some of them . The most obvious of these concerns the breathers which are vented through either the valve spring or push rod caps. The valve gear depends on some of its oil running back down the pushrod tubes, and the last thing it needs are great gouts of displaced air pushing it back to where it came from. this displaced air is also being forced to pick up some of this oil and carry it with it out through the breather pipe. The elephant trunk breather seems to me to be one of the better ideas, but to my eye is ugly. I am using a home brewed system which consists of a chamber , fitted in place of the ATD cover, which is separated from the timing chest by a poppet valve held closed by a very light spring. The fumes which pass this valve are automatically deflected onto the walls of the chamber which has the effect of separating the oil content. In the bottom of the chamber is a 3mm hole through which the oil is sucked back into the engine as the pistons rise. The fumes pass out of the chamber through a 1/2inch o/d tube, the inlet of which is at the highest point of the chamber and this tube exits the chamber at the bottom and down under the engine through a convenient hole in the front propstand plate. I have retained the original breather and , by virtue of the poppet valve, the extra breather can be considered as an auxhillary which only operates when the pressure rises to an unacceptable level. It works. John [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Additional or alternative engine breather
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