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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
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<blockquote data-quote="highbury731" data-source="post: 104635" data-attributes="member: 1557"><p>The best example I know, of crank case pressure control being important for oil control and power is a sohc Norton single. They rely on rubber pads pressing on the top and bottom surface of the rockers to restrict oil flow out of the cam box. The crank shaft has a small diameter hole through the mainshaft which acts as a timed crank case breather. The motors pump oil out, especially from the cam box. Fastidious owners set the rubber 'seals' for heavy pressure to try and keep the oil inside the engine - and that costs power.</p><p>A more beneficial approach is to fit a flap valve to a much larger crank case vent, so that it runs under proper negative pressure. A smaller secondary flap valve between crank case and lower bevel chamber will enable the lower bevel chamber to run under negative pressure. That helps the oil drain from the cam box (they suffer from over-filling), and greatly reduces the flood of oil all over the engine and the rider's legs. And gives a signifcant power boost, especially if the owner has been using high pressure on those silly rubber cam box pads.....</p><p>Paul</p></blockquote><p></p>
[QUOTE="highbury731, post: 104635, member: 1557"] The best example I know, of crank case pressure control being important for oil control and power is a sohc Norton single. They rely on rubber pads pressing on the top and bottom surface of the rockers to restrict oil flow out of the cam box. The crank shaft has a small diameter hole through the mainshaft which acts as a timed crank case breather. The motors pump oil out, especially from the cam box. Fastidious owners set the rubber 'seals' for heavy pressure to try and keep the oil inside the engine - and that costs power. A more beneficial approach is to fit a flap valve to a much larger crank case vent, so that it runs under proper negative pressure. A smaller secondary flap valve between crank case and lower bevel chamber will enable the lower bevel chamber to run under negative pressure. That helps the oil drain from the cam box (they suffer from over-filling), and greatly reduces the flood of oil all over the engine and the rider's legs. And gives a signifcant power boost, especially if the owner has been using high pressure on those silly rubber cam box pads..... Paul [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Not another breather thread!
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