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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
more on breathers
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<blockquote data-quote="paulpackman" data-source="post: 51038" data-attributes="member: 1804"><p>I cracked this one years ago.</p><p>The crankcase volume changes by nearly one litre at every rev as both pistons go up and down almost together and so breathing is a problem</p><p>especially when you add to it blow by past the pistons. Any atmospheric breather must be of low inertia (no ball valves) so that it is sensitive</p><p>to the pulses of the engine up to 6000 rpm or so. </p><p>Firstly your bike should have good bores and rings otherwise you will be wasting your time. </p><p>I have blanked off the timed breather and fitted a Kevlar disc valve (low inertia) on the top cap of the front exhaust valve of my twin </p><p>which is very obscure, out of the way and does not spoil the look of the bike.</p><p>I drilled holes in the underside (non stressed part) of the exhaust rocker housing and ported past the upper valve guide giving a</p><p>vent of about half an inch square. The valve housing is the full diameter of the top cap and has eight quarter inch holes in it over</p><p>which a Kevlar disc is attached. I have blanked off the oil feed to the front rocker as enough oil mist gets up there from the engine</p><p>which drops out in the large diameter valve cap from which a half inch pipe leads to the back of the bike.</p><p>All I get from the end of the breather pipe is a little moisture from the products of combustion. </p><p> QED</p></blockquote><p></p>
[QUOTE="paulpackman, post: 51038, member: 1804"] I cracked this one years ago. The crankcase volume changes by nearly one litre at every rev as both pistons go up and down almost together and so breathing is a problem especially when you add to it blow by past the pistons. Any atmospheric breather must be of low inertia (no ball valves) so that it is sensitive to the pulses of the engine up to 6000 rpm or so. Firstly your bike should have good bores and rings otherwise you will be wasting your time. I have blanked off the timed breather and fitted a Kevlar disc valve (low inertia) on the top cap of the front exhaust valve of my twin which is very obscure, out of the way and does not spoil the look of the bike. I drilled holes in the underside (non stressed part) of the exhaust rocker housing and ported past the upper valve guide giving a vent of about half an inch square. The valve housing is the full diameter of the top cap and has eight quarter inch holes in it over which a Kevlar disc is attached. I have blanked off the oil feed to the front rocker as enough oil mist gets up there from the engine which drops out in the large diameter valve cap from which a half inch pipe leads to the back of the bike. All I get from the end of the breather pipe is a little moisture from the products of combustion. QED [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
more on breathers
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