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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
answers on a postcard please...................
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<blockquote data-quote="Martyn Goodwin" data-source="post: 43731" data-attributes="member: 2433"><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">I finished a complete rebuild of my Comet motor that included muff n liner, new piston n rings, all bearings, new cam, new oil pump etc.– about the only bits not renewed were the cases. In my Comet the timed breather internals have been removed. I have a breather connected to the timed breather outlet with the hose running vertical (well as best as I can get it) to a PCV valve under the tank; from there is a hose that eventually exits at the rear, attached to the rear stand. The importance of getting the hose vertical before the PCV cannot be overstressed; it ensures that the “slug” of oil in the hose can drain back into the cases when the motor is off.</span></span></span></p><p></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">When you think about it, the timed breather is open when the piston is descending, thus trying to pressurise the crankcase and then it’s closed when the piston is on the way up, creating a vacuum in the cases. The pressure/vacuum pulses cause a PCV to do exactly the same thing.</span></span></span></p><p></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">I next, in addition to my timed breather PCV, I fitted a “D”breather above the inlet pushrod tube, again with a PCV valve – the amount of oil coming from the original timed breather PCV fell away to almost nothing, but it sure poured out of the top breather. There is a very rich oil supply around the rockers – because of the convoluted path to the timed breather outlet there is a very poor oil supply to that.</span></span></span></p><p></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">Got to thinking that what I wanted to do was give all the gaskets etc. an easy life to reduce the possibility of leaks developing, so next I turned around the PCV valve connected to the “D” cap. Result is when the piston is on its down stroke, trying to pressurize the cases the “timed breather” PCV opens to relieve the pressure – at the same time the (much reduced) back pressure has the PCV on the“d” fitting firmly closed. On the piston UP stroke when it’s trying to create a vacuum in the cases the reverse happens. The “d” PCV opens allowing air into the cases, reducing the vacuum and the mild vacuum holds the timed breather PCV closed. I have a small air filter on the inlet of the "d" breather PCV.</span></span></span></p><p></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">Now there is NO oil exiting via the “d” PCV and just a small amount via the timed breather PCV. And so far – having covered 800 miles since the rebuild - the motor itself is leak free.</span></span></span></p><p></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">Martyn</span></span></span></p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 43731, member: 2433"] [SIZE=3][COLOR=#000000][FONT=Calibri]I finished a complete rebuild of my Comet motor that included muff n liner, new piston n rings, all bearings, new cam, new oil pump etc.– about the only bits not renewed were the cases. In my Comet the timed breather internals have been removed. I have a breather connected to the timed breather outlet with the hose running vertical (well as best as I can get it) to a PCV valve under the tank; from there is a hose that eventually exits at the rear, attached to the rear stand. The importance of getting the hose vertical before the PCV cannot be overstressed; it ensures that the “slug” of oil in the hose can drain back into the cases when the motor is off.[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Calibri]When you think about it, the timed breather is open when the piston is descending, thus trying to pressurise the crankcase and then it’s closed when the piston is on the way up, creating a vacuum in the cases. The pressure/vacuum pulses cause a PCV to do exactly the same thing.[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Calibri]I next, in addition to my timed breather PCV, I fitted a “D”breather above the inlet pushrod tube, again with a PCV valve – the amount of oil coming from the original timed breather PCV fell away to almost nothing, but it sure poured out of the top breather. There is a very rich oil supply around the rockers – because of the convoluted path to the timed breather outlet there is a very poor oil supply to that.[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Calibri]Got to thinking that what I wanted to do was give all the gaskets etc. an easy life to reduce the possibility of leaks developing, so next I turned around the PCV valve connected to the “D” cap. Result is when the piston is on its down stroke, trying to pressurize the cases the “timed breather” PCV opens to relieve the pressure – at the same time the (much reduced) back pressure has the PCV on the“d” fitting firmly closed. On the piston UP stroke when it’s trying to create a vacuum in the cases the reverse happens. The “d” PCV opens allowing air into the cases, reducing the vacuum and the mild vacuum holds the timed breather PCV closed. I have a small air filter on the inlet of the "d" breather PCV.[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Calibri]Now there is NO oil exiting via the “d” PCV and just a small amount via the timed breather PCV. And so far – having covered 800 miles since the rebuild - the motor itself is leak free.[/FONT][/COLOR][/SIZE] [SIZE=3][COLOR=#000000][FONT=Calibri]Martyn[/FONT][/COLOR][/SIZE] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
answers on a postcard please...................
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