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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
more on breathers
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<blockquote data-quote="Martyn Goodwin" data-source="post: 51055" data-attributes="member: 2433"><p>When I first got my Comet the PO had removed the original timed breather, replacing it with a pipe sans valve to atmosphere from where the magneto should have been ( please do not ask how or why). After I reinstated the magneto and the generator I tried all sorts of contraptions in order to get to a oil tight motor and a breather that did not approximate a total loss system. I had excessive crankcase pressure and nothing I tried seemed to work. I tried elephant trunks, PCV valves, Bunn breathers and a hole lot more.</p><p></p><p>The solution was found after I destroyed a piston thru detonation. I fitted a new liner along with a new piston and rings (and sorted the carb and ignition). This eliminated all of the earlier "blow by" that was causing excessive crankcase pressure. At the same time I installed an original timed breather, modified as recommended by PEI - I opened up the "slot" in the pinion thus giving a longer duration when the breather was open. Being a Comet I have only one piston to worry about. I set the timing of the breather so it opens during the down stroke of the piston, and closes at 2 degrees After Bottom Dead Centre.</p><p></p><p>My timed breather outlet now goes into a catch tank (actually a discarded plastic drink bottle, painted black) and in over 2,000 miles of running there is around a teaspoon fool of creamy emulsion in the catch tank. Oil consumption is so low as to be un-measurable.</p><p></p><p>Just my experience</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 51055, member: 2433"] When I first got my Comet the PO had removed the original timed breather, replacing it with a pipe sans valve to atmosphere from where the magneto should have been ( please do not ask how or why). After I reinstated the magneto and the generator I tried all sorts of contraptions in order to get to a oil tight motor and a breather that did not approximate a total loss system. I had excessive crankcase pressure and nothing I tried seemed to work. I tried elephant trunks, PCV valves, Bunn breathers and a hole lot more. The solution was found after I destroyed a piston thru detonation. I fitted a new liner along with a new piston and rings (and sorted the carb and ignition). This eliminated all of the earlier "blow by" that was causing excessive crankcase pressure. At the same time I installed an original timed breather, modified as recommended by PEI - I opened up the "slot" in the pinion thus giving a longer duration when the breather was open. Being a Comet I have only one piston to worry about. I set the timing of the breather so it opens during the down stroke of the piston, and closes at 2 degrees After Bottom Dead Centre. My timed breather outlet now goes into a catch tank (actually a discarded plastic drink bottle, painted black) and in over 2,000 miles of running there is around a teaspoon fool of creamy emulsion in the catch tank. Oil consumption is so low as to be un-measurable. Just my experience [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
more on breathers
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