So the "improved" 850 breather is identical to an emissions-era auto breather without the PCV valve - primarily it keeps oil vapor out of the atmosphere, oil drips off the concrete while keeping the crankcase pressure mostly neutral by allowing it to "go" somewhere.

OK, so I can see how the attempt to add a "PCV" valve that can actually react quickly enough to the change in pressure would be able to provide some negative pressure in the crankcase. After reading about the different Norton breathers, I couldn't see how that could work with what I understood as the "timed breather."

MexicoMike wrote:So the "improved" 850 breather is identical to an emissions-era auto breather without the PCV valve - primarily it keeps oil vapor out of the atmosphere, oil drips off the concrete while keeping the crankcase pressure mostly neutral by allowing it to "go" somewhere.

OK, so I can see how the attempt to add a "PCV" valve that can actually react quickly enough to the change in pressure would be able to provide some negative pressure in the crankcase. After reading about the different Norton breathers, I couldn't see how that could work with what I understood as the "timed breather."

You would want to block off a timed breather if you used a valve breather.

You have to remember that as much volume change occurs below the pistons as above them and it takes holes the size of the carburettors and exhaust pipes move that volume in or out so a little hole like the one on the end of the cam with the timed breather is pretty useless. The way CNW does it is as good as can be done within limits, punching big holes in the crankcase would not be good for strength. Probably the best thing to lower crankcase pressures would be to use an offset crank.

Jean

It seems to me as the pistons continue their cycles there would be less air to move as it would start to work in a slight vacuum, This would decrease the amount of air that needs to move on the next stroke. Remember air can get out but not back into the crankcases. I think this is why even a small XS650 valve helps some, This is just how my little brain sees it. LOL

Hortons Norton wrote:It seems to me as the pistons continue their cycles there would be less air to move as it would start to work in a slight vacuum, This would decrease the amount of air that needs to move on the next stroke. Remember air can get out but not back into the crankcases. I think this is why even a small XS650 valve helps some, This is just how my little brain sees it. LOL

I guess it would work that way if air had no mass, but it does and in a small pipe, the air would move less and less as the frequency of the pulses went up so the idea is to place the valve as close as possible to the crankcase with the biggest pipe possible but not past the capacity of the valve.

Jean

Vacuum has no mass.