Hitchcocks Forum

Hello, I cleaned my breather box and now I cannot put little piece of duckbill back in. Is there any alternative I can use as a duckbill? Another question: If I ride bullet without duckbill what will happen? Any damage?

One option is to put a non return valve to breather pipe? What else? Any simple solution I can do without big modification?

Peter

The duckbill is a simple beautifully engineered non return valve

Yes it is. The problem is I cannot put it back on. And to get it by post it will take some time. Are any alternatives during waiting time until I get new one?

aaaah, the incredible duck bill.



incredible in a sense that is does the exact opposite of what is is “supposed” to do.



it supposedly is the best invention of the century and for long to come in “getting rid” of to much pressure in the crank chamber.



but in the real world it does the exact opposite.



at least replace it with a bit of tube and something like this in the middle, with a smal air filter ad the end.



and thats a real functioning non return valve, not something made in time long gone by where it was believed that horses spoke, there was gold and the end of the rainbow and everything was better when it was made in good old blighty .

Remove catch can, throw it away, lead new breather pipe up behind battery then down to chain. Fit duckbill to end of new breather pipe. Blank off catch can drain that returns to behind the timing chest. Job done.

Hi Mauri...that looks a very nice device, I wonder what the minimum forward opening pressure difference is? I can imagine that the reverse flow is cleanly cut off which is very good so as long as the opening pressure is quite low it should work very well as a motorcycle breather. You don't need an air filter at the end of the pipe from the valve as the gases being emitted from the engine should be flowing one way (exhausting) from the pipe so there will be no flow back into the engine to worry about....I'll try to find out what the opening pressure is and I'll buy one if it is very low....The Duck bill opens at probably less than 1 Lb. /inch and many on other makes of flap valves open with slightest flow but perhaps don't shut too well...(note some engine designs use a mechanical driven valve Norton Domis for example.) Biggest problem with most breather valves is that they are usually very small diameter that cannot pass the high pulse rates of gas quickly enough. In theory any amount of crankcase gas expelled as the piston/s fall should result in a lower internal pressure when the piston rises back up again. This lowering of pressure or vacuum creation reduces the chance of oil leakages, however, any piston blow by will nullify the slight vacuum created so a constant discharge of gas is required to maintain the vacuum. Using a breather pipe without a valve is a waste of time mostly as the engine just tries to pump gas in and out and therefor achieves nothing.....Les

Perorec



I'm intrigued to know why the original short duckbill from the breather can won't fit back on...



The sort of non-return valve suggested by mauri works well enough as an alternative to the duck bill, I'm using two different types (same principle) on my set-up as there's also a rocker breather line in the system. My breather system is deliberately over-specified (!) and probably not what you want, but it gives you some idea.







A.

Adrian, are you actually running a magneto on that or is it a fake like mine was. As I can't see your primary case I can't see if the pulse coil is still fitted. Nice setup you have

Very nicely demonstrated Adrian....Les

Adrian


I cannot put it back on in breather box. It doesn't fit. Seem like duckbill shrinked. I don't know..... I gues as is ten years old rubber got harder? And now I cannot pull it back on? That round piece of duckbill is quite short soon it start to flatten. So when I put it back on its round base doesn't hold strong enough that piece in breather box where should fit. And its flatten part I cannot pull over. Round base of duckbill is too short to hold it and no way to put it a little more on because of flatten part.