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Breathing Mystery

Hi Everyone. I've just completed an engine rebuild on my WM20 and the engine is now running sweetly,apart from an unusual wheezing/whistling noise which i've tracked down to air being forced up the hole in the cylinder between the exhaust tappet and the stud/nut in the tappet compartment,it is then forced out around the cover and the exhaust lifter causing the noise. The engine breather is clear and appears to be working normaly. Any ideas please.

email (option): michaelggilbert@btinternet.com

Re: Breathing Mystery

i am not sure but 2 things come to mind 1 have you got the valve in the crankcase breather just above the primary chain case the right way round then there is another type of engine breather which is to do with the mag drive cog which has a hole in it and time the breather which have the breather on the timing/cam cover this may be on later BSAs

email (option): roger.beck@node6.com

Re: Breathing Mystery

It could just be that the piston rings haven't bedded in yet so there is a little bit of blow by on the piston rings, this will create a bit more pressure in the crankcases

email (option): davmax@ntlworld.com

Re: Breathing Mystery

Thanks Guys, I hav'nt changed the breather and i can blow through it so i assume it's ok. The breather on the timing gear is later, i had one on my A10. I hope it is the piston rings bedding in, maybe i'll just ignore it, ride the bike and hope it goes away.

Re: Breathing Mystery

Are you blowing it in the right direction? Is the hole for the breather attachment into the crankcase clear? Doesn't sound right to me even if the rings are new? I suppose there might be a little pressure there to lubricate the valves with oil mist but for it to be that pressurised ?

Re: Breathing Mystery

Hi Douglas. I have removed the breather and i can blow through it in both directions. I have also attached a pipe to the end of the breather pipe and i can blow directly into the crankcase. I remain flummoxed. Mike.

Re: Breathing Mystery

That sounds like the problem! There should be a one way valve in the breather. You should only be able to suck the air through the breather. It should give you a red face and bulging cheeks if you try to blow through it. I think you should check the components of the breather valve. Ron

email (option): ronpier@talk21.com

Re: Breathing Mystery

Yes..there should be a small tufnol disc in the breather which acts as a flap valve. It is blown off its seat by the downwards movement of the piston, venting the crankcase.
On the upward stroke it should be sucked onto its seat,sealing the valve and creating a partial vacuum in the crankcase. This reduces the amount of air that needs to be displaced from the crankcase on the next downward stroke...Ian

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