Rocker cover breather

[old53]

My  A10  has been fitted with an additional breather from the rocker cover  with a hose going  down behind the gearbox. I have a spare cover and wonder if there is any advantage in refitting the modified cover. Has any body had issues with crankcase ventilation? 

[bsa-bill]

never have needed this mod, my opinion is that if you need this you need to look elsewhere but that is my opinion many others will disagree.
Might be that the way you use the bike has a bearing on this, folk that like to twist a tail could have a point

[The General]

I've been curious about that myself.
My 62 Super Rocket has a threaded hole with a breather hose in the center of the cap.
Original equipment.
Maybe it was for export models to the States?
Your picture appears to be a mod though.

[muskrat]

G'day Carey,
                    An old mod people used to try to eliminate rockerbox oil leaks. When done it negates the timed breather. If you use it I would suggest you look into the Bunn breather kit (about $70AU). I have it fitted to mine and am very pleased.
Cheers

[bsa-bill]

Don't think it was ever original equipment General but could be wrong

[old53]

Can anyone give me  a clue as (or description) of how the timed breather actually works? I have been looking in the tech notes and have not had any success, maybe my lack of computer skills. 

[RichardL]

Back when my engine was completely disassembled, as a mockup, I placed the timing gears on a table with the breather in place and the position of the breather port marked on the table. That's been a while and I should should have kept better records, but, as I recall, the hole in the rotating breather passes the breather port at 90 degrees AFTDC. By this, I have assumed that the breather is not intented to change the pressure in the crankcase. My take on it is that the breather is only intended to keep the crakcase somewhere around normal atmospheric pressure so that oil can be pumped in and sucked out. If you open a full-time vent, it is always pulsating, to what negative affect, I wouldn't know. However, I assume Mr. Hopwood had an opinion on it or BSA would not have gone to such lengths (no pun intended) to duct the breather out behind the timing cover.

Looking forward to the fifteen corrections to my theory, upcoming.

Richard L.

[RichardL]

Two more things. I should note that my engine is S/A type. Second, I wonder if the timing of the breather is not,indeed, such as to create a slight positive pressure in the crankcase in order to assure a dry sump and explaining why oil return is faster than oil supply. After all, can anyone explain this phenomenon according to the design of the pump? I can't understand it. This theory would opt against a continuous breather.

To the extent I may be taking the common knowledge of others as revelation to me, I apologize in embarrassment and look forward the corrections. Until then I'll basque in in the simple logic of my own thoughts.

Richard L.

[MG]

Richard,
the gears of the return oil pump are wider than those of the feed side, hence they offer a higher flow rate for the return.
It's as easy as that. 

[Hubie]

I could be wrong also, but my A10 has one fitted to it and i believe that it was standard on the super roccket.

Cheers,

Dave.

[iansoady]

Can anyone give me  a clue as (or description) of how the timed breather actually works? I have been looking in the tech notes and have not had any success, maybe my lack of computer skills. 

I'm as puzzled as you - I've never found a description and have looked everywhere I can think of. Mine loses a bit of oil through the breather at highish (say 4,000rpm+) engine speeds which is annoying as it then drips when I stop, leading to rude comments from ignorant modern bike riders (having rebuilt the top end of the engine it doesn't leak from anywhere else).

Oil return to the tank on mine is excellent and there's little oil in the crankcase so it's not wet-sumping.

[trevinoz]

Definitely not a standard fitment on any A10/7.
Trev.