Author Topic: Ignorance : PHOTO ADDED Why A10/A7 engines have no breather pipe?  (Read 968 times)

Offline Peter Gee

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I have seen a few folks fit a gooseneck pipe and extension  rubber pipe to the breather exit on the drive side c/case outlet, but it seems it was not the practise from the factory. I am soon to start my 59 A7SS rebuild, and although I intuit that the BSA breather system  is novel compared to other twins, I can't see why I won't get  at best an oily mist exiting from the breather outlet, blowback of the same at speed and a general mess?

Enlightenment awaits me, I hope.

Offline Swarfcut

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Pete, for what it's worth an evolution of design and cost cutting.  A7 Longstroke and the early Plunger cases share the same breather external pipe, depositing oil mist onto the chain (via a small bleed hole) and onto the road and garage floor as the pipe was originally secured to an engine through stud behind the sump plate. Late Plunger engines have a small pipe directing breather mist to the gearbox sprocket, anchored beneath the flat alloy  extension/chainguard front mount.

 With the advent of the S/A engine, some retain the same type of early pipe, exiting down by the sump plate, later ones just have a hole, presumably as the engines could be fitted in frames with a fully enclosed chaincase and the pipe would be in the way. The oil mist lubricates the fixed front chainguard section, which is why many survive.....or because lots were removed.

 Your option is to enjoy the oil and muck of yesteryear or counterbore the hole for a spigot and add a flexible pipe to allow oil mist to lubricate the chain or  just drip.

 Swarfy.

Offline Peter Gee

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Thank you Swarfy, however, am I correct the location of the breather outlet is: drive side crankcase, below the boss that is for the non-driven end cam journal? If you reach down with a finger just   the primary chaincase  "gap" with the crankcase, you can feel  the hole?

If so it takes a standard BSP copper pipe..perhaps with a dab of JB weld..one could add a little  spigot. Have not yet started the engine so it should be fine and dry  to take the JB Weld. Thanks again


Offline Swarfcut

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Pete, yes, that's the one. The hole is a shade over 8mm diameter and runs straight up towards the cam bush for 65/70mm.  Any tube introduced into the hole will obviously offer a restriction. A thin walled tube may be too flimsy to survive the engine vibration, hence a suggestion to counterbore  for a spigot, which allows the original 8mm bore to be maintained.  But sod that, JB Weld and a  beer can sleeve as a quick experimental remedy? A steel roll pin would also do if you can find one. Maybe I am a bit cautious about restricting the hole...a copper tube was originally used, just sealed into the hole and well supported, this proved adequate at the time. Plenty of pictures on the Forum to show how other folks have modified the outlet to catch the drips.

 Swarfy.

Offline Greybeard

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Peter, why are you worried about the breather. It seems to do fine the way it is on most of these engines. The position of the outlet does give the chain a drink.

Offline Peter Gee

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Greybeard, because the outlet of the breather is simply a hole in the back of the drive side crankcase. Ig hot oil mist is coming out of it, it will give many more parts of the bike a drink IMO.  Not having had an A7/A10 before, I simply don't know how that arrangement of a plain hole behaves when under way.

Every bike I have ever owned besides a japanese total loss had a breather pipe going down under the bike....this is exactly what someone has done here

Offline Greybeard

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My engine does have a pipe stub in that hole. It's pointing toward the drive sprocket.

If the engine is in good order and if it's not ridden like it's stolen, the breather will not produce much, if any, oil.

I am not aware of anything coming from the breather on my bike; there is no sign of oil dripping from that area after any length of ride. I actually need to lube the chain once in a while.


Offline mugwump

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I've owned many cars from the 1960's and a crankcase breather pipe open to the elements was the norm. Trouble was the burnt oil residue tended to enter the car though!

60'Matchy G12
58 AJS 18s
58 Ariel Huntmaster]

Offline Peter Gee

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GREYBEARD: That you have zero oil coming out of that breather hole is very interesting. It shows the BSA design was excellent compared to many. I think I will install a gooseneck copper pipe anyway..with rubber hose..this is a concours rebuild and nothing like a few drops of oil to lose one a prize, after a lot of hard work.

On another matter I indeed fitted the sandwich old Payen head gasket from the batch I have.. amazing how much re-torquing they need.. always a bolt of two looser.Have not of course run it..am going to retorque ver the next few days till these is no more give in any of the 9 bolts before I do. I hate messing with rocker boxes!  Enjoy the weekend.

Online trevinoz

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It is a good idea to fit a tube into the breather outlet, especially when starting with a full sump.
Without a tube, oil goes everywhere, with a tube it can be directed into a container.

Offline Swarfcut

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Pete, I see you have found the earlier thread about the breather. Apologies for repeating myself here, but while I thought it familiar, I had forgotton  my contribution to that thread.  Looks to be the start of "Maturity Onset Aytentia,"** one of the classic symptoms. I reckon you folks can list a few more of this affliction, enough to start a new topic.

 Trev.. A timely reminder to reach for the big bowl when you find the oil tank empty and you can't be arsed to drain the sump.

Swarfy.

 ** Aytentia... A state of mind brought about by too much attention to other folks A10 Problems......A10 (Demen)tia.

Offline BSA_54A10

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    • BSA National
If you get your hands on period publications you will see that the tube used to fall out and get messed up in the chain.
The plain hole does not do this.
Also unlike the Japanese engines this breather is timed so apart from reversion nothing goes into the hole
Bike Beesa
Trevor

Offline RogerSB

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1960 A10 - no pipe (photo taken using a small inspection mirror).

1960 Golden Flash

Online trevinoz

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Swarfy, no bowl is big enough and the stand gets in the way.

Offline berger

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if your unlucky like I was and its wet sumped enough you don't only get it all over the floor but also blown past the maggy seal and an oil cooled mag is the result *eek*