Author Topic: What is it (breather on tappet cover?)  (Read 1910 times)

Offline stevejs

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What is it (breather on tappet cover?)
« on: 27.11. 2018 15:59 »
Any of you clever people know what this is for? It's on the inlet tappet cover on my 1954 A7SS. Some kind of breather??

Offline Topdad

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Re: What is it (breather on tappet cover?)
« Reply #1 on: 27.11. 2018 16:13 »
yep , it's a breather fitted in the hope it helps fight oil leaks ,just read an article which said it can do the reverse ,I've done one on my inlet cap and honestly cant see any difference .cheers Bob
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Re: What is it (breather on tappet cover?)
« Reply #2 on: 27.11. 2018 16:55 »
Got one on my A10. Roger at Cake Street blocked it off when he rebuilt my motor - I think he took a dim view.
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Re: What is it (breather on tappet cover?)
« Reply #3 on: 27.11. 2018 17:27 »
Physical evidence of desperation.
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Offline berger

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Re: What is it (breather on tappet cover?)
« Reply #4 on: 27.11. 2018 18:57 »
I have not been to the pub, that sort of breather on the inlet can pull extra air down worn valve gear and confuse you when setting up a carb

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Re: What is it (breather on tappet cover?)
« Reply #5 on: 27.11. 2018 19:01 »
G'day Steve.
As said it's for a breather. I have one on my Cafe with a Bunn breather (one way valve) and another on the engine breather behind the primary. Fresh air goes in at the top and smelly air comes out the bottom. Sort of like us!
Cheers
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Offline BSA500

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Re: What is it (breather on tappet cover?)
« Reply #6 on: 27.11. 2018 20:17 »
Mine had the effect of clearing the creamy oil emulsion from the rockerbox. Didnt matter how hot the engine got it was always there,not now *smile*

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Re: What is it (breather on tappet cover?)
« Reply #7 on: 27.11. 2018 22:17 »
Quote
the creamy oil emulsion from the rockerbox

Never seen any of that on my bikes - on Mini's I had oh yes
All the best - Bill
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Re: What is it (breather on tappet cover?)
« Reply #8 on: 28.11. 2018 02:45 »
 
Quote
.Mine had the effect of clearing the creamy oil emulsion from the rockerbox......
  Generally means a presence of water/ moisture- I had a heavy presence of that recently in my Ute slow head gasket leak (obviously won't be a cause on a BSA, but .ca be sucking it in through the covers., ore just condensation buildup if not often used...

 
Quote
....Fresh air goes in at the top and smelly air comes out the bottom....

 I always figured the breather just expels excess buildup of the air already in there by default.... and doesn't need any extra....*dunno*/ *conf2*
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Re: What is it (breather on tappet cover?)
« Reply #9 on: 28.11. 2018 06:02 »
I have always wondered where the breather is located on my A10. Could someone enlighten me please.
I assume it is working as I don't suffer (excessive) oil leaks but I have been told by very knowledgeable persons that my engine would benefit from an extra fitted breather. What is the general opinion on this one?
Cheers, Hadrian.


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Re: What is it (breather on tappet cover?)
« Reply #10 on: 28.11. 2018 06:23 »
Nah. The designers did well enough. If your bike's breathing is inadequate, something's not right. 
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Re: What is it (breather on tappet cover?)
« Reply #11 on: 28.11. 2018 07:38 »

 
Quote
I have always wondered where the breather is located on my A10. Could someone enlighten me please........

 The exit hole is under the boss of the left end of the camshaft,  behind the chaincase and  in front of the magneto end cover
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline BSA_54A10

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Re: What is it (breather on tappet cover?)
« Reply #12 on: 28.11. 2018 20:33 »
Nah. The designers did well enough. If your bike's breathing is inadequate, something's not right.

Actually this is one time when they did not .
The factory breather really only works well up to 1/3 throttle, barely works to 2/3 throttle and works backwards over 2/3 throttle.
Rex did a lot of work before he handed the project over to Auckland University where they did extensive testing revealing the above.

Now the caveat to this is the bulk of the time we ride at 2/3 throttle or less so it will do, although it could be better.
Weather it is worthwhile to muck around with breathing depends very much on the rider.
If you are WFO type of rider ( ie Musky ) then it is worthwhile and will substantially reduce leaking & oil burning.
On A7/10's proper breathing will end the infamous rocker box leaking that bedevils a lot of owners.

The idea of creating a partial vacuum in the crankcase comes from the days of long stroke engines that had no oil seals and had a rev ceiling in the order of 5000 rpm.
Thus the engine was designed to perpetually suck air in through all of the slingers & blow it out the breather past an unsprung almost one way valve.

Crankcase venting is every bit as complicated as induction breathing and exhaust tuning.
As such it is very difficult to design  system that will work properly all the way from idle through to valve bounce.
The through flow design with check valves is the only system that has the ability to work over the entire rev range.
No mechanically timed system can work properly over the entire rev range because air has mass and therefore there is a latency and momentum effect which gets more pronounced the higher the revs.
On the A 10 tested near 1.5 Hp is gobbled up by the ineffective breathing system at peak revs.

Now back when the bikes were new, leaving a puddle of oil on the ground after a good "high spirited" ride was acceptable .
However leaving a pool of oil when at idle on the showroom floor was not.
Thus a breathing system that works best just off idle.
Bike Beesa
Trevor

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Re: What is it (breather on tappet cover?)
« Reply #13 on: 28.11. 2018 23:09 »
Well, you live and learn!

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Re: What is it (breather on tappet cover?)
« Reply #14 on: 29.11. 2018 06:28 »
I'm still not going to mess around with the breathing on my bikes. 46 years of good service and hardly an oil drip is good enough for me.
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