Author Topic: Breather  (Read 364 times)

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2935
  • Karma: 67
Breather
« on: 04.11. 2019 21:27 »
My friend was comparing breathers which he has on his shelf.
He found  two different types which are from swinging arm engines.
The most common has the driving peg hole about 25 degrees from the vent and the less common has the peg hole about 45 degrees from the vent.
Do any of you knowledgeable blokes have any details of the change and whether there are different part numbers for the the odd one?
Thanks,
Trevor.

Offline Swarfcut

  • Wise & Enlightened
  • *
  • Join Date: Oct 2018
  • Posts: 1274
  • Karma: 19
Re: Breather
« Reply #1 on: 05.11. 2019 10:36 »
Trev, Here's one to consider.  It has a recessed baffle with a central hole, and a slightly tapered end, facing the cover. Interestingly the two opposing holes don't quite match the holes in the inner cover, so the breather system would never work properly with this one fitted. Anyone with a poorly performing breather....well worth checking the holes all line up to give the best chance of the breather working.

 Anyone tried enlarging/slotting the holes to give a longer time for the breather to be open?

Swarfy.

Offline BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 2055
  • Karma: 32
    • BSA National
Re: Breather
« Reply #2 on: 05.11. 2019 11:08 »
Long Stroke & short stroke ?
Bike Beesa
Trevor

Offline Swarfcut

  • Wise & Enlightened
  • *
  • Join Date: Oct 2018
  • Posts: 1274
  • Karma: 19
Re: Breather
« Reply #3 on: 05.11. 2019 13:30 »
Well, as you're asking, the one pictured above came in a job lot of S/A Parts. So I dug out the one from my basket case Longstroke A7 Motor. 

 This one is slightly different,with a more concave end to the outer edge, rather than the tapered shape. Otherwise they appear identical, pictured side by side (Longstroke on the left) to show no difference regarding the  breather holes and drive peg location. Bear in mind these parts may be the correct ones or entirely spurious.
 Surprisingly neither open the breather vent fully in the inner case. In other words the holes don't match completely and coincide perfectly as you would expect.
   Never noticed this before, but got me thinking. Is this how they all are, and why we get problems?

 Baffle insert is deeper on the S/A breather, 11mm, compared to 9mm for the Longstroke. All other dimensions are the same.

The Longstroke uses timing gears with different timing marks, allowing the use of a common breather on Longstoke and early Shortstroke motors.

 Swarfy.

Online JulianS

  • 1962 A10
  • Wise & Enlightened
  • *
  • Join Date: Mar 2017
  • Posts: 1076
  • Karma: 20
Re: Breather
« Reply #4 on: 05.11. 2019 15:20 »
The breather changed in 1961, see below, but what the difference is not explained.

The breather in my A10 had the holes enlarged so as not to be partially masked when open. Also need to check the joint in the breather passage at the inner timing cover/crankcase. The two do not always match and partially mask the passage.

Online RDfella

  • Wise & Enlightened
  • *
  • Join Date: Aug 2017
  • Posts: 1056
  • Karma: 9
Re: Breather
« Reply #5 on: 05.11. 2019 16:10 »
Presumably the different breather timing is as Trevor has found.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 2935
  • Karma: 67
Re: Breather
« Reply #6 on: 05.11. 2019 20:28 »
Thanks Julian, obviously this explains the difference.
Trevor.