Author Topic: Timed breather, what is the actual timing?  (Read 3111 times)

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Re: Timed breather, what is the actual timing?
« Reply #45 on: 23.02. 2020 09:08 »
G'day Sf.
Don't touch it. The breathing is through the top hole and exits on the other side of the motor.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
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Offline Swarfcut

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Re: Timed breather, what is the actual timing?
« Reply #46 on: 23.02. 2020 10:07 »
SF.. Like Musky says....DON'T TOUCH IT!   That's how it it should be.  The lower blanked off hole in the inner timing case is simply where the casting was drilled to form the breather duct. So that answers the second question. Following the duct across the crankcase, the drilling exits above the gearbox sprocket, and should be a free flowing unobstructed path for crankcase vapours.

  The question is how does it work? Well, goodness knows, but it does.  The breather sleeve rotates at half engine speed, located and driven by the peg on the cam drive gear. Pistons rising and falling together will produce alternate high and low pressure within the crankcase. At some point the breather holes align for a fraction of a second, connecting the crankcase to atmosphere, and in theory the engine "breathes." That's it, a minor miracle.

   Things to remember.

    The cork washer that fits between the breather sleeve and the cam gear pushes the cam towards the drive side, in effect eliminating cam end float. It pushes the breather sleeve towards the timing side and should be in light compression when assembled, to keep the cam and breather sleeve in their respective places. It is available in various thicknesses to suit variations in the parts. Too thick will put too much load on the breather flange, and it will wear away itself and the inner timing case. You may find a witness mark. Too thin and the sleeve and cam can float, and the breather won't work properly because the holes will not align fully.

  The holes in the breather sleeve should line up perfectly with the holes in the inner cover. Worth checking, I have come across breather sleeves that only half match the holes. Also the breather sleeve design changed  slightly over the years, but seems to have little  improvement on its function. Whether this is the position or size of the holes is just a guess, so to recap, check the breather sleeve you have matches your timing cover. The drive pin on the cam gear needs to be long enough to ensure a positive drive to the breather sleeve.

 At best it is simply a design for everyday use, tuned and race engines need a better system as detailed elsewhere.

 Apologies to those folks who know this old news, but I can bet a good few wonder how it works.

 Swarfy.

Offline Superflash

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Re: Timed breather, what is the actual timing?
« Reply #47 on: 23.02. 2020 10:52 »
Thanks for the explanation. The problem I have is that I've never actually seen a complete running A10 in the flesh so figuring out how things work or where they fit into the greater scheme of things has been a real eye opener and a bit of a buzz if I'm honest. Cheers
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Online chaterlea25

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Re: Timed breather, what is the actual timing?
« Reply #48 on: 23.02. 2020 16:08 »
Hi All,
A minor correction to Swarfies post (my opinion)
The cam endfloat is limited by the timing gear,
ok the breather/ cork pushes against the gear, the reason being is to form a seal between the rotating top hat and the inner case
It needs to be airtight for the breather to work as designed

Owners blame the breather when there are other engine problems

John
1961 Super Rocket
1963 RGS (ongoing)

Offline Swarfcut

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Re: Timed breather, what is the actual timing?
« Reply #49 on: 23.02. 2020 17:21 »
 John  This is my reasoning, and yes, the poor old breather does get the blame. Cam endfloat depends on the bushes, accuracy of casting machining plus individual parts tolerances.

    The cam is supported on two identical top hat bushes, and a third  bush in the drive side case.  The cam can move sideways to the timing side, restrained by the top hat of the inner bush contacting the shoulder on the camshaft. Movement towards the drive side is restrained by the underside of the timing gear contacting the top hat of the outer camshaft bush. So, without the inner cover, breather sleeve and cork washer, the cam has some freedom of axial movement. This is prevented entirely by the compression force exerted by the cork washer, effectively eliminating any float by keeping the cam firmly pressed towards the drive side, the sideways load acting on the outer bush and underside of the timing gear.

 The breather sleeve is effectively open at both ends. OK, there is a dividing wall in the middle, but this has a central hole, so you could say that crankcase fumes can enter from either end. The critical factor is not so much an airtight seal against the cam gear, more the necessity to ensure the holes in the breather always coincide with the hole in the timing cover as the breather sleeve rotates. This is done by compressing the cork washer, pushing the sleeve into place against the cover, preventing any sideways movement and effectively locates the breather sleeve and cam. 

    If my reasoning is correct the breather should work just as well with a compression spring substituted for the cork washer, pressing breather sleeve and cam towards their respective locations. The drawback here is that more oil rather than fumes could be drawn out, as the standard arrangement is a bit of a labyrinth to allow elimination of gas rather than liquid, so what we all consider to be an airtight seal is in fact more of an oil tight one.

 Swarfy

 

Offline BSA_54A10

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Re: Timed breather, what is the actual timing?
« Reply #50 on: 23.02. 2020 19:02 »
The problem with the time breather is it has a fixed timing.
Air has mass so there is a latency between when the piston starts to move and the crankcase vapour are sufficiently pressurized to start them looking for an exit.
The timed breather is only correct over a specific range of engine revolutions which funny enough are just above idle where crankcase leaks and blow by will be most obvious.
From then on it gets progressively out of sync with the pressure pulses .
It is exactly the same as engine porting in two- stroke engines and why variable port timing ,  (which everyone seems to understand just fine) produced such a massive expansion of the power bands.
Secondly the breather is another exhaust, and apart from the need to remove heat everything that applies to engine exhausts applies to engine breathing and this is where BSA made their big mistake in not taking the effort to work out the correct length for the vent tube .
If the vent tube ends at a pressure pulse node then it will *** out oil .
If it ends at an anti-node it will be bone dry .

Bad breather timing is a big contributing factor to ring flutter at high revs ( normal Musky riding speeds ) which is a big contributing factor to blowing all of the oil out the exhaust pipes when traveling for long periods with the throttle WFO.
The latter was the prime cause of A 65's throwing rods in the USA where there are lots of flat out riding roads and a to a lesser extent in Australia.
Because UK roads are narrow , slow & full of bends & corners these problems did not become apparent to BSA ( or any other motorcycle maker ) till it was way too late.
Bike Beesa
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Online chaterlea25

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Re: Timed breather, what is the actual timing?
« Reply #51 on: 23.02. 2020 19:19 »
Hi Swarfy,
Same coin different sides? LOL
Without the gear the cam can move a long way towards the drive side

A spring would kind of work but would allow oil from the inner gear case out through the inner centre  hole of the top hat, the cork washer effectively blocks that side so the case pressure has to make its way to the outer chamber and back in through the outer end of the top hat
Later Gold Stars have a similar system where the top hat is in the outer cover and spring loaded against the magneto gear, its location at the top of the timing case is furthest away from the oily bits probably helps separate the air from the oil
I know that any looseness in the "A" top hat causes oil to leak out the breather
I aim to get the top hat tight enough to make radial movement  (to and fro against the driving peg) difficult with finger pressure but easy with pliers
New cork washers seem to settle over some time and may need replacement or packing out with gasket material

John

1961 Super Rocket
1963 RGS (ongoing)

Offline Slymo

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Re: Timed breather, what is the actual timing?
« Reply #52 on: 24.02. 2020 03:26 »
Mine smoked and blackened the oil and had brand new pistons and rings. Finally replaced the rings with Gandini ones assembled the top end and bores dry and fired it up. Doesn't burn a drop now and I've done several thousand miles since. seems that if the rings don't bed in straight away they are kaput.
NZ

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Re: Timed breather, what is the actual timing?
« Reply #53 on: 24.02. 2020 08:57 »
G'day Slymo.
Hence my running in program. Just enough oil to let the ring compressor slide. Two laps of the block. Job done!
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7