The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Signboy on 07.11. 2016 07:40

Title: engine breather (again)
Post by: Signboy on 07.11. 2016 07:40
Guys, still having problems with engine breather,  just cant get used to the amount of oil dripping from the breaher pipe, surely, it cant be right.  my bike is a 1953 plunger star twin, the engine breather faces forward just behind the primary chaincase , this ,when im motoring, distributes oil backwards all over the underside of the engine, then, when parked up, continues to drip into a small pool of oil about 2" in diameter ( not so much when on the main stand )
Some of the previous fixes suggest putting a tube from the breather and routing it through the back of the primary chaincase or to drip onto the chain.......my question is, would it be possible to "vent" the two inlet rocker covers to prevent the pressure building up in the first place ?
has anyone else done this ? did it work ?or will i wreck the motor by doing this ?
atb
Robin Watson
Title: Re: engine breather (again)
Post by: Klaus on 07.11. 2016 08:30
Hi Robin,

A huge amount of Oil coming out from the breather is not normal.

First be sure that is not causing in wett sumping. If the oillevel in the crankcase rise up by a longer stay the enginge spit off the oil over the breather. If the bike is in permanent use this willnot happend.

Standing on the sidestand can be also Gearbox oil, or the breathertube is running out.

Check your corkwasher behind the breather valve. If there is much play, also oil coming out, by not sealing the rotaion valve.
There had to be no play in axial direktion.

Befor you think about any other steps in direction ventilation over the rockerbox, please control that.


cheers Klaus
Title: Re: engine breather (again)
Post by: muskrat on 07.11. 2016 08:48
I agree with Klaus. The cork seal should be thick enough to hold the cover off it's mate by about 1/2 mm. If the seal is good and the oil pump is scavenging properly there should be very little oil coming from the vent.
If the motor is wet sumping and your only riding around the block, the pump doesn't have time to clear the sump (can take up to 10 minutes). When running there is only a cupfull of oil in the motor.
Cheers
Title: Re: engine breather (again)
Post by: Signboy on 07.11. 2016 20:38
Thanks for the prompt replies guys... got to say this leak is only after a good sustained run at speeds over 60mph !! i got the bike a year ago and have receipts from SRM who built the motor for the last owner in 1986 !   he only did 400 miles on it, stood in a garage till i bought it  ive done 1500 miles on it in 6 months !      might it be the little cork flappy thing has shrunk or something ??
anyhow, thanks again
Robin Watson
Title: Re: engine breather (again)
Post by: Klaus on 07.11. 2016 21:15
Hi Robin,

30 Years is a long time, and yes it can be the cork is shrunk, also the pistonrings can clued from oil by the long storage.
It seems the engine running hot over 60 miles, so have a look at the ignition timing,and  may be offset in timing. I have seen camrings with 6 degrees offset that meens 12 at the crank. Timing and control always  with a strope.

cheers Klaus
Title: Re: engine breather (again)
Post by: KeithJ on 28.11. 2016 22:26
I have a similar problem.  I have just rebuilt my engine with roller main.  I have renewed mains, big ends, new pistons, rings, rebore, guides sleeved, etc.  Also checked the end float of the breather cork washer and it still drops too much oil out of the breather.  It does wet sump, had about two or three cupfulls after a couple weeks.  Any suggestions appreciated.
Title: Re: engine breather (again)
Post by: muskrat on 29.11. 2016 09:56
It does wet sump, had about two or three cupfulls after a couple weeks.
G'day Keith.
You lucky bugga. My plunger does that in a couple of days! Only takes 5 minutes to drain the sump (with a sump plate and drain plug) and put it back in the tank. 20 years since the last bottom end freshen up so I'll put up with it till the next one and renew the ball and spring (the only thing not on your list of renewed items).
Cheers
Title: Re: engine breather (again)
Post by: olev on 29.11. 2016 10:59
Has anyone personally fixed the problem of oil coming out the breather by replacing the cork washer?
Shouldn't the centrifugal force on the cam wheel throw any oil away from the area?
and why did BSA leave a big hole in the breather valve that buts against the cork instead of sealing it?
are people sure this is where oil get into the breather?
just a thought,  cheers
Title: Re: engine breather (again)
Post by: KeithJ on 29.11. 2016 11:26
My main concern is the amount of oil coming out of the breather when the engine has been rebuilt.  Not sure what to look at?
I also don't understand why the cork washer appears to be so critical?  if there is no end float on that should be OK?  Back to basics if there is oil coming out of the breather that must be due to too much oil in the crank or too much pressure.  Too much oil means not scavenging enough and too much pressure mean it is not breathing properly.  Any other options?
Just thought, I have fitted an oil filter with a replaceable filter on the return side.  I have now done about 700 miles and it is due to be changed.  That could be it?  I will change the filter and see.  It's good to talk!
Title: Re: engine breather (again)
Post by: bsa-bill on 29.11. 2016 13:58
Quote
I have fitted an oil filter with a replaceable filter on the return side.

not all filters are suitable, you should be able to suck or blow through it without turning blue
Title: Re: engine breather (again)
Post by: chaterlea25 on 29.11. 2016 17:15
HI All,
my €0.02 worth  ;)
The cork washer needs to be compressed, If you can move the breather on its peg with your  fingers then its too loose! fine adjustment can be achieved by sanding the thicker cork washers to size
The hole in the breather top hat is for the drive peg and should not affect the breather

A newly rebuilt engine may not have achieved full ring sealing and some blowby will occur till the rings are fully bedded in

As the filter is on the return line it should not effect the oil circulation unless it has been connected back to front *eek*
the feed goes to the outside of the element, centre to oil tank

I do not like the idea of sleeving guides on aircooled engines ! I have seen too many fail *sad2*

John
Title: Re: engine breather (again)
Post by: KeithJ on 29.11. 2016 17:22
The cork washer needs to be compressed, If you can move the breather on its peg with your  fingers then its too loose!
I don't understand why?  Everyone says so but as long as there is no end float, why does it have to be compressed so much?

Title: Re: engine breather (again)
Post by: RichardL on 29.11. 2016 17:56
I think part of that must be so that it doesn't get thin-beyond-useful when the breather actually starts spinning.

Richard L.
Title: Re: engine breather (again)
Post by: KeithJ on 29.11. 2016 18:16
It can still have end float without having lost the drive to the breather?
ATB
Title: Re: engine breather (again)
Post by: muskrat on 29.11. 2016 19:06
G'day Keith and all.
When you offer up the inner cover the cork should hold the cover off the case by about 10 to 20 thou to sseal properly.
With 700 miles on the motor the rings should be well and truly bed in unless you were too gentle and glazed the bores. Blow by increases the crank pressure and with wet sumping there's too much oil in there so it tries to escape out the breather. Once the scavenge pump has caught up and you get bubbles from the return pipe the problem should disappear.
So drain the sump, wash the underside of the motor and go for a 50 mile ride and see if she still blows oil out the breather.
Cheers
Title: Re: engine breather (again)
Post by: duTch on 29.11. 2016 19:27

 
 How about a possible bad seal of the small internal joint (in front of and slightly above the camshaft) that the breather gallery passes through?

Title: Re: engine breather (again)
Post by: KeithJ on 29.11. 2016 19:30
Interesting thought.  I will have a look at another set of cases to see exactly what you mean.
Thanks
Title: Re: engine breather (again)
Post by: chaterlea25 on 29.11. 2016 22:33
Hi Keith,
Quote
I don't understand why?  Everyone says so but as long as there is no end float, why does it have to be compressed so much?

Because it has to be air tight!

John
Title: Re: engine breather (again)
Post by: KiwiGF on 30.11. 2016 04:38
Hi Keith,
Quote
I don't understand why?  Everyone says so but as long as there is no end float, why does it have to be compressed so much?

Because it has to be air tight!

John

I'd be interested to know why it has to be airtight? I thought the cork was just to provide an adjustment to stop the drive pin from rattling around? E.g. A bit of a bodged design by BSA.......
Title: Re: engine breather (again)
Post by: KeithJ on 30.11. 2016 08:56
"Because it has to be air tight!"

But it would only be on one side?  If being airtight was critical, surely it would need to be airtight on both sides?

Keith
Title: Re: engine breather (again)
Post by: olev on 30.11. 2016 10:04
Its an urban myth.
Has anyone actually seen with their own eyes that replacing the cork washer fixes oil coming out the breather?
When the pressurised air gets into the breather and the timed port opens, it has to rise 50mm to get into the breather drain.
Surely the only way oil can get in here is as oil mist.
cheers
Title: Re: engine breather (again)
Post by: duTch on 30.11. 2016 10:48

Quote
...But it would only be on one side?  If being airtight was critical, surely it would need to be airtight on both sides?

  If it's not airtight on one side,surely it's prone to be half-not airtight on both sides... *dunno*

 Having said that ^^^, I have to admit, I've quandered this also to an extent *beer* *eek*, but isn't the flow between the outer-case 'tophat' centre hole (not Topdad) and the 'tophat' breather holes??
Title: Re: engine breather (again)
Post by: chaterlea25 on 30.11. 2016 17:41
Hi All
Doubting Thomas's or What  *????* *????*

The top hat flange seals against the inner timing cover on one side and against the cork washer and cam gear on the other
The breather holes are on the cylindrical part and align with the case holes at the appropriate time
The cylindrical  part is a good fit in the case and the oil film should prevent the passage of air
If a very thick cork washer is needed be careful that theres enough of the driving peg protruding to drive the breather  *warn*

Yes I have experienced the difference that a tight fitting cork makes
A few years ago I rebuild an A10, after some mileage it was puffing a bit on the breather and a bit of smoke in the exhaust
A new cork washer sorted it *smile*


John
Title: Re: engine breather (again)
Post by: KeithJ on 30.11. 2016 17:48
"Yes I have experienced the difference that a tight fitting cork makes
A few years ago I rebuild an A10, after some mileage it was puffing a bit on the breather and a bit of smoke in the exhaust
A new cork washer sorted it"

Still does not explain why?  How about if there is end float, it allows the drive pin to move in the hole in the breather.  It also allows the breath hole to move in and out.  This makes the amount of "breather hole" be reduced and less breathing? 

What would happen if the hole was made into a slot?
ATB

Keith
Title: Re: engine breather (again)
Post by: chaterlea25 on 30.11. 2016 18:03
Keith, AKA doubting Thomas

(Basically) The breather is closed during the piston up stroke creating a partial vacuum in the crankcase
this vacuum helps hold the oil inside the engine
If the breather is loose the engine puffs in and out as it rotates = oil leaks

There are some people who modify the breather sleeve holes to increase the open period
Its not an answer to other engine issues that increase crankcase pressure (worn bores ,rings and valve guides)

The hole on the drive flange of the breather is only for the driving peg, its not part of the air passage
Its effectively sealed  when the engine is assembled

John
Title: Re: engine breather (again)
Post by: KeithJ on 30.11. 2016 19:12
I understand the movement of the pistons up causes a vacuum which should minimise oil leaks.  So if the engine has good pistons, bores and valves etc, then, the pressure to be released on the down stroke needs to be released, hence the timed breather.  I guess this is set to just after the power stroke to just after BDC non the upstroke.

Still don't understand why the cork washer is so critical?  Surely, all it does it to keep the breather and driving peg in a fixed position relative to the breather drilling?  The clearance between the breather and the inner timing cover would also impact the vacuum
 
Perhaps mere mortals such as me are not meant to comprehend such matters?

ATB

Keith
Title: Re: engine breather (again)
Post by: KiwiGF on 30.11. 2016 19:39

Perhaps mere mortals such as me are not meant to comprehend such matters?

ATB

Keith

The timed breather does have a little more to it than the obvious  *doh* *doh* (there are high speed pressure fluctuations going on, with "inertia" of gases being required to move quickly etc, akin to the mysteries of megaphone design) and I think it best to ensure the cork thickness is sufficient to prevent end float of the breather as pretty clearly BSA in tended that to be done, as to whether a breather with endfloat (and leaking) does not work as well as one without? I doubt anyone can conclusively say why that would be the case  *dunno* there may be theories about the outer case having different pressure to the inner case area, but that's what they would be....theories  *fight*

On my bike I had to use such a thick piece of cork I had to extend the breather drive pin length as beforehand it was slipping out of engagement, I guess the case had distorted over time  causing this *dunno* anyway I doubt this is unique to my bike and indicates that having a good look at the breather and making sure it is set up right may very well solve an issue with excessive gases coming out of the breather tube, but a friend of mine spent numerous hours solving his issues in this area (excessive case pressure causing the crankshaft oil seal to pop out), what ultimately fixed is a bit inconclusive, maybe the new valve guides? Rebore? Fitting a modified BSA breather (elongated holes in the breather to change its timing) instead of the bunn? On that last mod, this may be worth you trying..........
Title: Re: engine breather (again)
Post by: chaterlea25 on 30.11. 2016 19:59
Hi
Quote
The clearance between the breather and the inner timing cover would also impact the vacuum

When the case is bolted up and compresses the cork washer there is zero clearance between the breather flange and inner case !

Kiwi,
If the case was bolted up without aligning the peg and breather it may have damaged the case ???
Worse if it was run like that, or with a too tight preload and worn the alloy case ????

John
Title: Re: engine breather (again)
Post by: olev on 30.11. 2016 21:30
hmmm, I hadn't thought of the oil coming into the breather arrangement past the tophat bearing surface.
I assumed oil somehow got inside the top hat and was slung or pushed up the timed output hole.
or the oil arrived as a vapour and condensed inside the tophat and the outlet drain.
Maybe its possible the breather system is working within specs but just overcome by extra oil being slung into the area by the timing gears.
Maybe once oil gets into the outlet it increases the resistance to air flow and compounds the problem.
Maybe some modern oils create a denser oil mist when stirred up by the timing gears and this gets into the breather system.
Maybe I'll just stop thinking about this and go and get on the p!ss.
cheers
Title: Re: engine breather (again)
Post by: RichardL on 30.11. 2016 21:52
I think, maybe, we don't need to talk about any relationship of close timing between up and down piston movement and hole alignment in the breather. The hole is only aligned every other crank rotation. I can't believe it's been almost ten years since I mocked this up to see what was going on, so my memory may be weak, but I believe the breather is open at 90 deg ATDC. I have guessed, right or wrong, that the breather is trying to keep crankcase pressure as close to one atmosphere as possible so that oil can be pumped in and sucked out. This may disagree with those who believe (or know) that there is some performance benefit based on where in the stroke the breathing occurs. By my theory, such benefits (or detractions) would be purely coincidental with respect to BSA intentions. (I can be wrong and often have been.)

Then there is the matter of why a lot of oil spills out when there is substantial wet sumping. Seems to me it is way too much to get in from the back side past the flange. That means it would need to enter past the tapered end in the portion contained by the outer cover. There is an oil drain hole that could allow this. So, it seems that the wet sumping would have to fill the crankcase about up to the height of the breather for oil to get in through the breather's open end. (Waiting chastisement for silly or "Richard, are you just now realizing this?" Well, not quite just now.)

Richard L.
Title: Re: engine breather (again)
Post by: KeithJ on 30.11. 2016 22:24
Just looked at a breather and it has two holes in it 180 deg apart.  So it "vents" every revolution.

AtB

Keith
Title: Re: engine breather (again)
Post by: duTch on 30.11. 2016 22:38

 Yep, as it needs to
Title: Re: engine breather (again)
Post by: KiwiGF on 01.12. 2016 02:21
Hi
Quote
The clearance between the breather and the inner timing cover would also impact the vacuum

When the case is bolted up and compresses the cork washer there is zero clearance between the breather flange and inner case !

Kiwi,
If the case was bolted up without aligning the peg and breather it may have damaged the case ???
Worse if it was run like that, or with a too tight preload and worn the alloy case ????

John

There was no evidence of wear on the case, but it's difficult to tell, there was evidence of the peg wearing the breather, but nothing too serious so I guess the peg wore away pretty quickly. The bike was a basket case pretty much when I got it and I never ran it like that, I noticed the problem when building the engine up.
Title: Re: engine breather (again)
Post by: duTch on 01.12. 2016 03:20
 
Quote
Its an urban myth.
Has anyone actually seen with their own eyes that replacing the cork washer fixes oil coming out the breather?

  This may well be a mighty fine opportunity to find out...."suck 'n See" *smile*

 I'm not sure if I needed to actually do it, but at least considered packing a too-thin cork with gasket paper behind (sneaking suspicion I did)
Title: Re: engine breather (again)
Post by: RichardL on 01.12. 2016 06:34
Uuuuugh! It's been a long time since I looked at that damn breather and have embarrassed myself again. So, anyone care to comment on my claim of neutral pressure versus tuning for pressure? I may as well have a thorough stropping, no reason to go half way.  Next time I'm just claiming old age and leaving it at that.

Richard L.
Title: Re: engine breather (again)
Post by: KeithJ on 01.12. 2016 08:37
Doesn't the cork washer also cut take out the end float on the cam shaft?  Or have I misremembered?
ATB
K
Title: Re: engine breather (again)
Post by: duTch on 01.12. 2016 09:01

 
Quote
Doesn't the cork washer also cut take out the end float on the cam shaft?........

 Emphatically NOT... *bash*

Quote
  Or have I misremembered?
     Yep

 Set the Cam end float independently, and when I did mine, I put the barrels on blank (no lifters/followers/"tappets") and look down the pushrod tunnel to check for centrality.
 Then do the other thing whatever we're on about