The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: KiwiGF on 16.03. 2016 05:04

Title: Timed breather, what is the actual timing?
Post by: KiwiGF on 16.03. 2016 05:04
I'm asking this on behalf of a friend who has had endless problems with crankcase pressure including the primary side crankcase oil seal repeatedly blowing out.

He has measured the timing (at the crank) of the the timed breather and told me that he got these results below, the question is, are these values "normal"?

Open  90 degrees before bdc
Close 45 degrees after bdc

If anyone has the dimensions of an unmodified breather (hole) I guess that that would also help.


Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 16.03. 2016 06:32
 
Quote
   Open  90 degrees before bdc
                Close 45 degrees after bdc   

 Seems reasonably logical, @ 90 degrees before bdc(90º atdc), the piston will have built enough C.C pressure to blow out, and closing @ 45º abdc (135º btdc) as the piston goes up again will inhibit back-sucking through the gallery. As you say though, maybe those figures are not quite right- *dunno*

 
Quote
primary side crankcase oil seal repeatedly blowing out.
  do you mean it literally and physically blows out  ?

 
Quote
what is the actual timing
     I think I started to work it out but gave up on the  basis of 'suck and see'
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 16.03. 2016 09:08
How is the cork.
If the gasket is too thin it will not make a seal so the breather becomes effectivly useless.
Title: Re: Timed breather, what is the actual timing?
Post by: TT John on 16.03. 2016 19:10
I'm asking this on behalf of a friend who has had endless problems with crankcase pressure including the primary side crankcase oil seal repeatedly blowing out.

He has measured the timing (at the crank) of the the timed breather and told me that he got these results below, the question is, are these values "normal"?

Open  90 degrees before bdc
Close 45 degrees after bdc

If anyone has the dimensions of an unmodified breather (hole) I guess that that would also help.

I don't think there is any set timing, as long as the marks line up on the crank, idler sprocket & magneto, as these only line up after about eighty revolutions. I know I had the same problem but found that the return pipe was blocked with, most probably old silicon gasket material, I use an air line to blow all the old crap out.
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 16.03. 2016 21:11
Thanks for the replies, I think what Scott is trying to do is establish whether he has a non standard breather eg hole in wrong place or wrong length, he has investigated all other known reasons for excess crankcase pressure.

Scott glued the crankcase oil seal in place and it still blew out!

Its had a rebore and has gapless rings but still burns far too much oil.

Title: Re: Timed breather, what is the actual timing?
Post by: chaterlea25 on 16.03. 2016 21:19
Hi,
Quote
Its had a rebore and has gapless rings but still burns far too much oil

Sort this out and all will be well
More than likely the bores have glazed, what oil has been used?
Or a loose or worn valve guide(s)

John
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 16.03. 2016 23:18
Sorry it was not rebored just honed. Scott has just had the top end off to check the bores rings and guides etc. He Fixed a small end issue; but still the oil burning issue remains. He is reluctant to rebore what is an  in tolerance barrel until he is certain the timed breather is not at fault.

SAE 50 oil is used. Penrite, I think.
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 16.03. 2016 23:42
Sorry it was not rebored just honed. Scott has just had the top end off to check the bores rings and guides etc. He Fixed a small end issue; but still the oil burning issue remains. He is reluctant to rebore what is an  in tolerance barrel until he is certain the timed breather is not at fault.

SAE 50 oil is used. Penrite, I think.

let me know if you want a spare breather, I've got a stack of them  *eek*

He does live in NZ in the North Island ..., whats wrong with 40 weight. 50 is into big singles territory with roller big ends. too heavy an oil IMHO for plain big ends in the summer.
 But drop me a pm if you want a breather or two.
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 17.03. 2016 00:24
Hi Tim, careful this might turn into oil thread  *smile*

I use cheapo castrol gtx 20/50 myself  *pull hair out* *fight*

I'll ask Scott to get in touch with you then; in the mean time could you plesse measure the breather slot next time you visIt your shed full of breathers (and rocket 3 you lucky s_d).

Scott is obviously checking the non obvious as he has checked all thd obvious. He had a bunn breathet fitted to the breather  exit at one stage and that did not work either, albeit he had the std breather as well.
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 17.03. 2016 00:59
If he gets in touch I can stick one in the post.
I recall cake street classics recommend modifying the hole to extend the breathing.
Will try and find a couple. Being in a rental temporarily, I struggle to find anything or progress the bikes. Need that new big man cave  *rant*
Busy sorting out the electric leg on the R3  *shh*

my track A10 runs Bunn breathers, they're great  *respect*
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 17.03. 2016 06:53
otting gapless rings requie  few mods and willput a bit more pressure on the breathing system.
First thing is to sit behind him while he throttles on and then downchanges,
Smoke when throttleing on = bad seal on the rings
smoke on the over run = oil being sucked down the inlet valve guide
And as it is summer, check that the breather outlet is clean and dose not have a mud plugger of some sort stuck in there.
Also check the oil tank breather for the same problem.
Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 17.03. 2016 10:07
 
Quote
I recall cake street classics recommend modifying the hole to extend the breathing. 

 Wouldn't one need to take care doing this- might be OK on the blow side, but on the 'suck' side,might sick too much *eek*

 I'm inclined to go with TrevorTrevs line of thinking, you (he) should be able to poke a bit of wire up the gallery each way and blow air through (out)



Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 18.03. 2016 06:09
I've a copy of the cake street article and their mod was intended to increase performance rather improve breathing I reckon, they suggest elongating the hole in the breather to commence it opening earlier before bdc. The article does not give standard dimensions of the breather unfortunately.

Scotts bike uses in the region of a pint per 150 miles, more when the seal has blown out (mine is nearer 300 miles per pint and does not smoke) and whilst his bike doesn't smoke much it does smoke pretty much all the time (not great to be following behind it!), it's performance is good and it's mechanically quieter than (dammit).

If the breather is standard then he might have to try new rings, maybe a rebore, but the possibility that the excess pressure is causing the oil consumption is worth thoroughly investigating first.

Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 18.03. 2016 07:55

 But is the passage clear, and the tank breather too?
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 18.03. 2016 09:20
Hi Dutch, I'll ask about the tank breather and if it's been checked, but I'm puzzled as to why the oil tank breather could cause the engine to burn oil? If it's blocked, could it cause oil to build up in the crankcase?

Wouldn't  this also show up as a highly pressurised oil tank?

 Or would the rockers get too much oil? or what?

Edit: the breather exit has been checked and it's not blocked


Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 18.03. 2016 09:47

Ok main breather's not blocked... *dunno*

Quote
If it's blocked, could it cause oil to build up in the crankcase?

  It's obviously there for a reason, so not being an expert just after dark on a friday eve *beer* I'd say it'd cause some kind of backpressure buildup  to add to the carnkcase pressure as the engine heats up *????*
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 19.03. 2016 12:04
Gappless rings cause a much greater induction pressure to be generated in the cylinder and will suck oil down the inlet valve .
You need to fit a seal to the inlet.
You also need to open the inlet a bit earlier.
I am a fan of gapless rings but they need a bit of fettleing to work properly.
Total Seal used to have a tech page which lists recommended things to do when fitting gapless rings to older engines.
They make a massive difference to the induction draught as well as increased cylinder compression.
I have them fitter to a couple of the hire cars and they produce a lot more down low but stick the boot in and I could empty the sump in no time flat.
This is exactly why I asked when was it blowing smoke.
Also you must specify the cast iron gappless otherwise you will e supplied the steel rings which are very difficult the bed in.
Because they ar gapless they produce excellent compression readings even if they have not bedded in properly.
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 19.03. 2016 21:04
Hi Trevor, I will ask Scott what specification rings he fitted, I know they were Total Seal brand, also that he has not fitted oil seals on the inlet (that would involve custom guides?) but then on the other hand his bike does not puff smoke particularly badly on the over run like you'd expect if oil was being sucked in through the guides.

If his problem is caused by blow by, which is as a result of fitting gap less rings, I think the easiest option would be to go back to conventional rings! What seems odd to me is that one does not hear of oil seals blowing out due to serious excessive case pressure problems on engines needing rebores, which implies the blow by on his bike is really bad, yet his bike is not smoking that badly.

On a recent long run to Dunedin (after a top end rebuild, new small ends, and light rehone) he thinks the crankshaft oil seal blew out after around 150 miles of 60mph cruising this limited him to 50/55 mph for the next few hundred miles or so, but after that the engine gradually improved until we were back up to 60 mph (oops officer) plus at the 1000 mile mark, so the theory is maybe the rings are very slowly bedding in. They have done a few thousand miles in total now.

So his current plan is to glue the seal back in and give the current set up another go, but he would still like to know if his breather timing is standard!

Going back to prior question, the oil tank breather has been checked and is not blocked.



Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 20.03. 2016 07:38
The gap less rings spec is: brand Total Seal, gap less 2nd ring set, eg steel conventional top ring, gap less 2nd ring.


Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 20.03. 2016 09:57
Check that they are cast iron and not steel.
Total seal make a lot of steel rings and if you oreder by ring size and not engine type you can end up with wrong ring type.
The can aso be fitted upside down.
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 20.03. 2016 18:48
Hi Trev, As above he's definitely got a steel top ring (so potentially a bedding in problem there I think you said).

The spec of the other 2 rings is not yet known, but is cast iron even an available option from Total Seal for the gap less ring and oil ring? If so then he has potential bedding in problems there as well  *problem*

I'll check Scott is aware they fit one way up etc, I'm pretty sure he does know.
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 20.03. 2016 21:58
Had a quick rummage, managed to find 4 breathers, gave them a quick clean with kero, and was slightly surprised that one (with a straight taper rather than a concave end) appears to have different timing *conf2*
Photo's attached.
I can't tell you what they came out of.
Didnt the longstroke motors have a completely different breather set up  *dunno*
If so then some motors do have different breather timing  *roll*
Title: Re: Timed breather, what is the actual timing?
Post by: jachenbach on 21.03. 2016 02:45
So, Rocket's got a bunch of extra breathers. Not sure how many I've got (certainly more than I need). In the history of A10s has one ever worn out? Why are we saving these things????? Okay, I'm a packrat. Just can't bear to throw away any old part that MAY be needed someday. *smile*
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 21.03. 2016 03:12
So, Rocket's got a bunch of extra breathers. Not sure how many I've got (certainly more than I need). In the history of A10s has one ever worn out? Why are we saving these things????? Okay, I'm a packrat. Just can't bear to throw away any old part that MAY be needed someday. *smile*

Sadly those four are just the ones i found easily, there are more ..., as well as inner timing covers and other things no one will ever need  *whistle*
I  did wonder about making a bonzai tree from all the spare dynamo gears I've got  ;)
And I have a plan to build a "decorative" engine built up with mismatched and damaged parts either as a coffee table (sort of like the top gears porsche v8 one) or as a bar feature (if I had a bar   *beer*  )

Sorry, getting off topic
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 21.03. 2016 07:31
If only I could mission controls permission for a coffee table like that....  *bash*

This link to a prior topic might explain the different breathers?

http://www.a7a10.net/forum/index.php?topic=9624.msg70144#msg70144

Scotts is a latish A10 swing arm, 1959 or 1960 from memory.
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 22.03. 2016 06:58
a late type breathers gone in the post... Don't know if it'll arrive before easter but fingers crossed
Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 22.03. 2016 08:16

 Hey KiwiGF, unless I missed something, I guess we've all been just assuming that Scott has a BSA? maybe even an A10...? *smile*.

   If so, what model is it even, and I hope RR's breather helps.
 Maybe 'Scott' (or is he one of those imaginary friends *smile*) should join up? *beer*
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 22.03. 2016 09:50
Hi Dutch...he's not so imaginary!

http://www.stuff.co.nz/motoring/bikes/77816816/fatherson-bond-over-vintage-bsa-motorcycles

Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 22.03. 2016 11:11

 Ok,k, so the nudge gave results; great story, hopefully Scott and Jay will join in some time *smile*
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 24.03. 2016 10:03
We are getting a long way off topic here so I can 1/2 justify this speil.
Firstly the whole breathing thing and creating a partial vaccuum in the crankcase dates back to the era of oil slingers and felt seals.
No one bothered about it so no one actually thought about why we are doing it, they just did, and they did it wrong.

Air has a mass therefore there is a resistance to being moved and this applies just the same to flow through carburettors & valves as it does to crankcase venting.
Those who follow racing blue smokers will remember the massive leap in power that was attained when variable induction porting was introduced.
Those of you who play around with cam timing will also know that if it is right at idle it will be way out at 7000 rpm and visa versa.
This is due to the latiency of the moving gasses.

The exact same applies to breathers.
If it is right at idle it will be wrong every else.
The breather on an A series twin is right at speeds just above idle
Why?
because at idle and particularly at idle in the sales room you don't want a big puddle of oil dropping from the bottom of the bike.
If you can dig up Rex Bunns blog on the developement of the breather you will see some tables & graphs of crankcase pressures against engine revolutions and another of flow vrs engine revolutions.
They clearly show the mass inertia effect and that over certain rev ranges the system actually reverses itself and the breathers actually suck.
This was when he stopped looking for better valve material and turned towards flow through sytems.
Up to 1/3 rpm the M20 is oil tight with just a slight puff from the breather at 2/3 rpm it blows a continious stread of oil from the breather and at WFO the breather is again clean but oil pours out of the crankcase into the primary.
Title: Re: Timed breather, what is the actual timing?
Post by: duTch on 25.03. 2016 01:11

 Hey KiwiGF, did you sort it?

 I just heading out the door and had a thought while pondering my own, that if the filter in the bottom of the sump maybe blocked or too fine a mesh, may inhibit oil drainage and a buildup in the main chest?
   Maybe a bit far fetched, but if there's still an issue might be worth a look if not already discounted?

       *dunno*
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 27.03. 2016 22:39
Hi,

I tried to reply last night but it didn't appear. Maybe because I didn't put a long enough time to stay logged in. I am the guy who's A10 this is all about. I have now done an intro.
Status now:-
- Took on board BSA_54A10's points about valve guides with gapless. I am proposing to take my head to our local reconditioners. They say they can do K-liners if they can fit the jig in there. I will try to do both exhaust and inlet. My valves were sloppy in their guides. I also believe my smoking is on the overrun, more. I apologize - my gapless set has no steel rings.
The breather I got from Rocket Racer, thanks - is the same in all respects (later-model version, with taper not step). However, the peg hole is a bit further round to the right of the first breather hole. This would make it open and close a bit later. These all have the same part number 67987. Mine opens at 90 degrees btdc - which is the only timing specification I have gleaned from the forum. So, I propose to stick with that.
Title: Re: Timed breather, what is the actual timing?
Post by: KiwiGF on 28.03. 2016 09:08
Hi Scott any chance you could do your "find the breather timing trick"  *yeah* using Tim's breather?

So the forum has a record of the difference?

To me it's very odd *eek* there is difference between two parts with the same number, and given they spin at half engine speed a few degrees difference in the peg location might make quite a difference  to the timing  *dunno* but whether that significantly affects the breathers operation *dunno*
Title: Re: Timed breather, what is the actual timing?
Post by: Rocket Racer on 28.03. 2016 21:25
They say they can do K-liners if they can fit the jig in there. I will try to do both exhaust and inlet. My valves were sloppy in their guides.

We're moving onto a new topic here but I'm sure I have been warned off using K liners on aircooled motors (in my alloy heads) by several people in the past (5 years back??) ... cannot recall the details and may be quite mistaken.

But while a bit of smoke isnt doing much harm, money spent on a poor repair is heart breaking.

Please do some further research before going down that path
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 28.03. 2016 22:31
Hi KiwiGF and Rocket Racer,

Yes, I can do my timing trick on the other breather and let you know.
As regards K-liners, our engineer was ok with them  but had 2 provisos:-
- the clearances can't be as tight as car engines, for that very reason - ours are air-cooled engines, get hotter and the valves seize
- you have to support the guides top and bottom when you put the liners in, otherwise they split
I checked with the reconditioners and they can do them in cast-iron guides (as mine are) in an iron head, as long as they can fit the jig. I will make sure they know those provisos above.

Regards
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 29.03. 2016 11:37
K liners seem to be fine in the inlets but a bit dubious in the exhausts,
By now they should have worked out good running clearences but there were quite a few failures early on.
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 19.06. 2016 23:29
I need to follow up on this thread after having the k-liners installed.

The suspected excess clearance beforehand was verified by inspection. The inlets were about 3.5 thou". There was some confusion about the exhausts. The reconditioner thought one valve had worn 3 thou" but when we measured it when it was left over after the head was back together with a new one -  it was standard. I didn't get exact before measurements for exhausts therefore, but I believe they were sloppy. There was a lot of black deposit up both. He thinks that was evidence of pressure escaping up there - a suspected factor in crankcase pressure.

Anyway, we agreed on clearances with k-liners of: 1.5 thou" inlet; 2.5 thou" exhaust. He was pleased with his success after we had to order new inlet guides because one cracked. One other thing I did to mitigate crankcase pressure is to extend the holes in the timed breather valve. These were Dremelled out to the right (with hole on top) - according to the guidance in Roger Sharman's article. This makes them 12mm in length. They would open a bit earlier therefore and not allow as much pressure buildup on the downstroke. I know I can't isolate this from the k-liner effect, but I hope one of these measures will stop the drive-side seal blowing out. (The cork breather is good and compressed).

So the bike now runs very nicely. It is the best performance I have experienced with it. However, it still smokes a bit...I have measured the oil consumption and it is back to 1 pint in 200 miles. This is the best I have ever had but it's not good. This pint-in-200 is a standard that "one shouldn't worry if it was no worse than", apparently. I followed Jay on our ride back from Makara yesterday. He swapped onto the A10. The puffs were intermittent and alternate between left and right. They seemed to be when he revved after slowing down, what you call the "overrun" - which still suggests oil down the valve guides to me?

Anyway I will just run with this and see if the drive-side seal stays in place. The next step if it doesn't is a rebore. Remember I have the Total Seal gapless ring set. I have my old 8.5 to one comp pistons (BSA?). The clearance wasn't too big there apparently, but my engineer thinks there's a "scratch in one bore" where it rusted during years of sitting. This wasn't removed totally by the last honing apparently (about 2k miles ago). I think these rings have bedded in. They are supposed to "compensate for engine wear". I didn't get valve stem seals put in because this may have "starved the oil supply" a bit. They seem to be meant to compensate for wear too but we thought unnecessary with the k-liners. Total Seal do recommend seals.

I'm hoping that the remaining oil consumption isn't associated with factors that still might cause excess crankcase pressure (like piston blowby). If so, I'll just live with a bit of occasional smoke for now.

Thanks for listening and all the help so far...
Title: Re: Timed breather, what is the actual timing?
Post by: Peter in Aus on 20.06. 2016 10:42
Hi Scott & Jay, if you still have trouble with drive side seal coming out could try this (see pic) you have to make a small grove in the front bolt post just make sure you don't go right through to the hole, it is made out of about 1.5mm plate, I have done this on my 58 A10 and is working fine.
Peter
Title: Re: Timed breather, what is the actual timing?
Post by: muskrat on 20.06. 2016 11:32
Nice workaround Peter. Now do yourself a favor and drill and lockwire those two screws.
Cheers
Title: Re: Timed breather, what is the actual timing?
Post by: Peter in Aus on 20.06. 2016 12:38
Yes Musky I have done that, I should have mentioned that *good3*
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 30.01. 2017 22:40
Hi all,

I was encouraged to revive this thread by Anjimehra's issue (which is the opposite way round). I think I'd like to restrict the oil flow to the inlet rockers a tad. So, to recap:-
- I have a Total Seal Gapless ring set (just cast iron)
- I put K-liners in the valve guides - with tighter clearances than standard (2 1/2 thou" exhaust; 1 1/2 thou" inlet)
- this seems to have cured the crankcase pressure that kept blowing out the drive side oil seal (exhaust guide clearances were too high)
- the K-liners have caused no trouble after about 500 miles. The bike is going really well
I was discouraged by the reconditioner from putting seals in the inlet valve guides, against BSAA10_54's advice. I think my high oil consumption (pint in 190 miles) is from oil still being sucked (by the gapless rings), down the guides and burning . My own observation and others' following me seems to be the smoke puffs are on the "overrun". So, my question is - as at least an interim measure, do think there's any problem narrowing the rocker banjo inlet bolt hole down to 1mm (from the current, standard, 3/64" - which is same as exhaust one)?

Regards to all
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 on 31.01. 2017 10:44
None what so ever.
When I first started riding we would pinch off the return line to get more oil up the top where all us 15 year old "experts" knew it was needed.
By the time I was 18 the pinched off return tubes had been replaced & we were pinching off the rocker feed and drilling out the oil return holes.
The gapless rings put a lot more load on the breather and in the long run you would be better off going full flow through breathing.
The problem is air has mass so there fore there is a latiency in its movements.
The std BSA breather is only timed right to around 3000 rpm and from there on it gets further out of sync with the gas pressure pulses in the sump.
At certain speeds, it starts to work backwards.
Rex found this out when researching engine breathing and that is why he went to a through flow system rather than trying to create & maintain  low pressure in the crankcases.
This idea dates back to the earliest days of motorcycling when engines had no oil seals so you were sucking in through all of the scrolls and blowing out through the breather.
When oil seals were fitted every where, the same breathing systems were kept on and they have been failing ever since.

What was most important to BSA was the engines appeared oil tight in the dealers showrooms so all of the breather systems used is biased towards the lower engine revs.
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 31.01. 2017 20:34
Thanks very much again, for your help on this..
Title: Re: Timed breather, what is the actual timing?
Post by: Scott and Jay on 11.03. 2017 20:46
The story continues.. I found the same symptom - of oil over the back wheel, after some hard riding on the way up to the rally. The upshot is that the drive side crankcase seal hadn't been forced out this time. The crankcase pressure was all handled by the breather valve as timed. This is where the oil must have come from - out the exit pipe. So, I just have excess piston blowby - despite the gapless rings. The oil gets black pretty quickly. I was going through over a litre in 200 miles. I can't get any of those nice +80 Wiseco Pistons and rings from Cake Street. Roger has gone out of these now. I am finalising a set of pistons and rings from AdrianW (member and IDC Piston proprietor) - together with the liners to sleeve back to standard...
Title: Re: Timed breather, what is the actual timing?
Post by: Superflash on 23.02. 2020 05:43
Gents. Resurrecting a fairly old thread here, however I've been reading through a lot of the past posts about this subject trying to understand how it all works from a practical side of things. I understand the theory of having a breather etc, I'm just struggling with how it all actually works. Example....the breather itself sits on a peg located on the cam pinion. A cork spacer is used to get the cam end float to where it needs to be. the 2 holes in the breather will line up with the 2 holes in the inner timing case as it spins, thus allowing the expulsion of pressurised air.....right....got all that. 2 things have left me baffled though. is it only the inner timing case hole that the breather slides into, all that stops it falling off the cam pinion pin? And secondly, the inner timing case has 2 holes...one leads upwards and appears to vent into a hole in the main case. The other leads down, and presumably out of the case? I ask this last question because the tube leading downwards has been plugged. Should it be, and do I need to drill it out to create a clear pathway for escaping gases? Cheers
Title: Re: Timed breather, what is the actual timing?
Post by: muskrat 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
Title: Re: Timed breather, what is the actual timing?
Post by: Swarfcut 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.
Title: Re: Timed breather, what is the actual timing?
Post by: Superflash 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
Title: Re: Timed breather, what is the actual timing?
Post by: chaterlea25 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
Title: Re: Timed breather, what is the actual timing?
Post by: Swarfcut 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

 
Title: Re: Timed breather, what is the actual timing?
Post by: BSA_54A10 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.
Title: Re: Timed breather, what is the actual timing?
Post by: chaterlea25 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

Title: Re: Timed breather, what is the actual timing?
Post by: Slymo 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.
Title: Re: Timed breather, what is the actual timing?
Post by: muskrat 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